Announcements - and whether its bad to check if a subscription would be handled?
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent). Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated), And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense). In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words - e.g. SpellingTest â has many â> SpellingWord(s). Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials. This is where the announcements kick in (and lead to my ultimate question). When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method. Iâve been taking with Erik, on different ways to elegantly handle this. a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something. I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out). So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?). Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing: hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement" ^(registry subscriptionsHandling: anAnnouncement ) notEmpty And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this: viewCreated super viewCreated. self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ]; when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ? Tim
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement" ^(registry subscriptionsHandling: anAnnouncement ) notEmpty Tim On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
Exceptions are real, so your use case might justify it. In my experience I never had to test whether an announcer has some subscription, and before using announcements whether an object has some "listener" to some event. I always saw announcements as a fire and forget kind of architecture. Not sure if I'm answering your question (probably not), but let's start this conversation :-) Esteban A. Maringolo On Tue, Apr 27, 2021 at 11:04 AM Tim Mackinnon <tim@testit.works> wrote:
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
Tim
On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
The whole idea is to decouple producers and consumers, like in messaging systems. You should not care if there are other listening, just like the listeners should not care if there is someone posting data. Asking for subscribers is introducing a coupling. The announcement mechanism will/should deal with this in an efficient way.
On 27 Apr 2021, at 16:03, Tim Mackinnon <tim@testit.works> wrote:
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
Tim
On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
Hi guys - yes that fire and forget was always how I had viewed announcements, and potentially my scenario is misusing "announcements" which is why I was interested in views here. However - as announcements are typically a mechanism for farming out processing to others - how does one handle the scenario that you might only want one object to handle the announcement (and not others)? in my specific example, with MVP - a view, totally decoupled in a web browser, wants to pass on a button click to a presenter - however it not clear what the best mechanism to bubble up that handling should be? If the immediate presenter of the view can handle it - great - but if not, how would you continue to broadcast wider to see if someone higher up the parent component chain can handle it? If you go fire and forget (which is how I had viewed announcements prior to this specific case) - then you have the problem a different way - when someone processes an announcement it might already have been handled earlier and so the consumer either has to check first, or their work is simply ignored as the announcement payload could just filter a response out. In my head, I'm sort of thinking this is akin to CPU interrupt chaining - where an interrupt can cascade up a stack if not handled OR like object inheritance where an object can choose to override a message and stop it from cascading up the inheritance chain. Maybe announcements aren't intended for this at all - although it seems an elegant way to handle it - with just 1 method addition to Announcer (but it does slightly expose things - albeit in a structured way - and similar to the similar #hasSubscriber:). I'm sure it "depends" - but interested in other observations from the field, as I'm sure I'm not the first person to hit something like this. Tim On Tue, 27 Apr 2021, at 3:51 PM, Sven Van Caekenberghe wrote:
The whole idea is to decouple producers and consumers, like in messaging systems.
You should not care if there are other listening, just like the listeners should not care if there is someone posting data.
Asking for subscribers is introducing a coupling.
The announcement mechanism will/should deal with this in an efficient way.
On 27 Apr 2021, at 16:03, Tim Mackinnon <tim@testit.works> wrote:
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
Tim
On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
The bubbling up is very common in UI, I don't know how it is implemented though. I don't know if event handling is programmed using events or imperative calls to continue "bubbling" up, or... the event is handler by the container presenter and passed down to the target (e.g. a button). So the end user of the event registers the handling of an event directly at the component (presenter in MVP), regardless of who fires it. And it is the event object or the listener of the event that decides to stop its propagation. Regards, Esteban A. Maringolo On Tue, Apr 27, 2021 at 12:50 PM Tim Mackinnon <tim@testit.works> wrote:
Hi guys - yes that fire and forget was always how I had viewed announcements, and potentially my scenario is misusing "announcements" which is why I was interested in views here.
However - as announcements are typically a mechanism for farming out processing to others - how does one handle the scenario that you might only want one object to handle the announcement (and not others)?
in my specific example, with MVP - a view, totally decoupled in a web browser, wants to pass on a button click to a presenter - however it not clear what the best mechanism to bubble up that handling should be? If the immediate presenter of the view can handle it - great - but if not, how would you continue to broadcast wider to see if someone higher up the parent component chain can handle it?
If you go fire and forget (which is how I had viewed announcements prior to this specific case) - then you have the problem a different way - when someone processes an announcement it might already have been handled earlier and so the consumer either has to check first, or their work is simply ignored as the announcement payload could just filter a response out.
In my head, I'm sort of thinking this is akin to CPU interrupt chaining - where an interrupt can cascade up a stack if not handled OR like object inheritance where an object can choose to override a message and stop it from cascading up the inheritance chain.
Maybe announcements aren't intended for this at all - although it seems an elegant way to handle it - with just 1 method addition to Announcer (but it does slightly expose things - albeit in a structured way - and similar to the similar #hasSubscriber:).
I'm sure it "depends" - but interested in other observations from the field, as I'm sure I'm not the first person to hit something like this.
Tim
On Tue, 27 Apr 2021, at 3:51 PM, Sven Van Caekenberghe wrote:
The whole idea is to decouple producers and consumers, like in messaging systems.
You should not care if there are other listening, just like the listeners should not care if there is someone posting data.
Asking for subscribers is introducing a coupling.
The announcement mechanism will/should deal with this in an efficient way.
On 27 Apr 2021, at 16:03, Tim Mackinnon <tim@testit.works> wrote:
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
Tim
On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
The MVP scenario you describe with âbubbling upâ of event handling is how Dolphin implements command routing in MVP. Iâd suggest that what you need is an implementation of this, which is a separate mechanism to Announcements. Possibly your suggested solution is a clever way to implement a command mechanism by piggybacking Announcements..?
On 27 Apr 2021, at 16:49, Tim Mackinnon <tim@testit.works> wrote:
Hi guys - yes that fire and forget was always how I had viewed announcements, and potentially my scenario is misusing "announcements" which is why I was interested in views here.
However - as announcements are typically a mechanism for farming out processing to others - how does one handle the scenario that you might only want one object to handle the announcement (and not others)?
in my specific example, with MVP - a view, totally decoupled in a web browser, wants to pass on a button click to a presenter - however it not clear what the best mechanism to bubble up that handling should be? If the immediate presenter of the view can handle it - great - but if not, how would you continue to broadcast wider to see if someone higher up the parent component chain can handle it?
If you go fire and forget (which is how I had viewed announcements prior to this specific case) - then you have the problem a different way - when someone processes an announcement it might already have been handled earlier and so the consumer either has to check first, or their work is simply ignored as the announcement payload could just filter a response out.
In my head, I'm sort of thinking this is akin to CPU interrupt chaining - where an interrupt can cascade up a stack if not handled OR like object inheritance where an object can choose to override a message and stop it from cascading up the inheritance chain.
Maybe announcements aren't intended for this at all - although it seems an elegant way to handle it - with just 1 method addition to Announcer (but it does slightly expose things - albeit in a structured way - and similar to the similar #hasSubscriber:).
I'm sure it "depends" - but interested in other observations from the field, as I'm sure I'm not the first person to hit something like this.
Tim
On Tue, 27 Apr 2021, at 3:51 PM, Sven Van Caekenberghe wrote:
The whole idea is to decouple producers and consumers, like in messaging systems.
You should not care if there are other listening, just like the listeners should not care if there is someone posting data.
Asking for subscribers is introducing a coupling.
The announcement mechanism will/should deal with this in an efficient way.
On 27 Apr 2021, at 16:03, Tim Mackinnon <tim@testit.works> wrote:
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
Tim
On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
I have seen something called upcasting and downcasting (as contrasted with broadcasting). Mostly, I have seen it in UI layers. e.g. a leaf node receives a change notification, decides it isn't interested in handling the notification, and so passes it up to its parent, etc. Downcasting is similar but in the opposite direction. e.g. a window receives an event and asks its children to handle it, and they do the same. In this case especially, the one that handles the event needs to mark it as handled so that no one else is asked to handle it. On April 27, 2021 5:49:56 AM HST, Tim Mackinnon <tim@testit.works> wrote:
Hi guys - yes that fire and forget was always how I had viewed announcements, and potentially my scenario is misusing "announcements" which is why I was interested in views here.
However - as announcements are typically a mechanism for farming out processing to others - how does one handle the scenario that you might only want one object to handle the announcement (and not others)?
in my specific example, with MVP - a view, totally decoupled in a web browser, wants to pass on a button click to a presenter - however it not clear what the best mechanism to bubble up that handling should be? If the immediate presenter of the view can handle it - great - but if not, how would you continue to broadcast wider to see if someone higher up the parent component chain can handle it?
If you go fire and forget (which is how I had viewed announcements prior to this specific case) - then you have the problem a different way - when someone processes an announcement it might already have been handled earlier and so the consumer either has to check first, or their work is simply ignored as the announcement payload could just filter a response out.
In my head, I'm sort of thinking this is akin to CPU interrupt chaining - where an interrupt can cascade up a stack if not handled OR like object inheritance where an object can choose to override a message and stop it from cascading up the inheritance chain.
Maybe announcements aren't intended for this at all - although it seems an elegant way to handle it - with just 1 method addition to Announcer (but it does slightly expose things - albeit in a structured way - and similar to the similar #hasSubscriber:).
I'm sure it "depends" - but interested in other observations from the field, as I'm sure I'm not the first person to hit something like this.
Tim
On Tue, 27 Apr 2021, at 3:51 PM, Sven Van Caekenberghe wrote:
The whole idea is to decouple producers and consumers, like in messaging systems.
You should not care if there are other listening, just like the listeners should not care if there is someone posting data.
Asking for subscribers is introducing a coupling.
The announcement mechanism will/should deal with this in an efficient way.
On 27 Apr 2021, at 16:03, Tim Mackinnon <tim@testit.works> wrote:
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
Tim
On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere
either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its
associated
view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although
normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs
presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way
too
(and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
I appreciate the further thoughts of others - I should go back and look at Dolphin code (I think there are ways to run it on Mac now?). The upcasting Richard refers to is what I'm trying to do - which is how I got interested in understanding if you could tell if someone was subscribed to an event, as if not - then you could pass it up to the parent to - re-announce it via the announcer of that parent (in CP - the announcers are by presenter, so hence the handoff). In theory it's quite neat - but I did see some deprecations in Announcer trying to stop too much knowledge leaking out. However, knowing if an event has any listeners doesn't on the surface seem too controversial - but I can see that everyone approaches this idea with understandable caution. Possibly this is masking some other approach to this - or - I can happily have an extension method on Announcer - or - I can propose this method in a PR for symetry with some of the other #hasXXXX methods. Tim On Tue, 27 Apr 2021, at 5:31 PM, Richard Sargent wrote:
I have seen something called upcasting and downcasting (as contrasted with broadcasting). Mostly, I have seen it in UI layers.
e.g. a leaf node receives a change notification, decides it isn't interested in handling the notification, and so passes it up to its parent, etc.
Downcasting is similar but in the opposite direction. e.g. a window receives an event and asks its children to handle it, and they do the same. In this case especially, the one that handles the event needs to mark it as handled so that no one else is asked to handle it.
On April 27, 2021 5:49:56 AM HST, Tim Mackinnon <tim@testit.works> wrote:
Hi guys - yes that fire and forget was always how I had viewed announcements, and potentially my scenario is misusing "announcements" which is why I was interested in views here.
However - as announcements are typically a mechanism for farming out processing to others - how does one handle the scenario that you might only want one object to handle the announcement (and not others)?
in my specific example, with MVP - a view, totally decoupled in a web browser, wants to pass on a button click to a presenter - however it not clear what the best mechanism to bubble up that handling should be? If the immediate presenter of the view can handle it - great - but if not, how would you continue to broadcast wider to see if someone higher up the parent component chain can handle it?
If you go fire and forget (which is how I had viewed announcements prior to this specific case) - then you have the problem a different way - when someone processes an announcement it might already have been handled earlier and so the consumer either has to check first, or their work is simply ignored as the announcement payload could just filter a response out.
In my head, I'm sort of thinking this is akin to CPU interrupt chaining - where an interrupt can cascade up a stack if not handled OR like object inheritance where an object can choose to override a message and stop it from cascading up the inheritance chain.
Maybe announcements aren't intended for this at all - although it seems an elegant way to handle it - with just 1 method addition to Announcer (but it does slightly expose things - albeit in a structured way - and similar to the similar #hasSubscriber:).
I'm sure it "depends" - but interested in other observations from the field, as I'm sure I'm not the first person to hit something like this.
Tim
On Tue, 27 Apr 2021, at 3:51 PM, Sven Van Caekenberghe wrote:
The whole idea is to decouple producers and consumers, like in messaging systems.
You should not care if there are other listening, just like the listeners should not care if there is someone posting data.
Asking for subscribers is introducing a coupling.
The announcement mechanism will/should deal with this in an efficient way.
On 27 Apr 2021, at 16:03, Tim Mackinnon <tim@testit.works> wrote:
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
Tim
On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
Upcasting is a behavioural feature. You would not play with the announcements. The class would receive it and its handler would delegate to a parent if necessary. On Tue, Apr 27, 2021 at 10:14 AM Tim Mackinnon <tim@testit.works> wrote:
I appreciate the further thoughts of others - I should go back and look at Dolphin code (I think there are ways to run it on Mac now?).
The upcasting Richard refers to is what I'm trying to do - which is how I got interested in understanding if you could tell if someone was subscribed to an event, as if not - then you could pass it up to the parent to - re-announce it via the announcer of that parent (in CP - the announcers are by presenter, so hence the handoff).
In theory it's quite neat - but I did see some deprecations in Announcer trying to stop too much knowledge leaking out. However, knowing if an event has any listeners doesn't on the surface seem too controversial - but I can see that everyone approaches this idea with understandable caution. Possibly this is masking some other approach to this - or - I can happily have an extension method on Announcer - or - I can propose this method in a PR for symetry with some of the other #hasXXXX methods.
Tim
On Tue, 27 Apr 2021, at 5:31 PM, Richard Sargent wrote:
I have seen something called upcasting and downcasting (as contrasted with broadcasting). Mostly, I have seen it in UI layers.
e.g. a leaf node receives a change notification, decides it isn't interested in handling the notification, and so passes it up to its parent, etc.
Downcasting is similar but in the opposite direction. e.g. a window receives an event and asks its children to handle it, and they do the same. In this case especially, the one that handles the event needs to mark it as handled so that no one else is asked to handle it.
On April 27, 2021 5:49:56 AM HST, Tim Mackinnon <tim@testit.works> wrote:
Hi guys - yes that fire and forget was always how I had viewed announcements, and potentially my scenario is misusing "announcements" which is why I was interested in views here.
However - as announcements are typically a mechanism for farming out processing to others - how does one handle the scenario that you might only want one object to handle the announcement (and not others)?
in my specific example, with MVP - a view, totally decoupled in a web browser, wants to pass on a button click to a presenter - however it not clear what the best mechanism to bubble up that handling should be? If the immediate presenter of the view can handle it - great - but if not, how would you continue to broadcast wider to see if someone higher up the parent component chain can handle it?
If you go fire and forget (which is how I had viewed announcements prior to this specific case) - then you have the problem a different way - when someone processes an announcement it might already have been handled earlier and so the consumer either has to check first, or their work is simply ignored as the announcement payload could just filter a response out.
In my head, I'm sort of thinking this is akin to CPU interrupt chaining - where an interrupt can cascade up a stack if not handled OR like object inheritance where an object can choose to override a message and stop it from cascading up the inheritance chain.
Maybe announcements aren't intended for this at all - although it seems an elegant way to handle it - with just 1 method addition to Announcer (but it does slightly expose things - albeit in a structured way - and similar to the similar #hasSubscriber:).
I'm sure it "depends" - but interested in other observations from the field, as I'm sure I'm not the first person to hit something like this.
Tim
On Tue, 27 Apr 2021, at 3:51 PM, Sven Van Caekenberghe wrote:
The whole idea is to decouple producers and consumers, like in messaging systems.
You should not care if there are other listening, just like the listeners should not care if there is someone posting data.
Asking for subscribers is introducing a coupling.
The announcement mechanism will/should deal with this in an efficient way.
On 27 Apr 2021, at 16:03, Tim Mackinnon <tim@testit.works> wrote:
From my rather long ramble below - I am still curious if its distasteful to have a method on Announcer
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subscribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
Tim
On Thu, 22 Apr 2021, at 11:34 PM, Tim Mackinnon wrote:
Hi everyone - Iâve always thought the article on announcements many years ago was very cool - and we donât seem to use them as much as we could (but equally they arenât a panacea to be overused everywhere either - and they do get used in Pharo to some extent).
Anyway, Iâve been playing around with CodeParadise (CP is a very cool project, and Erik is very supportive and thinking about how to write web apps a different way⦠Iâm fascinated),
And - CP uses announcements as mechanism to send events from the View Client (in a web browser) to a Presenter on the server (which makes total sense).
In taking things for a spin, I hit an interesting problem on how in a web component world, you should display a spelling test of words -
e.g. SpellingTest â has many â> SpellingWord(s).
Initially I bunged it all in a single presenter with its associated view, and it was a bit messy, and Erik guided me down a route (that CP nicely supports) - that my SpellingTest view should have the name/date of the test as well as an add word input field, but the list of current Words (which I had bunged into a table) - were actually more elegant as sub-components - hence a WordView - which renders a single word in a DIV, and for the edit screen I was creating, a Delete button next to the word (so you could delete it). So a 1 to many relationship essentials.
This is where the announcements kick in (and lead to my ultimate question).
When you click the Delete button, if I use a sub component - my view will generate a DeleteWordAnnouncement - which gets fed to my SpellingWordPresenter - however words in this sense donât naturally know their parent (the SpellingTest) - and its the parent test that has a #deleteWord: method.
Iâve been taking with Erik, on different ways to elegantly handle this.
a) you could change the model so words know their parent (in my case, Iâm using a 3rd party model for Flashcards, and they just donât know this - and adapting them would be a nuisance b) my TestPresenter could listen to announcements on the WordPresenter - and I could get some communications between presenters (although normally the Presenters just get events from Views, and pure domain models - so it feels a bit abnormal to consider another Presenter as a sort of model - but I could live with this c) given the composable nature of views/presenters (and CP is base on a WebComponent model) - you could bubble up Announcements, so that if an event isnât handled by a viewâs immediate presenter, you could re-route it to the parent of the View (the component owner) and see if itâs presenter could do something.
I think (c) has a certain expectation to it - in fact when I converted my initial one-presenter attempt into components, I still had listener code in my TestPresenter that was expecting to get a deleteWord announcement and I was initially surprised that I wasnât getting it (as it was now just going to the Word component I had refactored out).
So I wonder if others here would expect things to work this way too (and are there other examples in the wild that lead you here - or scare you away from this?).
Back to my Announcement question - if C is a good idea - why doesnât the Announcer class let you check if if will handle a particular announcement? The API has #hasSubscriber: and #hasSubscriberClass: , but its missing:
hasSubscriptionsHandling: anAnnouncement "Answer true if I have any subcribers to anAnnouncement"
^(registry subscriptionsHandling: anAnnouncement ) notEmpty
And I am wondering if this is because it's a bad thing to expect to be able to check? In my case above, I would want to do this to know if CP should instead try announcing a message to a parent presenter because the current presenter wonât handle it. In my example above, my WordComponentView will broadcast that the delete button was clicked, but its actually a parent view which would reasonably want to listen to this kind of event and process the delete. And in a many words scenario (the Test has many words), its unrealistic for the parent to register to listen to each word component individually (in fact CP sort of hides this from you), however if you could listen to an event in your TestView, it seems to come out quite nicely - and looks a bit like this:
viewCreated super viewCreated.
self view when: CpNavigationAnnouncement do: [ :action | self model goto: action location ];
when: CpAddWordAnnouncement do: [ :action | self addWord: action data ]; when: CpDeleteWordAnnouncement do: [ :action | self deleteWord: action data ]. <â this is the one Iâm talking about
So Iâm curious on the overall thought process here, but in particular whether I should even submit a PR on Announcer for #hasSubscriptionsHandling: ?
Tim
participants (6)
-
Esteban Maringolo -
John Aspinall -
Richard Sargent -
Richard Sargent -
Sven Van Caekenberghe -
Tim Mackinnon