I found strange to force user to write

Before invoking a delegation method, make sure the delegate implements it by sending it a

respondsToSelector: message.

Cocoa Fundamentals Guide (TP40002974 6.0.0) 
- (void)someMethod {

if ( [delegate respondsToSelector:@selector(operationShouldProceed)] ){ 

        if ( [delegate operationShouldProceed] ) {
            // do something appropriate

} }

}

I'm reading also on bindings (could be like valueHolder) and targetAction.
I think that I will have to read that several times :)

https://developer.apple.com/legacy/library/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaFundamentals.pdf

Stef

Cocoa Fundamentals Guide (TP40002974 6.0.0)
On 16/7/14 10:48, stepharo wrote:
Hi

In the quest for a better UI framework :), I was re rereading about delegate in Cocoa.
A delegating object will delegate certain operations to a delegate object (check the attachment).
Now I was wondering why this is not a simple delegation they wrote:

The delegating object sends a message only if the delegate implements the method. It makes this discovery by invoking the NSObject method respondsToSelector: in the delegate first.

Cocoa Fundamentals Guide (TP40002974 6.0.0)