Re: Forwarding messages from an application delegate

FROM : Graham Cox
DATE : Fri May 02 16:44:29 2008

You also need to override -respondsToSelector: and return a logical OR 
of your delegate plus the old delegate's response, something like:

- (BOOL)    respondsToSelector:(SEL) aSelector
{
   BOOL responds = [super respondsToSelector:aSelector];
   
   if( !responds )
       responds = [[self oldDelegate] respondsToSelector:aSelector];
       
   return responds;
}

Also, forwardInvocation isn't called unless your object has already 
rejected the message, so its implementation should look like:

- (void)    forwardInvocation:(NSInvocation*) invocation
{
    SEL aSelector = [invocation selector];

    if ([[self oldDelegate] respondsToSelector:aSelector])
        [invocation invokeWithTarget:[self controller]];
    else
        [self doesNotRecognizeSelector:aSelector];
}


hth,


G.




On 3 May 2008, at 12:35 am, Matthew Gertner wrote:

> Hi,
>
> I am implementing an application delegate for a framework (Mozilla)
> that already registers its own delegate internally. Ideally I would
> like to be able to handle specific delegate messages in my class (in
> this case adding items to the dock tile menu) and forward all other
> invocations to the old delegate. So before I call [[NSApplication
> sharedApplication] setDelegate] for my delegate, I retrieve the
> existing delegate and save it in a member variable (mOldDelegate). I
> thought that I could get invocations to forward automatically like
> this:
>
> - (void)forwardInvocation:(NSInvocation *)anInvocation
> {
> if ([mOldDelegate respondsToSelector:[anInvocation selector]])
>  [anInvocation invokeWithTarget:mOldDelegate];
> else
>  [super forwardInvocation:anInvocation];
> }
>
> - (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector
> {
> if ([mOldDelegate respondsToSelector:aSelector])
>  return [mOldDelegate methodSignatureForSelector:aSelector];
> else
>  return [super methodSignatureForSelector: aSelector];
> }
>
> For some reason neither methodSignatureForSelector nor
> forwardInvocation is ever called. Perhaps this has something to do
> with the way messages are sent to the delegate by the application. As
> a result, my delegate never forwards to the old delegate. Any guidance
> would be appreciated.
>
> Matt
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