Checking if an object has been released before sending a message to it

I've only recently noticed a crash in one of my apps when an object tried to message its delegate and the delegate had already been released.

At the moment, just before calling any delegate methods, I run this check:

if (delegate && [delegate respondsToSelector:...]){
   [delegate ...];
}

But obviously this doesn't account for if the delegate isn't nil, but has been deallocated.

Besides setting the object's delegate to nil in the delegate's dealloc method, is there a way to check if the delegate has already been released just incase I no longer have a开发者_运维问答 reference to the object.

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No. There is no way to tell whether a variable points to a valid object. You need to structure your program so that this object's delegate isn't going away without letting it know first.

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I assume you're not using GC. In that case, standard convention is that the code that sets the delegate is responsible for setting the delegate-user's reference to nil before allowing the delegate to be deallocated. If you're using GC, you can use a __weak reference for the delegate, allowing the garbage collector to set the reference to nil when the instance is garbage collected.

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how about using a counter that you increment everytime you alloc and decrement everytime you dealloc. That way you could detect double allocs and could decide not to use a delegate if the counter isnt nil but the address isnt nil also

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for debug proposes you can override release method on your class to see when it is called.

-(oneway void)release
{
    NSLog(@"release called");
    [super release];
}