How do i check to see if a delegate is valid on the iPhone

Question

Hiya,

I'm doing something like this:

@protocol CallbackDelegate
-(void) performCallback;
@end

@interface MyObject : NSObject {
   id<CallbackDelegate> delegate;
}

-(void)AsyncFuncCall;

@end

@property (nonatomic, assign) id<CallbackDelegate> *delegate;

The code that owns MyObject sets up a delegate to recieve the callback function:

MyObject *myobject = [[MyOject alloc] init];
myobject.delegate = x;

Then in MyObject, as a result of an asynchronous function call I'll signal back to the delegate:

-(void)AsyncFuncCall {
   [delegate performCallback];
}

All seems to work well most of the time, except for the occasions where my delegate has been freed up as a result of valid memory cleanup. In this case, I simply want to not perform the callback

Does anyone know the best way to check to see if a delegate is valid?

I've tried all sorts of things such as:

if (delegate != nil) {
   ...
}

with no luck.

Thanks in advance!

Nick.

Answer 1

Your delegate should nil out myObject's delegate property in its dealloc to avoid this:

- (void) dealloc {
  if (myObject.delegate == self) myObject.delegate = nil;
  [super dealloc];
}

Alternatively, but not recommended, you could retain the delegate. However, this can lead to a retain cycle.