Question

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 receive 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.

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.