Question

I have a pretty simple setup for this unit test. I have a class that has a delegate property:

@interface MyClass : NSObject
...
@property (nonatomic, weak) id<MyDelegateProtocol> connectionDelegate;
...
@end

and I set the delegate in my test:

- (void)testMyMethod_WithDelegate {
  id delegate = mockDelegateHelper(); // uses OCMock to create a mock object
  [[delegate expect] someMethod];
  myClassIvar.connectionDelegate = delegate;
  [myClass someOtherMethod];
  STAssertNoThrow([delegate verify], @"should have called someMethod on delegate.");
}

But the delegate is not actually set on line 3 of my unit test, so #someMethod is never called. When I change it to

myClassIvar.connectionDelegate = delegate;
STAssertNotNil(myClassIvar.connectionDelegate, @"delegate should not be nil");

it fails there. I’m using ARC, so my hunch was that the weak property was being deallocated. Sure enough, changing it to strong makes the STAssertNotNil pass. But I don’t want to do that with a delegate, and I don’t understand why that makes a difference here. From what I’ve read, all local references in ARC are strong, and STAssertNotNil(delegate) passes. Why is my weak delegate property nil when the same object in a local variable is not?

Answer 1

This is a bug in the iOS runtime. The following discussion has more detail. In a nutshell, the iOS ARC runtime can’t seem to handle weak references to proxies. The OSX runtime can.

http://www.mulle-kybernetik.com/forum/viewtopic.php?f=4&t=252

As far as I understand from the discussion a bug report has been filed with Apple. If anyone has a sensible idea for a workaround…