Objective C: GestureRecognizer in ViewController -

问题:

I have the following property defined in the header file of one of my ViewControllers (VC):

@property(nonatomic, retain) IBOutlet UIImageView *articleImageView1;

In the implementation of the VC, in the method viewDidLoad, I attach TapRecognizers to these properties:

UITapGestureRecognizer *captureImage1TapRecognizer = [[UITapGestureRecognizer alloc]
                                                      initWithTarget:self
[self.articleImageView1 addGestureRecognizer:captureImage1TapRecognizer];

The VC holds strongly the UIImageView.

1. Does this UIImageView also contain the VC strongly through the GestureRecognizer?
2. Is this then a classical example of a retain cycle?

3. If so, would this be correct solution?

   -(void)viewDidUnload {
        ...
       [self setArticleImageView1:nil];
        ...
       [super viewDidUnload];
   }
   

回答1:

From Concepts of Obj-C programming on target - action pattern:

Control objects do not (and should not) retain their targets

Thus UIGestureRecognizer does not retain VC and there is no retain cycle.

Additional remarks

As pointed out by skyddict, -viewDidUnload has been deprecated and you should use -dealloc to perform cleanup. However, you don't need to nil your properties - they are released when object is destroyed.

回答2:

First of all, all IBOutlet properties should be declared as weak and not retain. Secondly, viewDidUnload has been deprecated since iOS 6.0. You should use dealloc in order to do the final cleanup for any NSObject subclass (you override this method to dispose of resources other than the object’s instance variables).

If you have the image view declared as weak, there won't be any retain cycles.You don't have to retain the IBOutlet (since it's already retained by it's superview). If you make IBOutlets weak, you won't have to nil them out as you point out.

回答3:

You don't have a strong reference cycle here. This is a solution that should work just fine.

The view controller has a strong reference to the UIImageView. The UIImageView holds its gesture recognizers in an array (strong reference as well), but the gesture recognizer does not hold target/action or delegate strongly.

You may hold onto the UIImageView via a weak reference, but since iOS 6 views are not unloaded anymore, so it won't make any difference for memory management.