What is the proper way to avoid Retain Cycle while using blocks

问题

What is the proper way to add objects in NSMutableArray which is strongly defined by property.

[tapBlockView setTapBlock:^(UIImage* image) {
   [self.myImageArray addObject:image]; // self retain cycle
}

If I will create weak reference something like

__weak NSMutableArray *array = self.myImageArray;
[tapBlockView setTapBlock:^(UIImage* image) {
    [array addObject:image]; // If I will do this then how will I update original Array ?
}

I have also tried

__weak id weakSelf = self;
[tapBlockView setTapBlock:^(UIImage* image) {
    [weakSelf storeImageInaNewMethod:image]; // Calling SToreImageInaNewMethod
}

and

-(void)storeImageInaNewMethod:(UIImage*)image {
   [self.myImageArray addObject:image]; // This again retaining cycle
}

What is the proper way to update original object defined by property ?

回答1:

Try a combination of the 2nd and 3rd.

__weak id weakSelf = self;
[tapBlockView setTapBlock:^(UIImage* image) {
    [weakSelf.myImageArray addObject:image];
}

回答2:

After maddy's answer - this is from 2012 WWDC lecture on GCD and asynchronous programming:

__weak MyClass *weakSelf = self;

[tapBlockView setTapBlock:^(UIImage* image) {
    __strong MyClass *strongSelf = weakSelf;
    if(strongSelf) {
        [strongSelf.myImageArray addObject:image];
    }
}];

回答3:

In your case you only need to reference an array which is referenced by self, so:

NSMutableArray *array = self.myImageArray;
[tapBlockView setTapBlock:^(UIImage* image)
                          {
                             [array addObject:image]; // No cycle
                          }];

Works fine provided that self.myImageArray does not return different array references at different times. There is no cycle: the current object references the array and the block, and in turn the block references the array.

If self.myImageArray does return different array references as different times then use a weak reference to self, your case 3.

回答4:

Your second and third ones appear correct. The second one works because you did not create a copy of the array, so that still points to the original one. The third one works because the reference to self is weak.

来源：https://stackoverflow.com/questions/13257356/what-is-the-proper-way-to-avoid-retain-cycle-while-using-blocks

标签

iphone

objective-c

automatic-ref-counting

block

weak