Question

In the code below, self is retained to assure that the image object lives when the block gets called. That’s what the docs say. However, I don’t seem to understand why. Simply retaining the image would have guarantee that it doesn’t get deallocated. So why retain self as well?

self.finishBlock = ^{
    self.image.hidden = YES;
}

Does this apply if you access the image directly?

self.finishBlock = ^{
    _image.hidden = YES;
}

Answer 1

A block needs to retain any captured objects in the block. Your first block example is really:

self.finishBlock = ^{
    [[self image] setHidden:YES];
}

The block must retain self so it can properly call the image method. As written the block can’t simply retain image because the image isn’t obtained until the block is executed and the image method is called. So the only option here is to retain self.

In the second block you really have:

self.finishBlock = ^{
    self->_image.hidden = YES;
}

so again, self must be retained so the proper value of the _image ivar is accessed when the block is actually executed.