AnimatableImageView with no content causes crash when deallocated

[flyinghyrax]

If an AnimatableImageView is initialized but otherwise never used, the application will crash when the AnimatableImageView is deallocated.

I believe the source of the problem is here: https://github.com/kaishin/Gifu/blob/master/Source/AnimatableImageView.swift#L94

If the view was created but no other methods were called, then the lazy displayLink property will not have been initialized, so the CADisplayLink is created when it is first accessed inside the deinit block.

The CSDisplayLink instance will attempt to retain the AnimatableImageView as its target, then immediately release it since the next thing that happens is the call to invalidate().

This can be avoided by creating a Bool property that is set to true when the displayLink property is first accessed (it can be set from inside the closure that constructs the property). Then check the property in deinit and only invalidate the display link if it was already otherwise initialized.

The issue can be reproduced with the sample project here (see the master branch of that repo for a Readme file with more detail).

I will open a pull request for this change, but it will conflict with #52.

[pbruz]

If fact there is more common problem with this deinit. IMO it has no chance to work properly. If you think about object life cycle, you will see that there is a releasing cycle and in fact it leads to crash. Even if you call startAnimatingGIF.
The problem is, as you mentioned, with deinit method.

Because CADisplayLink is always targeting `self`, after `deinit` is invoked, it causes calling `deinit` one more time. Never ending story...

[flyinghyrax]

@pbruz this may help with that: #55

[pbruz]

@mr-seiler Yeah, you're right. Sorry, I didn't see this. I had a problem with that before #55 was created. As a solution I used not so pretty key-value coding. But it would be nice to fix this :)