Use proxy object to prevent strong reference cycle

[flyinghyrax]

This is a fix for the memory leak issue described in this comment on issue #12.

Although the deinit block called displayLink.invalidate(), because the CADisplayLink was retaining the AnimatableImageView instance the view was never deallocated, its deinit block never executed, and .invalidate() was never called.

We can fix the retention cycle between AnimatableImageView and CADisplayLink by using another object as the target for the CADisplayLink instance, as described here.

Here is the Instrument trace showing my test application running with this patch: gifu-leak-fixed.trace.zip. (Compare with the original trace from the comment linked above: gifu-leak-demo.trace.zip)

Screenshot of instrument results:

[stanmots]

Well done! And just to add my 2 cents: I think, the only reason for using prepareForReuse method was due to this memory leak issue. Maybe it's better to mark it as deprecated now. For this purpose Swift provides the attribute:

@available(*, deprecated, message="This method will be removed in the next version!")

[kaishin]

Thank you @mr-seiler for the outstanding work. I am going over the PR and the demo project. I confirmed the retain cycle and will merge this shortly.

[flyinghyrax]

Glad to help 👍