Add Gif loop end listener

[AnwarShahriar]

Description

This PR adds a listener to the GifDrawable to listen to gif loop end, when it's explicitly specified by the user.

Possibly solves #1872

Motivation and Context

I worked on a feature for showing and stopping a gif after certain loop count. The spec was,

• Show Gif in a RecyclerView
• Render it as a static picture (first frame of the Gif), but with an UI indicator that the picture is a gif
• When the user taps on the gif, hide the UI indicator and start playing it
• After 3 times of looping, stop the Gif and show the UI indicator again on top of the static first frame again.

To implement the above spec, (showing and hiding some UI stuff based on the Gif start/stop) I need to know when the Gif finishes looping 3 times. As glide doesn't expose decoder from GifDrawable and we cannot use anything other than GifDrawable in Request listener for gifs, I had to add a callback that can notify client when certain amount of looping finishes. This solution solves my issue and I wanted to share it with the community.

Please, let me know if it can be done in better way or any more work I need to do.

[sjudd]

Good idea and thank you for putting this together. However it's probably best to stick to the Android interfaces. Can you change this to use Animatable2Compat? https://developer.android.com/reference/android/support/graphics/drawable/Animatable2Compat

[AnwarShahriar]

@sjudd I'm a bit confused, and before putting more code I just want to make sure I'm understanding you correctly. Are you suggesting something like this?

@Override
public boolean onResourceReady(GifDrawable gifDrawable, Object model, Target<GifDrawable> target, DataSource dataSource, boolean isFirstResource) {
  gifDrawable.setLoopCount(3);
  gifDrawable.setGifLoopEndedListener(new Animatable2Compat.AnimationCallback() {
    @Override
    public void onAnimationEnd(Drawable drawable) {
      // Animation is done. update the UI or whatever you want
    }
  });
  return false;
}

If this is our intention, shouldn't we also provide the onAnimationStart implementation? The unused interface may create confusion. What do you think?

[sjudd]

@AnwarShahriar That's similar to what I'm suggesting. I'm suggesting making GifDrawable implement Animatable2Compat:

class GifDrawable implements Animatable, Animatable2Compat {
...

Your listener would just be a Animatable2Compat.AnimationCallback. You'd add and remove with the register/unregister methods in Animatable2Compat:

@Override
public boolean onResourceReady(GifDrawable gifDrawable, Object model, Target<GifDrawable> target, DataSource dataSource, boolean isFirstResource) {
  gifDrawable.setLoopCount(3);
  // Note that you'd need to unregister this in onLoadCleared to avoid a potential memory leak.
  gifDrawable.registerAnimationCallback(new Animatable2Compat.AnimationCallback() {
    @Override
    public void onAnimationEnd(Drawable drawable) {
      // Animation is done. update the UI or whatever you want
    }
  });
  return false;
}

Does that help clarify?

[AnwarShahriar]

@sjudd updated the PR. Let me know if I need to modify anything.

[stale]

This issue has been automatically marked as stale because it has not had activity in the last seven days. It will be closed if no further activity occurs within the next seven days. Thank you for your contributions.

[sjudd]

Thanks! Sorry for the delay.

[sjudd]

I'd either skip this check or make it a Precondition. I think with the @NonNull annotation you're fine just skipping the check.

If you do want a check, I'd prefer a Precondition because it would immediately show the developer where they went wrong, where the existing check will just silently fail.

[AnwarShahriar]

fixed

[sjudd]

ditto here for animationCallback, I think you can skip the null check with the annotation (or make it a Precondition if you want one).

[AnwarShahriar]

fixed

[AnwarShahriar]

@sjudd fixed as you suggested.

[AnwarShahriar]

@sjudd is there any update?

[stale]

This issue has been automatically marked as stale because it has not had activity in the last seven days. It will be closed if no further activity occurs within the next seven days. Thank you for your contributions.

[sjudd]

Two minor javadoc nits, otherwise looks good, thanks!

[sjudd]

Worth noting that this will only be called if the Gif stops because it reaches the loop count. It doesn't look like you're notifying if someone calls stop() directly.

[sjudd]

You can probably avoid javadoc for these methods that isn't specific to their behavior in this particular class. The javadoc for the interface will be shown by default.

[AnwarShahriar]

@sjudd docs are updated

[sjudd]

Thanks!

[pietroconta]

 gifDrawable.setGifLoopEndedListener(new Animatable2Compat.AnimationCallback() {
    @Override
    public void onAnimationEnd(Drawable drawable) {
      // Animation is done. update the UI or whatever you want
    }
  });

i dont know why i have this error: Cannot resolve method 'setGifLoopEndedListener' in 'GifDrawable