Bug 39218 - Unpause/resume on AnimationDrawable always started on the 0th frame
Summary: Unpause/resume on AnimationDrawable always started on the 0th frame
Status: RESOLVED ANSWERED
Alias: None
Product: Android
Classification: Xamarin
Component: Tools and Addins ()
Version: 4.4.x
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Jonathan Pryor
URL:
Depends on:
Blocks:
 
Reported: 2016-02-29 19:27 UTC by mli
Modified: 2016-03-03 17:48 UTC (History)
1 user (show)

Tags:
Is this bug a regression?: ---
Last known good build:


Attachments
Codes that reproduces the bug (42.37 KB, application/x-zip-compressed)
2016-02-29 21:54 UTC, mli
Details


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Status:
RESOLVED ANSWERED

Description mli 2016-02-29 19:27:38 UTC
Steps to reproduce:

1. Calling AnimationDrawable.SetVisible(false, false) to pause the animation.
2. Calling AnimationDrawable.SetVisible(true, false) to unpause/resume the animation from where it was paused.

Problem experienced:

Unpause/resume of the animation started on the 0th frame, instead of continuing from where it was paused.
Comment 1 Jonathan Pryor 2016-02-29 20:55:52 UTC
Please provide a reproducible test case.
Comment 2 mli 2016-02-29 21:54:53 UTC
Created attachment 15196 [details]
Codes that reproduces the bug

I have attached a simple project that demonstrates the issue. Any suggestions for the fix would be greatly appreciated.

Thank you very much!
Comment 3 mli 2016-02-29 22:45:47 UTC
Sample codes is also available on 

https://github.com/esharecodes/AnimationDrawableUnpause

Thanks!
Comment 4 mli 2016-03-01 14:29:29 UTC
Included test codes in the attachment and on GitHub.
Comment 5 Jonathan Pryor 2016-03-03 17:48:31 UTC
Thank you for Attachment #15196 [details]. I "ported" it to Java, and observed the same behavior, so this isn't a binding problem.

Investigating further...would you believe that the documentation is wrong? :-)

http://developer.android.com/reference/android/graphics/drawable/AnimationDrawable.html#setVisible(boolean,%20boolean)

> If restart is false, the animation will resume from the most recent frame.

That's not what the *implementation* does:

https://github.com/android/platform_frameworks_base/blob/9498e8a8d2deb7b0a2e964d5d3c5d3b8747610e9/graphics/java/android/graphics/drawable/AnimationDrawable.java#L119-L131

Specifically line 123-124:

    boolean startFromZero = restart || !mRunning ||
        mCurFrame >= mAnimationState.getChildCount();

When you call SetVisible(true, false), `restart` is false, but `changed` (see github) will be true, causing us to evaluate line 123. mRunning will be `false` (see unscheduleSelf(), called by setVisible(), so startFromZero is:

    boolean startFromZero = false || !false || ...

which means startFromZero will be *true*, which is why we observe that the animation restarts at frame 0.

I'm currently unable to ascertain *how* this is *supposed* to work.

Guess: perhaps SetVisible(true, true) is for one-shot animations:

https://books.google.com/books?id=39Jlo3nZ7HIC&pg=PT104&lpg=PT104&dq=AnimationDrawable.SetVisible&source=bl&ots=MLV1bWiH4p&sig=j1otKi-OupsBx0QmdeB7I-PiuOM&hl=en&sa=X&ved=0ahUKEwjF04X64qTLAhWGFT4KHXj_AXUQ6AEIRDAH#v=onepage&q=AnimationDrawable.SetVisible&f=false

while SetVisible(true, false) is meaningless when done after a SetVisible(false,*)? I'm not sure, but that certainly *seems* to be the case.