How to dynamically adjust the duration/speed of a Tween Animation in Android

问题

Let's say I have an android app, and in that app I want to animate a graphic of a ball in an "L" shape. This would require me to define a Tween Animation where I create an animation xml file (written below) and apply it to a View which has the ball graphic in it.

<translate>
Ydelta = 20;
offset = 0;
duration = 100;
</translate>

<translate>
Xdelta = 20;
offset = 100;
duration = 100;
</translate>

Now lets say I want to control the speed of this animation dynamically so that over time, the L animation goes faster and faster and faster. How can I dynamically control the speed of this whole animation? I have tried myAnimation.setDuration($var) but this only seems to work on the first part of the animation. Any part of the animation that has an offset greater than 0 doesn't have its duration adjusted by the setDuration() method.

Does anyone know a way that I can scale a multi-setp animation uniformly?

Thanks

ps - I know there are ways around solving this such as creating a 2 part animation and scaling each part independently or generating an animation using code, but if there's a simpler solution then that would be preferred.

回答1:

I've solved this on my own. To scale the whole animation you need to programmatically create the animations, and when you set the animation duration using setDuration(); you pass it a variable, instead of hardcoding in xml.

Now each time I call my animation, I pass it the animation duration mAnimDuration and then create the new time scaled animation on-the-fly. You'll notice that the offset of the second part of the animation is set to the duration of the first part of the animation.

Here is an example from my code:

AnimationSet rootSet = new AnimationSet(true);

TranslateAnimation transX = new TranslateAnimation(Animation.RELATIVE_TO_SELF, 0, Animation.RELATIVE_TO_SELF, 2, 0,0,0,0);
transX.setStartOffset(0);  
transX.setDuration(mAnimDuration/2);  
rootSet.addAnimation(transX);

TranslateAnimation transX2 = new TranslateAnimation(Animation.RELATIVE_TO_SELF, 0, Animation.RELATIVE_TO_SELF, 2, 0,0,0,0);  
transX2.setStartOffset(mAnimDuration/2);  
transX2.setDuration(mAnimDuration/2);  
rootSet.addAnimation(transX2);

来源：https://stackoverflow.com/questions/3619663/how-to-dynamically-adjust-the-duration-speed-of-a-tween-animation-in-android