Android - getAlpha() from Animated View

问题

I have an animation like this:

Animation fadeOut = new AlphaAnimation(1, 0);
fadeOut.setInterpolator(new DecelerateInterpolator());
fadeOut.setDuration(350);
myView.startAnimation(fadeOut);

I am trying is to get its Alpha durring the Animation as such:

System.out.println(myView.getAlpha());

However, it always returns "1.0" throughout the animation. How can I obtain the actual alpha value of myView during the animation process?

回答1:

By using Transformation with your AlphaAnimation, you may be able to retrieve alpha value directly from your AlphaAnimation object instead of your View.

Purpose of using Transformation:

Defines the transformation to be applied at one point in time of an Animation.

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Steps:

1. Create a new Transformation.java class as shown in https://sourcegraph.com/android.googlesource.com/platform/frameworks/base/-/blob/core/java/android/view/animation/Transformation.java.

2. Initialize a Transformation object:

   private Transformation myTransformation;
   mTransformation = new Transformation();
   

3. Using your code:

   Animation fadeOut = new AlphaAnimation(1, 0);
   fadeOut.setInterpolator(new DecelerateInterpolator());
   fadeOut.setDuration(350);
   

4. Get the time at which the drawing of the view hierarchy started (in milliseconds):

   final long time = myView.getDrawingTime();
   

5. Get the transformation to apply at a specified point in time. Finally, obtain the actual alpha value during the animation:

   fadeOut.getTransformation(time, myTransformation);
   final float myAlphaValue = myTransformation.getAlpha();
   

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Resources: https://sourcegraph.com/android.googlesource.com/platform/frameworks/base/-/blob/core/java/android/widget/ProgressBar.java#L1699 https://developer.android.com/reference/android/view/animation/Animation.html https://developer.android.com/reference/android/view/animation/Transformation.html

来源：https://stackoverflow.com/questions/38435423/android-getalpha-from-animated-view