Reversing an Animation

I have an ImageView that gets animated when it is added to a layout. When it is removed, I want to reverse the same animation.

Is there a way to reverse an animation in android without re开发者_如何转开发coding it and reversing the parameters?

No, sadly you cannot do it with the Animation object. But you can simulate it using an interpolator that will inverse the animation:

package com.example.android;

import android.view.animation.Interpolator;

public class ReverseInterpolator implements Interpolator {
    @Override
    public float getInterpolation(float paramFloat) {
        return Math.abs(paramFloat -1f);
    }
}

Then on your animation you can set your new interpolator:

myAnimation.setInterpolator(new ReverseInterpolator());

If you are using Object or ValueAnimator to animate the view, you can simply do

ValueAnimator myAnimator = new ValueAnimator();  
myAnimator.reverse()

Documentation can be found here.

Based on pcans idea, you can reverse any interpolator, not just linear.

class ReverseInterpolator implements Interpolator{
    private final Interpolator delegate;

    public ReverseInterpolator(Interpolator delegate){
        this.delegate = delegate;
    }

    public ReverseInterpolator(){
        this(new LinearInterpolator());
    }

    @Override
    public float getInterpolation(float input) {
        return 1 - delegate.getInterpolation(input);
    }
}

Usage

ReverseInterpolator reverseInterpolator = new ReverseInterpolator(new AccelerateInterpolator())
myAnimation.setInterpolator(reverseInterpolator);

I have a similar approach to pcans buts slightly different. It takes an Interpolator and will effectively pass out values that would be the same as using the passed in Interpolator normally and then in REVERSE mode. Saves you having to think about the buggy implementations of Animation.REVERSE across Android. See the code here

public class ReverseInterpolator implements Interpolator {

    private final Interpolator mInterpolator;

    public ReverseInterpolator(Interpolator interpolator){
        mInterpolator = interpolator;
    }

    @Override
    public float getInterpolation(float input) {
        return mInterpolator.getInterpolation(reverseInput(input));
    }

    /**
     * Map value so 0-0.5 = 0-1 and 0.5-1 = 1-0
     */
    private float reverseInput(float input){        
        if(input <= 0.5)
            return input*2;
        else
            return Math.abs(input-1)*2;        
    }
}

Simplest solution i came up with

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android" android:interpolator="@android:anim/linear_interpolator">
    <alpha
        android:duration="2000"
        android:fromAlpha="0.1"
        android:repeatCount="infinite"
        android:repeatMode="reverse"
        android:toAlpha="1.0">
    </alpha>
</set>

You can make the code remember the original position and the end position. And let your code dynamically get those values when triggering animation.

If you are using animation from xml then an easy way is to made an exact same reverse animation to original animation. Add Animation.AnimationListener to original animation and in onAnimationEnd method start the reverse animation.

this worked for me

 ObjectAnimator anim = ObjectAnimator.ofFloat(imageViewUpb, "rotation", rotationAngle, rotationAngle + 180);

            if (linearLayoutb.getVisibility()==GONE){

                linearLayoutb.setVisibility(VISIBLE);
                anim.setDuration(500);
                anim.start();
                rotationAngle += 180;
                rotationAngle = rotationAngle%360;
        imageViewUpb.animate().rotation(rotationAngle).setDuration(500).start();

            }else{

                linearLayoutb.setVisibility(GONE);
                anim.setDuration(500);
                anim.start();
                rotationAngle += 180;
                rotationAngle = rotationAngle%180;
imageViewUpDownb.animate().rotation(rotationAngle).setDuration(500).start();

            }

linearlayoutb is the view that expands when the imageviewUpb faces up

make int rotationAngle = 0; global parameter

You need to use RepeatCount and RepeatMode

kotlin

   var anim = TranslateAnimation(0, 100, 0, 100)
   anim.repeatCount = Animation.INFINITE // you cant 1,2,...
   anim.repeatMode = Animation.REVERSE // you can set REVERSE or RESTART
   anim.start()

Since other answers have already been answered in Java, I will answer in Kotlin

// code inside onViewCreated()
...
        var anim: TranslateAnimation = TranslateAnimation(0F,60F,0F, 0F)
        anim.duration = 3000
        anim.fillAfter = true
        anim.repeatCount = -1
        anim.repeatMode = Animation.REVERSE // back and forth
        binding.asteroid.startAnimation(anim)
...

This is the simplest approach in Kotlin.