Reversing an Animation

问题:

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 recoding it and reversing the parameters?

回答1:

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());

回答2:

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.

回答3:

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);

回答4:

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;        
    }
}

回答5:

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

回答6:

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>

回答7:

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.

回答8:

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