WidthAnimation.java

package net.prunusmume.sample;

import android.view.View;
import android.view.animation.Animation;
import android.view.animation.Transformation;


public class WidthAnimation extends Animation {

    private final View mTargetView;
    private final int mStartWidth;
    private final int mTargetWidth;

    public WidthAnimation(final View targetView, final int startWidth, final int targetWidth) {
        mTargetView = targetView;
        mStartWidth = startWidth;
        mTargetWidth = targetWidth;
    }

    @Override
    protected void applyTransformation(final float interpolatedTime, final Transformation t) {
        mTargetView.getLayoutParams().width = (int) (mStartWidth + (mTargetWidth - mStartWidth) * interpolatedTime);
        mTargetView.requestLayout();
    }

    @Override
    public boolean willChangeBounds() {
        return true;
    }
}