@Overrideprotected void onDraw(Canvas canvas) {if (running) {// get canvas current statefinal int state = canvas.save();// add circle to path to crate ripple animation// attention: you must reset the path first,// otherwise the animation will run wrong way.ripplePath.reset();ripplePath.addCircle(centerX, centerY, radius, Path.Direction.CW);canvas.clipPath(ripplePath);// the {@link View#onDraw} method must be called before// {@link Canvas#restoreToCount}, or the change will not appear.super.onDraw(canvas);canvas.restoreToCount(state);return;}// in a normal condition, you should call the// super.onDraw the draw the normal situation.super.onDraw(canvas);}Canvas#save()和Canvas#restoreToCount()

radiusAnimator = ObjectAnimator.ofFloat(this, "animValue", 0, 1);/*** This method will be called by {@link this#radiusAnimator}* reflection calls.** @param value animation current value*/public void setAnimValue(float value) {this.radius = value * maxRadius;System.out.println("radius = " + this.radius);invalidate();}

import android.animation.Animator;import android.animation.ObjectAnimator;import android.annotation.TargetApi;import android.content.Context;import android.graphics.Canvas;import android.graphics.Path;import android.util.AttributeSet;import android.view.View;import android.view.animation.AccelerateDecelerateInterpolator;import android.widget.ImageView;/*** Created by lion on 2016/11/11.* <p>* RippleImageView use the {@link Path#addCircle} function* to draw the view when {@link RippleImageView#onDraw} called.* <p>* When you call {@link View#invalidate()} function,then the* {@link View#onDraw(Canvas)} will be called. In that way you* can use {@link Path#addCircle} to draw every frame, you will* see the ripple animation.*/public class RippleImageView extends ImageView {// view center xprivate int centerX = 0;// view center yprivate int centerY = 0;// ripple animation current radiusprivate float radius = 0;// the max radius that ripple animation needprivate float maxRadius = 0;// record the ripple animation is runningprivate boolean running = false;private ObjectAnimator radiusAnimator;private Path ripplePath;public RippleImageView(Context context) {super(context);init();}public RippleImageView(Context context, AttributeSet attrs) {super(context, attrs);init();}public RippleImageView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);init();}@TargetApi(21)public RippleImageView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {super(context, attrs, defStyleAttr, defStyleRes);init();}private void init() {ripplePath = new Path();// initial the animator, when animValue change,// radiusAnimator will call {@link this#setAnimValue} method.radiusAnimator = ObjectAnimator.ofFloat(this, "animValue", 0, 1);radiusAnimator.setDuration(1000);radiusAnimator.setInterpolator(new AccelerateDecelerateInterpolator());radiusAnimator.addListener(new Animator.AnimatorListener() {@Overridepublic void onAnimationStart(Animator animator) {running = true;}@Overridepublic void onAnimationEnd(Animator animator) {running = false;}@Overridepublic void onAnimationCancel(Animator animator) {}@Overridepublic void onAnimationRepeat(Animator animator) {}});}@Overrideprotected void onLayout(boolean changed, int left, int top, int right, int bottom) {super.onLayout(changed, left, top, right, bottom);centerX = (right - left) / 2;centerY = (bottom - top) / 2;maxRadius = maxRadius(left, top, right, bottom);}/*** Calculate the max ripple animation radius.** @param left view left* @param top view top* @param right view right* @param bottom view bottom* @return*/private float maxRadius(int left, int top, int right, int bottom) {return (float) Math.sqrt(Math.pow(right - left, 2) + Math.pow(bottom - top, 2) / 2);}/*** This method will be called by {@link this#radiusAnimator}* reflection calls.** @param value animation current value*/public void setAnimValue(float value) {this.radius = value * maxRadius;System.out.println("radius = " + this.radius);invalidate();}@Overrideprotected void onDraw(Canvas canvas) {if (running) {// get canvas current statefinal int state = canvas.save();// add circle to path to crate ripple animation// attention: you must reset the path first,// otherwise the animation will run wrong way.ripplePath.reset();ripplePath.addCircle(centerX, centerY, radius, Path.Direction.CW);canvas.clipPath(ripplePath);// the {@link View#onDraw} method must be called before// {@link Canvas#restoreToCount}, or the change will not appear.super.onDraw(canvas);canvas.restoreToCount(state);return;}// in a normal condition, you should call the// super.onDraw the draw the normal situation.super.onDraw(canvas);}/*** call the {@link Animator#start()} function to start the animation.*/public void startAnimation() {if (radiusAnimator.isRunning()) {radiusAnimator.cancel();}radiusAnimator.start();}}