@Override
protected void onDraw(Canvas canvas) {
if (running) {
// get canvas current state
final 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 x
private int centerX = 0;
// view center y
private int centerY = 0;
// ripple animation current radius
private float radius = 0;
// the max radius that ripple animation need
private float maxRadius = 0;
// record the ripple animation is running
private 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() {
@Override
public void onAnimationStart(Animator animator) {
running = true;
}
@Override
public void onAnimationEnd(Animator animator) {
running = false;
}
@Override
public void onAnimationCancel(Animator animator) {
}
@Override
public void onAnimationRepeat(Animator animator) {
}
});
}
@Override
protected 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();
}
@Override
protected void onDraw(Canvas canvas) {
if (running) {
// get canvas current state
final 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();
}
}