Android实现水波纹特效

<RelativeLayout
  android:id="@+id/rl"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:gravity="center"
  android:layout_marginBottom="160dp" 
  <!--中心imageView-- 
  <ImageView
    android:id="@+id/iv_wave"
    android:layout_width="150dp"
    android:layout_height="150dp"
    android:layout_centerHorizontal="true"
    android:background="@drawable/shape_circle" / 
  <!--中间的imageView-- 
  <ImageView
    android:id="@+id/iv_wave_1"
    android:layout_width="150dp"
    android:layout_height="150dp"
    android:layout_centerHorizontal="true"
    android:background="@drawable/shape_circle" / 
  <!--最外层imageView-- 
  <ImageView
    android:id="@+id/iv_wave_2"
    android:layout_width="150dp"
    android:layout_height="150dp"
    android:layout_centerHorizontal="true"
    android:background="@drawable/shape_circle" / 
</RelativeLayout 

private void setAnim1() {
  AnimationSet as = new AnimationSet(true);
  //缩放动画，以中心从原始放大到1.4倍
  ScaleAnimation scaleAnimation = new ScaleAnimation(1.0f, 1.4f, 1.0f, 1.4f,
      ScaleAnimation.RELATIVE_TO_SELF, 0.5f,
      ScaleAnimation.RELATIVE_TO_SELF, 0.5f);
  //渐变动画
  AlphaAnimation alphaAnimation = new AlphaAnimation(1.0f, 0.5f);
  scaleAnimation.setDuration(800);
  scaleAnimation.setRepeatCount(Animation.INFINITE);
  alphaAnimation.setRepeatCount(Animation.INFINITE);
  as.setDuration(800);
  as.addAnimation(scaleAnimation);
  as.addAnimation(alphaAnimation);
  iv1.startAnimation(as);
}
private void setAnim2() {
  AnimationSet as = new AnimationSet(true);
  //缩放动画，以中心从1.4倍放大到1.8倍
  ScaleAnimation scaleAnimation = new ScaleAnimation(1.4f, 1.8f, 1.4f, 1.8f,
      ScaleAnimation.RELATIVE_TO_SELF, 0.5f,
      ScaleAnimation.RELATIVE_TO_SELF, 0.5f);
  //渐变动画
  AlphaAnimation alphaAnimation = new AlphaAnimation(0.5f, 0.1f);
  scaleAnimation.setDuration(800);
  scaleAnimation.setRepeatCount(Animation.INFINITE);
  alphaAnimation.setRepeatCount(Animation.INFINITE);
  as.setDuration(800);
  as.addAnimation(scaleAnimation);
  as.addAnimation(alphaAnimation);
  iv2.startAnimation(as);
}

<declare-styleable name="SpreadView" 
  <!--中心圆颜色-- 
  <attr name="spread_center_color" format="color" / 
  <!--中心圆半径-- 
  <attr name="spread_radius" format="integer" / 
  <!--扩散圆颜色-- 
  <attr name="spread_spread_color" format="color" / 
  <!--扩散间距-- 
  <attr name="spread_distance" format="integer" / 
  <!--扩散最大半径-- 
  <attr name="spread_max_radius" format="integer" / 
  <!--扩散延迟间隔-- 
  <attr name="spread_delay_milliseconds" format="integer" / 
</declare-styleable 

public SpreadView(Context context) {
  this(context,null,0);
}
 
public SpreadView(Context context, @Nullable AttributeSet attrs) {
  this(context, attrs,0);
}
 
public SpreadView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.SpreadView, defStyleAttr, 0);
  radius = a.getInt(R.styleable.SpreadView_spread_radius, radius);
  maxRadius = a.getInt(R.styleable.SpreadView_spread_max_radius, maxRadius);
  int centerColor = a.getColor(R.styleable.SpreadView_spread_center_color, ContextCompat.getColor(context, R.color.colorAccent));
  int spreadColor = a.getColor(R.styleable.SpreadView_spread_spread_color, ContextCompat.getColor(context, R.color.colorAccent));
  distance = a.getInt(R.styleable.SpreadView_spread_distance, distance);
  a.recycle();
  centerPaint = new Paint();
  centerPaint.setColor(centerColor);
  centerPaint.setAntiAlias(true);
  //最开始不透明且扩散距离为0
  alphas.add(255);
  spreadRadius.add(0);
  spreadPaint = new Paint();
  spreadPaint.setAntiAlias(true);
  spreadPaint.setAlpha(255);
  spreadPaint.setColor(spreadColor);
}

@Override
protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  for (int i = 0; i < spreadRadius.size(); i++) {
    int alpha = alphas.get(i);
    spreadPaint.setAlpha(alpha);
    int width = spreadRadius.get(i);
    //绘制扩散的圆
    canvas.drawCircle(centerX, centerY, radius + width, spreadPaint);
    //每次扩散圆半径递增，圆透明度递减
    if (alpha   0 && width < 300) {
      alpha = alpha - distance   0 ? alpha - distance : 1;
      alphas.set(i, alpha);
      spreadRadius.set(i, width + distance);
    }
  }
  //当最外层扩散圆半径达到最大半径时添加新扩散圆
  if (spreadRadius.get(spreadRadius.size() - 1)   maxRadius) {
    spreadRadius.add(0);
    alphas.add(255);
  }
  //超过8个扩散圆，删除最先绘制的圆，即最外层的圆
  if (spreadRadius.size()  = 8) {
    alphas.remove(0);
    spreadRadius.remove(0);
  }
  //中间的圆
  canvas.drawCircle(centerX, centerY, radius, centerPaint);
  //延迟更新，达到扩散视觉差效果
  postInvalidateDelayed(delayMilliseconds);
}

<com.example.louliang.spread.SpreadView
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  app:spread_center_color="@color/colorAccent"
  app:spread_delay_milliseconds="35"
  app:spread_distance="5"
  app:spread_max_radius="90"
  app:spread_radius="150"
  app:spread_spread_color="@color/colorAccent" /