Android中模仿抖音加载框之两颗小球转动效果

 @BindView(R.id.dy1)
 DYLoadingView dy1;
 @OnClick(R.id.b1)
 void start() {
 dy1.setXXXXX; //设置属性(可选）
 dy1.start(); //开始动画
 }
 @OnClick(R.id.b2)
 void stop() {
 dy1.stop(); //停止动画
 }

 private void initAnim() {
 fraction = 0.0f;
 stop();
 anim = ValueAnimator.ofFloat(0.0f, 1.0f);
 anim.setDuration(duration);
 if (pauseDuration > 0) {
  anim.setStartDelay(pauseDuration);
  anim.setInterpolator(new AccelerateDecelerateInterpolator());
 } else {
  anim.setRepeatCount(ValueAnimator.INFINITE);
  anim.setRepeatMode(ValueAnimator.RESTART);
  anim.setInterpolator(new LinearInterpolator());
 }
 anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
  @Override
  public void onAnimationUpdate(ValueAnimator animation) {
  fraction = animation.getAnimatedFraction();
  invalidate();
  }
 });
 anim.addListener(new AnimatorListenerAdapter() {
  @Override
  public void onAnimationStart(Animator animation) {
  isLtr = !isLtr;
  }
  @Override
  public void onAnimationRepeat(Animator animation) {
  isLtr = !isLtr;
  }
  @Override
  public void onAnimationCancel(Animator animation) {
  isAnimCanceled = true;
  }
  @Override
  public void onAnimationEnd(Animator animation) {
  if (!isAnimCanceled) {
   anim.start();
  }
  }
 });
 }

float ltrX = getMeasuredWidth() / 2.0f - distance / 2.0f;
ltrX = ltrX + (distance * fraction);
float rtlX = getMeasuredWidth() / 2.0f + distance / 2.0f;
rtlX = rtlX - (distance * fraction);

ltrBallRadius = ltrInitRadius * (1 + (ltrScale - 1) * scaleFraction);
rtlBallRadius = rtlInitRadius * (1 + (rtlScale - 1) * scaleFraction);

@Override
 protected void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 float centerY = getMeasuredHeight() / 2.0f;
 float ltrInitRadius, rtlInitRadius;
 Paint ltrPaint, rtlPaint;
 //确定当前【从左往右】移动的是哪颗小球
 if (isLtr) {
  ltrInitRadius = radius1;
  rtlInitRadius = radius2;
  ltrPaint = paint1;
  rtlPaint = paint2;
 } else {
  ltrInitRadius = radius2;
  rtlInitRadius = radius1;
  ltrPaint = paint2;
  rtlPaint = paint1;
 }
 float ltrX = getMeasuredWidth() / 2.0f - distance / 2.0f;
 ltrX = ltrX + (distance * fraction);//当前从左往右的球的X坐标
 float rtlX = getMeasuredWidth() / 2.0f + distance / 2.0f;
 rtlX = rtlX - (distance * fraction);//当前从右往左的球的X坐标
 //计算小球移动过程中的大小变化
 float ltrBallRadius, rtlBallRadius;
 if (fraction <= scaleStartFraction) { //动画进度[0,scaleStartFraction]时，球大小由1倍逐渐缩放至ltrScale/rtlScale倍
  float scaleFraction = 1.0f / scaleStartFraction * fraction; //百分比转换 [0,scaleStartFraction]] -> [0,1]
  ltrBallRadius = ltrInitRadius * (1 + (ltrScale - 1) * scaleFraction);
  rtlBallRadius = rtlInitRadius * (1 + (rtlScale - 1) * scaleFraction);
 } else if (fraction >= scaleEndFraction) { //动画进度[scaleEndFraction,1]，球大小由ltrScale/rtlScale倍逐渐恢复至1倍
  float scaleFraction = (fraction - 1) / (scaleEndFraction - 1); //百分比转换，[scaleEndFraction,1] -> [1,0]
  ltrBallRadius = ltrInitRadius * (1 + (ltrScale - 1) * scaleFraction);
  rtlBallRadius = rtlInitRadius * (1 + (rtlScale - 1) * scaleFraction);
 } else { //动画进度[scaleStartFraction,scaleEndFraction]，球保持缩放后的大小
  ltrBallRadius = ltrInitRadius * ltrScale;
  rtlBallRadius = rtlInitRadius * rtlScale;
 }
 ltrPath.reset();
 ltrPath.addCircle(ltrX, centerY, ltrBallRadius, Path.Direction.CW);
 rtlPath.reset();
 rtlPath.addCircle(rtlX, centerY, rtlBallRadius, Path.Direction.CW);
 mixPath.op(ltrPath, rtlPath, Path.Op.INTERSECT);
 canvas.drawPath(ltrPath, ltrPaint);
 canvas.drawPath(rtlPath, rtlPaint);
 canvas.drawPath(mixPath, mixPaint);
 }