1. 如何为自定义View添加动画效果

public void startAnimation() {
    ValueAnimator anim = ValueAnimator.ofFloat(minValue, midValue, maxValue);
    anim.setRepeatCount(ValueAnimator.INFINITE);//设置无限重复
    anim.setRepeatMode(ValueAnimator.RESTART);//设置重复模式
    anim.setDuration(1000);
    anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            value = (Float) animation.getAnimatedValue();
            postInvalidate();
        }
    });
    anim.start();
}

即利用ValueAnimator，在动画的duration期间，产生一系列的value值，然后不断刷新来触发View的重绘，重绘过程中用到了这些value值，从而达到了动画效果

2.颜色渐变

int startColor = 0x33FFFFFF;
int endColor = 0xE6FF5800;
GradientDrawable gradient = (GradientDrawable) mButtonLayout.getBackground();
ValueAnimator colorAnim = ValueAnimator.ofObject(new ArgbEvaluator(), startColor, endColor);
// ValueAnimator colorAnim = ValueAnimator.ofArgb(startColor, endColor);
colorAnim.setDuration(3000);
colorAnim.start();
colorAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
  @Override
  public void onAnimationUpdate(ValueAnimator animation) {
    int color = (int) animation.getAnimatedValue();
    gradient.setColor(color);
  }
});