BackgroundDrawableSwitchCompat.java 文件源码

private void startAnimation(boolean firstToSecond) {
        if (animator != null) {
            animator.cancel();
        }
        animator = ValueAnimator.ofInt(firstToSecond ? OPAQUE : TRANSPARENT, firstToSecond ? TRANSPARENT : OPAQUE);
        animator.setDuration(THUMB_ANIMATION_DURATION);
        animator.setInterpolator(new LinearInterpolator());
//        animator.setRepeatMode(ValueAnimator.RESTART);
//        animator.setRepeatCount(ValueAnimator.INFINITE);

        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                mFirstDrawableAlpha = (int) animation.getAnimatedValue();
                mSecondDrawableAlpha = OPAQUE - (int) animation.getAnimatedValue();
                invalidate();
            }
        });

        animator.start();
    }