SwipeToRefreshLayout.java 文件源码

private Animation startAlphaAnimation(final int startingAlpha, final int endingAlpha) {
    // Pre API 11, alpha is used in place of scale. Don't also use it to
    // show the trigger point.
    if (mScale && isAlphaUsedForScale()) {
        return null;
    }
    Animation alpha = new Animation() {
        @Override
        public void applyTransformation(float interpolatedTime, Transformation t) {
            mProgress
                    .setAlpha((int) (startingAlpha + ((endingAlpha - startingAlpha)
                            * interpolatedTime)));
        }
    };
    alpha.setDuration(ALPHA_ANIMATION_DURATION);
    // Clear out the previous animation listeners.
    mCircleView.setAnimationListener(null);
    mCircleView.clearAnimation();
    mCircleView.startAnimation(alpha);
    return alpha;
}