blog of faywong

mView是我们期望有动画效果的目标View

FrameLayout.LayoutParams mParams = ... // 我们的目标 layout params
if (mTransitionTime > 0) {
    ValueAnimator widthAnim = ValueAnimator.ofInt(0, mParams.width); // 从0变化到期望的宽度
    widthAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator valueAnimator) {
            // 在回调里我们踩着节拍来修改 view 的 layout params
            int val = (Integer) valueAnimator.getAnimatedValue();
            mParams.width = val;
            if (mView != null) {
                mView.setLayoutParams(mParams);
            }
        }
    });
    widthAnim.setDuration(mTransitionTime);
    widthAnim.start();

    ValueAnimator heightAnim = ValueAnimator.ofInt(0, mParams.height); // 从0变化到期望的高度
    heightAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator valueAnimator) {
            // 在回调里我们踩着节拍来修改 view 的 layout params
            int val = (Integer) valueAnimator.getAnimatedValue();
            mParams.height = val;
            if (mView != null) {
                mView.setLayoutParams(mParams);
            }
        }
    });
    heightAnim.setDuration(mTransitionTime);
    heightAnim.start();
}

if (mTransformDegree > 0) { // 如果需要，在由小变大的过程中添加旋转效果
    ObjectAnimator.ofFloat(mView, "rotation", 0f, mTransformDegree * 1.0f)
            .setDuration(mTransitionTime > 0 ? mTransitionTime : 0).start();
}