概述

我看到很多以幻灯片方式打开的动画，通常，这是要更改的视图的实际布局，然而，如果您只是改变高度，它将只是在闪烁。我给你们展示两种方法来实现这个动画。

ValueAnimation

第一种方法是使用ValueAnimation (可以在AnimatorSet中使用)，这个动画会改变设置属性的值，并沿着抛物线(或者任何你专门设置进插值器的线方程)，然后转到它的每个点，然后让你创建一个方程，基于该行上的动画在哪个位置。

 

//view we want to animate
final View messageView = view.findViewById(R.id.message_section);

//set the values we want to animate between and how long it takes
//to run
ValueAnimator slideAnimator = ValueAnimator
 . ofInt(currentHeight, newHeight)
 . setDuration(300);


//we want to manually handle how each tick is handled so add a
//listener
slideAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
 @Override
 public void onAnimationUpdate(ValueAnimator animation) {
 //get the value the interpolator is at
 Integer value = (Integer) animation.getAnimatedValue();
 //I'm going to set the layout's height 1:1 to the tick
 messageView.getLayoutParams().height = value.intValue();
 //force all layouts to see which ones are affected by
 //this layouts height change
 messageView.requestLayout();
 }
});

//create a new animationset
AnimatorSet set = new AnimatorSet();
//since this is the only animation we are going to run we just use
//play
set.play(slideAnimator);
//this is how you set the parabola which controls acceleration
set.setInterpolator(new AccelerateDecelerateInterpolator());
//start the animation
set.start();

自定义动画效果

另外一个更为极端的解决方案，就是创建一个扩展Animation，它似乎不总是按你想要的方式工作，这比上面的ValueAnimator要灵活得多，而且工作几乎完全一样，你可以使构造函数采用新的高度和旧的高度。这也使用了插值器，所以，你仍然可以设置一个自定义方程，下面是一个基本示例：

 

public class SlideAnimation extends Animation {

 int mFromHeight;
 int mToHeight;
 View mView;

 public SlideAnimation(View view, int fromHeight, int toHeight) {
 this.mView = view;
 this.mFromHeight = fromHeight;
 this.mToHeight = toHeight;
 }

 @Override
 protected void applyTransformation(float interpolatedTime, Transformation transformation) {
 int newHeight;

 if (mView.getHeight()!= mToHeight) {
 newHeight = (int) (mFromHeight + ((mToHeight - mFromHeight) * interpolatedTime));
 mView.getLayoutParams().height = newHeight;
 mView.requestLayout();
 }
 }

 @Override
 public void initialize(int width, int height, int parentWidth, int parentHeight) {
 super.initialize(width, height, parentWidth, parentHeight);
 }

 @Override
 public boolean willChangeBounds() {
 return true;
 }
}

以上几乎完全相同，但是，你必须在某处使用它，所以，看起来像这样，

 

View messageView = view.findViewById(R.id.message_section);

Animation animation = new SlideAnimation(messageView, currentHeight, newHeight);

//this interpolator only speeds up as it keeps going
animation.setInterpolator(new AccelerateInterpolator());
animation.setDuration(300);
messageView.setAnimation(animation);
messageView.startAnimation(animation);

结束语

这两种方法都可以获得相同的结果，并且可以构建。注意，它并非总是在所有地方工作，当我制作这个自定义动画类时，当我在一个抽屉中使用它时它不能工作，但是，ValueAnimator 可以.

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