<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"> 
  <translate 
    android:fromXDelta="0" 
    android:toXDelta="0" 
    android:fromYDelta="120" 
    android:toYDelta="0" 
    android:duration="500" /> 
</set>

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"> 
  <translate 
    android:fromXDelta="0" 
    android:toXDelta="0" 
    android:fromYDelta="0" 
    android:toYDelta="120" 
    android:duration="500" /> 
</set>
PopupWindow的动画显示效果是通过setAnimationStyle(int id)方法设置的，其中id为一个style的id，所以我们要在styles.xml文件中设置一个动画样式：
<style name="popwin_anim_style">
   <item name="android:windowEnterAnimation">@anim/menushow</item>
   <item name="android:windowExitAnimation">@anim/menuhide</item>
</style>

PopupWindow pop = new PopupWindow(view, ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
pop.setAnimationStyle(R.style.popwin_anim_style);