1.兩個動畫，包括show 和hide

show:

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:fillAfter="true"
    android:fillEnabled="true" >

    <scale
        android:duration="200"
        android:fromXScale="1.0"
        android:fromYScale
 
="0.0"
        android:interpolator="@android:anim/accelerate_decelerate_interpolator"
        android:pivotX="50%"
        android:pivotY="0%"
        android:toXScale="1.0"
        android:toYScale="1.0" >
    </scale>

      <alpha
        android:duration="180"     
        android:fromAlpha="0.0"
 

        android:toAlpha="1.0" />

</set>

hide:

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android" 
    android:fillEnabled="true"
    android:fillAfter="true">

    <scale
        android:duration="200"    
        android:fromXScale
 
="1.0"
        android:fromYScale="1.0"
        android:interpolator="@android:anim/accelerate_interpolator"
        android:pivotX="50%"
        android:pivotY="0%"
        android:toXScale="1.0"
        android:toYScale="0.0" >
    </scale>

    <alpha
        android:duration="180"       
        android:fromAlpha="1.0"
        android:toAlpha="0.0" />

</set>

2.新增動畫樣式:

 <style name="popmenu_animation" parent="android:Animation">
        <item name="android:windowEnterAnimation">@anim/popumenu_animation_show</item>
        <item name="android:windowExitAnimation">@anim/popumenu_animation_hide</item>
    </style>

3.新增動畫

PopupWindow.setAnimationStyle(R.style.popmenu_animation);