LayoutInflater inflater = getLayoutInflater();
final View view = inflater.inflate(R.layout.popup, null);

PopupWindow popupWindow = new PopupWindow(view, 400, 400, true);
popupWindow.setBackgroundDrawable(new BitmapDrawable());

showAsDropDown(View anchor)：//相对某个控件的位置（正左下方），无偏移
showAsDropDown(View anchor, int xoff, int yoff)：//相对某个控件的位置，有偏移
showAtLocation(View parent, int gravity, int x, int y)：//相对于父控件的位置（例如正中央Gravity.CENTER，下方Gravity.BOTTOM等），可以设置偏移或无偏移

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">  <scale android:fromXScale="1.0" android:toXScale="1.0"  android:fromYScale="0" android:toYScale="1.0" android:pivotX="50%" android:pivotY="0%"android:duration="100" />
</set>

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">  <scale  android:fromXScale="1.0" android:toXScale="1.0"  android:fromYScale="1.0" android:toYScale="0"  android:pivotX="50%" android:pivotY="0%"  android:duration="50" />
</set>

<style name="PopupAnimation" parent="android:Animation"><item name="android:windowEnterAnimation">@anim/popup_enter</item><item name="android:windowExitAnimation">@anim/popup_exit</item>
</style>

popupWindow.setAnimationStyle(R.style.PopupAnimation);  

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android" ><translateandroid:duration="250"android:fromYDelta="100.0%"android:toYDelta="0.0" />
</set>

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android" ><translateandroid:duration="250"android:fromYDelta="0.0"android:toYDelta="100%" />
</set>

<style name="anim_menu_bottombar"><item name="android:windowEnterAnimation">@anim/menu_bottombar_in</item><item name="android:windowExitAnimation">@anim/menu_bottombar_out</item>
</style>