Blur or dim background when Android PopupWindow active

The question was about the Popupwindow class, yet everybody has given answers that use the Dialog class. Thats pretty much useless if you need to use the Popupwindow class, because Popupwindow doesn’t have a getWindow() method.

I’ve found a solution that actually works with Popupwindow. It only requires that the root of the xml file you use for the background activity is a FrameLayout. You can give the Framelayout element an android:foreground tag. What this tag does is specify a drawable resource that will be layered on top of the entire activity (that is, if the Framelayout is the root element in the xml file). You can then control the opacity (setAlpha()) of the foreground drawable.

You can use any drawable resource you like, but if you just want a dimming effect, create an xml file in the drawable folder with the <shape> tag as root.

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >
    <solid android:color="#000000" />
</shape>

(See http://developer.android.com/guide/topics/resources/drawable-resource.html#Shape for more info on the shape element).
Note that I didn’t specify an alpha value in the color tag that would make the drawable item transparent (e.g #ff000000). The reason for this is that any hardcoded alpha value seems to override any new alpha values we set via the setAlpha() in our code, so we don’t want that.
However, that means that the drawable item will initially be opaque (solid, non-transparent). So we need to make it transparent in the activity’s onCreate() method.

Here’s the Framelayout xml element code:

<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/mainmenu"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:foreground="@drawable/shape_window_dim" >
...
... your activity's content
...
</FrameLayout>

Here’s the Activity’s onCreate() method:

public void onCreate( Bundle savedInstanceState)
{
  super.onCreate( savedInstanceState);

  setContentView( R.layout.activity_mainmenu);

  //
  // Your own Activity initialization code
  //

  layout_MainMenu = (FrameLayout) findViewById( R.id.mainmenu);
  layout_MainMenu.getForeground().setAlpha( 0);
}

Finally, the code to dim the activity:

layout_MainMenu.getForeground().setAlpha( 220); // dim

layout_MainMenu.getForeground().setAlpha( 0); // restore

The alpha values go from 0 (opaque) to 255 (invisible).
You should un-dim the activity when you dismiss the Popupwindow.

I haven’t included code for showing and dismissing the Popupwindow, but here’s a link to how it can be done: http://www.mobilemancer.com/2011/01/08/popup-window-in-android/