I've been working on OTA support for PhoneLab testbed. And one problem I encountered is that, when I tried to pop out an AlertDialog to let user confirm update, I get this error that saied something like this:

android.view.WindowManager$BadTokenException: Unable to add window -- token null
is not for an application

Apparently, the context I used to create the dialog, which is the service context, is not valid in the sense that it has not windows attached. Yet create an Activity just to pop out a alert dialog is a bit of overdone, since my app is basically a background service.

Here is how I solved this problem.

  • Add android.permission.SYSTEM_ALERT_WINDOW permission to AndroidManifest.xml
<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
  • After creating the dialog, before show it, set its window type to system alert.
// builder set up code here
// ...

AlertDialog dialog = builder.create();

Ref: stackoverflow thread, another similar post