"android.view.WindowManager$BadTokenException: Unable to add window" on buider.show()

Question

From my main activity, I need to call an inner class and in a method within the class, I need to show AlertDialog. After dismissing it, when the OK button is pressed, forward to Google Play for purchase.

Things work perfectly for most of the times, but for few users it is crashing on builder.show() and I can see "android.view.WindowManager$BadTokenException: Unable to add window" from crash log. Please suggest.

My code is pretty much like this:

public class classname1 extends Activity{

  public void onCreate(Bundle savedInstanceState) {
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.<view>); 

    //call the <className1> class to execute
  }

  private class classNamename2 extends AsyncTask<String, Void, String>{

    protected String doInBackground(String... params) {}

    protected void onPostExecute(String result){
      if(page.contains("error")) 
      {
        AlertDialog.Builder builder = new AlertDialog.Builder(classname1.this);
        builder.setCancelable(true);
        builder.setMessage("");
        builder.setInverseBackgroundForced(true);
        builder.setNeutralButton("Ok",new DialogInterface.OnClickListener() {
          public void onClick(DialogInterface dialog, int whichButton){
            dialog.dismiss();
            if(!<condition>)
            {
              try
              {
                String pl = ""; 

                mHelper.<flow>(<class>.this, SKU, RC_REQUEST, 
                  <listener>, pl);
              }

              catch(Exception e)
              {
                e.printStackTrace();
              }
            }  
          }
        });

        builder.show();
      }
    }
  }
}

I have also seen the error in another alert where I am not forwarding to any other activity. It's simple like this:

AlertDialog.Builder builder = new AlertDialog.Builder(classname1.this);
    builder.setCancelable(true);

    //if successful
    builder.setMessage(" ");
    builder.setInverseBackgroundForced(true);
    builder.setNeutralButton("Ok",new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int whichButton){
            // dialog.dismiss();
                   }
    });
    builder.show();
}

Answer 1

android.view.WindowManager$BadTokenException: Unable to add window"

Problem :

This exception occurs when the app is trying to notify the user from the background thread (AsyncTask) by opening a Dialog.

If you are trying to modify the UI from background thread (usually from onPostExecute() of AsyncTask) and if the activity enters finishing stage i.e.) explicitly calling finish(), user pressing home or back button or activity clean up made by Android then you get this error.

Reason :

The reason for this exception is that, as the exception message says, the activity has finished but you are trying to display a dialog with a context of the finished activity. Since there is no window for the dialog to display the android runtime throws this exception.

Solution:

Use isFinishing() method which is called by Android to check whether this activity is in the process of finishing: be it explicit finish() call or activity clean up made by Android. By using this method it is very easy to avoid opening dialog from background thread when activity is finishing.

Also maintain a weak reference for the activity (and not a strong reference so that activity can be destroyed once not needed) and check if the activity is not finishing before performing any UI using this activity reference (i.e. showing a dialog).

eg.

private class chkSubscription extends AsyncTask<String, Void, String>{

  private final WeakReference<login> loginActivityWeakRef;

  public chkSubscription (login loginActivity) {
    super();
    this.loginActivityWeakRef= new WeakReference<login >(loginActivity)
  }

  protected String doInBackground(String... params) {
    //web service call
  }

  protected void onPostExecute(String result) {
    if(page.contains("error")) //when not subscribed
    {
      if (loginActivityWeakRef.get() != null && !loginActivityWeakRef.get().isFinishing()) {
        AlertDialog.Builder builder = new AlertDialog.Builder(login.this);
        builder.setCancelable(true);
        builder.setMessage(sucObject);
        builder.setInverseBackgroundForced(true);

        builder.setNeutralButton("Ok",new DialogInterface.OnClickListener() {
          public void onClick(DialogInterface dialog, int whichButton){
            dialog.dismiss();
          }
        });

        builder.show();
      }
    }
  }
}

Update :

Window Tokens:

As its name implies, a window token is a special type of Binder token that the window manager uses to uniquely identify a window in the system. Window tokens are important for security because they make it impossible for malicious applications to draw on top of the windows of other applications. The window manager protects against this by requiring applications to pass their application's window token as part of each request to add or remove a window. If the tokens don't match, the window manager rejects the request and throws a BadTokenException. Without window tokens, this necessary identification step wouldn't be possible and the window manager wouldn't be able to protect itself from malicious applications.

?A real-world scenario:

When an application starts up for the first time, the?ActivityManagerService?creates a special kind of window token called an application window token, which uniquely identifies the application's top-level container window.?The activity manager gives this token to both the application and the window manager, and the application sends the token to the window manager each time it wants to add a new window to the screen. This ensures secure interaction between the application and the window manager (by making it impossible to add windows on top of other applications), and also makes it easy for the activity manager to make direct requests to the window manager.