This is a common problem, you can not reach the context first and therefore it is null. What you need to do here is that if you use "ActivityName.this" instead of getApplicationContext(), context etc. your problem will be resolved.

UnabletoAddWindow.java

/*
This is a common problem, you can not reach the context first and therefore it is null. 
What you need to do here is that if you use "ActivityName.this" instead of getApplicationContext(),
context etc. your problem will be resolved.
*/
//For example Alert Dialog;
AlertDialog.Builder alertDialog = new AlertDialog.Builder(MainActivity.this); //Activity name
        alertDialog.setMessage("Test Messages");
        alertDialog.setPositiveButton("OK", listener);
        AlertDialog alert = alertDialog.create();
        alert.show();