Here lies your problem:
private void fillTextView (int id, String text) {
TextView tv = (TextView) findViewById(id);
tv.setText(text); // tv is null
}
--> (TextView) findViewById(id); // returns null But from your code, I can't find why this method returns null. Try to track down, what id you give as a parameter and if this view with the specified id exists.
The error message is very clear and even tells you at what method. From the documentation:
public final View findViewById (int id)
Look for a child view with the given id. If this view has the given id, return this view.
Parameters
id The id to search for.
Returns
The view that has the given id in the hierarchy or null
http://developer.android.com/reference/android/view/View.html#findViewById%28int%29
In other words: You have no view with the id you give as a parameter.