Exception

Question

What should i look for when i get an exception like this?
Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference.
I think there might be something wrong with this part from one of my activities, because it is some of the newest i have build in the activity.
public QuestionsActivity(){
        mFirstTextView = (TextView) findViewById(R.id.questionText);
        mFirstTextView.setText("Am I a question?");
The meaning is that when the activity get started then some text should appear in a textview.
I hope someone understand my question.
Thank you for your time
thoughts from here

Seth Kroger · Accepted Answer

"Attempt to invoke virtual method ... on a null object reference." happens because something wasn't initialized properly and was left as null.  In Android, you'll often need system resources, such as context and the layout engine to initialize things properly. This is done later than the constructor call, so it's impossible to get a meaningful value to initialize a view with.
That's why as a matter of practice you should never use a constructor to setup an activity, but always use the lifecycle methods like onCreate() instead.

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Mark Junge

Mark Junge

Exception

What should i look for when i get an exception like this?

Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference.

1 Answer

Seth Kroger

Seth Kroger

Mark Junge

Mark Junge