Question

I have doInBackground(). after function I want to change some TextView on MainActivity.
but When I trigger the function on main activity I got NullPointerException on TextView line.

protected String doInBackground(Object... arguments) {

    some code..

    return result;
}

@Override
protected void onPostExecute(String result) {
    if(result!=null)
        new MainActivity().setScoreListUpdate(result);
}

MainActivity:

public void setScoreListUpdate(String settings)
{
    String[] yeniscore = settings.split("\\|");

    if(yeniscore.length > 1)
    {
            birinci.setText(yeniscore[1]);  << NULLPOINTEREXC.
    }
}

Answer 1

The reason this gives a NullPointerException is that you create a new instance of MainActivity instead of working on your existing one.

What you need to do is pass a reference to your Activity to the AsyncTask and then call your method on that reference.

So in your AsyncTask-class you will have a variable:

private MainActivity myMainActivity;

Add a constructor to your AsyncTask-class:

public MyAsyncTaskClassName( MainActivity activity ) {
    myMainActivity = activity;
}

Then in onPostExecute you do:

myMainActivity.setScoreListUpdate(result);