从AsyncTask访问TextView（在一个片段内）

Question

Firstly, i'm new to android programming, so sorry if this seems like a silly question, i'm still trying ot get my head around it all! I am trying to update a TextView in a fragment from within my onPostExecute() AsyncTask. But i'm struggling on how to get a TextView from the layout and update it. I seem to be able to create the TextView on the fly and update it, but I wanted to a textview that i've created in my xml layout. I have seen loads of similar questions here, but none are using fragments (its the fragment bit i'm trying to learn).

You can see from the code below, that I tried at first to create the TextView (tv) in the code (commented out) and that worked fine. Then I tried to get the TextView from the layout ((TextView)rootView.findViewById(R.id.tv2)), but because I cannot declare it as a public string, I now don't have access to it in the onPostExecute().

Am i doing something really silly here??

public static class PlaceholderFragment extends Fragment {
    String str;
    //public TextView tv;
    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_tug_boat_main,
                container, false);

        tv = (TextView)rootView.findViewById(R.id.tv2);
        //tv = new TextView(container.getContext());
        tv.setText("hi there");
        ReadExtPortfolio rext = new ReadExtPortfolio();
        rext.execute();
        return tv;
        //return rootView;

    }

    class ReadExtPortfolio extends AsyncTask<Void, Void, Void>
    {
        @Override
        protected void onPreExecute() {
            tv.setText("Fetching data, please wait: ");
        }
        @Override
        protected Void doInBackground(Void... arg0) {
            try {

                 URL url = new URL("http://mywebsite.com/andy.txt");
                 BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
                 str = in.readLine();
                 in.close();
               } catch (IOException e) {
                  str = "error";
                }
            return null;
        }

        // Executed on the UI thread after the
        // time taking process is completed
        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            tv.setText("Completed the task, and the result is : " + str);
        }
    }   
}

XML file (fragment_tug_boat_main) contains...

 <TextView
    android:id="@+id/tv2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/hello_world2" />

Also, I've used stackoverflow for years and the people who answer have saved me hours and hours of work over those years. So thanks for reading this and thanks to everyone who answers.

EDIT: sorry, i should have said. If i uncomment "public TextView tv;" then I get a runtime error: The specified child already has a parent. You must call removeView() on the childs parent first. I didn't think that calling removeView() sounded right as removeView does not exist on my TextView

Answer 1

All you have to do is to uncomment //public TextView tv; and then you will be able to use it in the onPostExecute method.