Question

I need to fill the ListView with AsyncTask.
This code works, the TextView changes to “Begin”, then “End”. But the ListView is blank, not showing. In the log I see “array = 3”.

package a.test3;

import java.util.ArrayList;

import a.test3.MainActivity;
import a.test3.R;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends Activity {

    GrabURL mt;
    TextView textView;
    ListView lvMain;
    ArrayList<String> result_arr = new ArrayList<String>();

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = new TextView(this);
        lvMain = (ListView) findViewById(R.id.listView1);

        mt = new GrabURL();
        mt.execute();
    }

    public class GrabURL extends AsyncTask<Void, Void, ArrayList<String>> {             
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            textView.setText("Begin");
            setContentView(textView);
        }

        @Override
        protected ArrayList<String> doInBackground(Void... params) {
            result_arr.add("a");
            result_arr.add("b");
            result_arr.add("c");
            return result_arr;
        }

        @Override
        protected void onPostExecute(ArrayList<String> result) {
            super.onPostExecute(result);

            Log.d("info", "array = " + result.size());

            textView.setText("End");
            setContentView(textView);

            ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this,
                    android.R.layout.simple_list_item_1, result);
            lvMain.setAdapter(adapter);
        }
    }
}

Tell me, please, what am I doing wrong?

Answer 1

Look at your code

        textView.setText("End");
        setContentView(textView);

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this,
                android.R.layout.simple_list_item_1, result_arr);
        lvMain.setAdapter(adapter);

You set View (layout) for your activity. You only display TextView here setContentView(textView);. There’s no ListView lvMain; in your ContentView when you set TextView as a ContentView for your Activity.

Delete this line

setContentView(textView);

If it still isn’t working add

textView.invalidate();