我的应用程序在Android版本2.3.3上运行良好，但在android 4.2.2上无法运行

Question

Here is the JAVA code of my app:

public class Main extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    new GetUrl().execute(20);

}
private class GetUrl extends AsyncTask<Integer, Integer, BufferedReader> {

    @Override
    protected BufferedReader doInBackground(Integer... params) {
        BufferedReader reader = null;
        try {
            URL url = null;
            url = new URL("http://www.google.com");
            URLConnection conn = url.openConnection();
            reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

        }
        catch (Exception e) {
            TextView tv = (TextView) findViewById(R.id.textView1);
            tv.setText("Error");
        }
        return reader;
    } 
    @Override
    protected void onPostExecute(BufferedReader reader) {
        TextView tv = (TextView) findViewById(R.id.textView1);
        String line = null;

        try {
            line = reader.readLine().toString();    /*This line if removed removes the error. Whenever i try to work with the reader, it stops working for 4.2.2 but works fine for 2.3.3*/
            tv.setText(line);


        }
        catch( Exception e) {
            tv.setText(e.getMessage());
        }

    }

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

}

Whenever i try to work with the reader, it stops working for 4.2.2 but works fine for 2.3.3. I posted a similar question before and i was asked to solve the problem using asyncTask, but that didn't really help me out.

Answer 1

You should only be accessing the reader in the doInBackground method, which executes on a background thread.

The onPostExecute method runs on the UI thread, and should only update the UI, not do any other work.

So, I'd suggest changing your AsyncTask to

AsyncTask<Integer, Integer, String> 

move the line

reader.readLine().toString();

to onPostExecute, return the string from doInBackground, and make the parameter to onPostExecute the string that you read.