Alert Dialog and ASync Task

Question

i am trying to use Alert Dialog Box and Async Task in the activity and am getting the following error

Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

Code:

public class loginTask extends AsyncTask<Void, Void, Void> {
    public ProgressDialog loginDialog = new ProgressDialog(
            LoginActivity.this);

    @Override
    protected void onPreExecute() {
        loginDialog.setMessage("Please wait Logging in");
        loginDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {

        if(loginUser()) {
            loginDialog.dismiss();
            alertbox("title", "winnn", "Okay");
        } else {
            loginDialog.dismiss();
            alertbox("title", "message", "Okay");
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void unused) {
        loginDialog.dismiss();
        Intent intentHome = new Intent(LoginActivity.this,
                HomeActivity.class);
        startActivity(intentHome);
    }
}

Paresh Mayani · Accepted Answer · 2011-11-24T13:38:36.130

10

You can't update UI inside the doInBackground() method directly. (Yes if you still want to execute then write the same inside the runOnUiThread() method inside the doInBackground())

Otherwise, do it inside the onPostExecute() method.

public class loginTask extends AsyncTask<Void, Void, Void> 
{
    public ProgressDialog loginDialog = new ProgressDialog( LoginActivity.this );
    public Boolean flag;

    @Override
    protected void onPreExecute() {
        loginDialog.setMessage("Please wait Logging in");
        loginDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {
        if(loginUser())
          flag = true;
        else 
          flag=false;

        return null;
    }

    @Override
    protected void onPostExecute(Void unused) {
        loginDialog.dismiss();

        if(flag)
          alertbox("title", "winnn", "Okay");
        else
          alertbox("title", "message", "Okay");
    }
}

edited Nov 24 '11 at 13:38

answered Nov 24 '11 at 13:28

Paresh Mayani

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"You can't update UI inside the doInBackground() method." We can update inside the doInBackground() using runOnUiThread(). – Lalit Poptani Nov 24 '11 at 13:34
@LalitPoptani its already mentioned in answer before your comment :) – Paresh Mayani Nov 24 '11 at 13:35
@PareshMayani ... what will happend if i use this code and i will change orientation when dialog is showing ? – Selvin Nov 24 '11 at 13:41
@Selvin its different question, for that you need to write `android:configChanges="orientation|keyboardHidden"` inside the AndroidManifest.xml file. – Paresh Mayani Nov 24 '11 at 13:56

score 1 · Answer 2 · answered Nov 24 '11 at 13:33

the onPreexecute and onPostExecute are part of the UI parts in the Async Task.. the doInBackground is a seperate thread so any thing done inside the doInBackground needs to be handled in the form of progressUpdate

 private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
     protected Long doInBackground(URL... urls) {
         int count = urls.length;
         long totalSize = 0;
         for (int i = 0; i < count; i++) {
             totalSize += Downloader.downloadFile(urls[i]);
             publishProgress((int) ((i / (float) count) * 100));
         }
         return totalSize;
     }

     protected void onProgressUpdate(Integer... progress) {
         setProgressPercent(progress[0]);
     }

     protected void onPostExecute(Long result) {
         showDialog("Downloaded " + result + " bytes");
     }
 }

Example Reference: Link

reflects any changes you need to make to the UI inbetween the doInBackground process.

He is facing problem for showing dialog from doInBackground(). — Paresh Mayani, Nov 24 '11 at 13:36
yeah your answer seems good so i have no worries. intentions solved right — medampudi, Nov 24 '11 at 13:37

Alert Dialog and ASync Task

2 Answers2

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