Can't create handler inside thread that has not called Looper.prepare() inside AsyncTask for ProgressDialog

Question

I don't understand why I'm getting this error. I'm using AsyncTask to run some processes in the background.

I have:

protected void onPreExecute() 
{
    connectionProgressDialog = new ProgressDialog(SetPreference.this);
    connectionProgressDialog.setCancelable(true);
    connectionProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
    connectionProgressDialog.setMessage("Connecting to site...");
    connectionProgressDialog.show();

    downloadSpinnerProgressDialog = new ProgressDialog(SetPreference.this);
    downloadSpinnerProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
    downloadSpinnerProgressDialog.setMessage("Downloading wallpaper...");
}

When I get into doInBackground() depending on a condition I:

[...]    
connectionProgressDialog.dismiss();
downloadSpinnerProgressDialog.show();
[...]

Whenever I try downloadSpinnerProgressDialog.show() I receive the error.

Any ideas guys?

score 106 · Accepted Answer · edited May 23 '17 at 12:30

106

The method show() must be called from the User-Interface (UI) thread, while doInBackground() runs on different thread which is the main reason why AsyncTask was designed.

You have to call show() either in onProgressUpdate() or in onPostExecute().

For example:

class ExampleTask extends AsyncTask<String, String, String> {

    // Your onPreExecute method.

    @Override
    protected String doInBackground(String... params) {
        // Your code.
        if (condition_is_true) {
            this.publishProgress("Show the dialog");
        }
        return "Result";
    }

    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
        connectionProgressDialog.dismiss();
        downloadSpinnerProgressDialog.show();
    }
}

edited May 23 '17 at 12:30

Community

1
1

answered Sep 01 '10 at 03:16

Konstantin Burov

68,980
16
115
93

3

That didn't do the trick for me, just tried "AlertDialog.Builder builder = new AlertDialog.Builder(context);" and added the configuration of the builder. Trying to show this inside the onProgressUpdate leads to exactly the same error. Any ideas ? – ins0m Aug 30 '11 at 21:28
Thanks Konstantin, I didn't realise you could override onProgressUpdate with any variable type using publishProgress(). Really helped me, to simply update with toast messages. – wired00 Dec 12 '12 at 03:07

score 81 · Answer 2 · edited Nov 14 '11 at 15:23

81

I had a similar issue but from reading this question I figured I could run on UI thread:

YourActivity.this.runOnUiThread(new Runnable() {
    public void run() {
        alertDialog.show();
    }
});

Seems to do the trick for me.

edited Nov 14 '11 at 15:23

Octavian Helm

39,405
19
98
102

answered Sep 01 '11 at 12:05

hyui

811
6
3

getActivity().runOnUiThread(this::mymethod); Thanks worked very well. – mortezahosseini Mar 07 '19 at 10:26

score 1 · Answer 3 · answered May 16 '12 at 10:08

I had a hard time making this work too, the solution for me was to use both hyui and konstantin answers,

class ExampleTask extends AsyncTask<String, String, String> {

// Your onPreExecute method.

@Override
protected String doInBackground(String... params) {
    // Your code.
    if (condition_is_true) {
        this.publishProgress("Show the dialog");
    }
    return "Result";
}

@Override
protected void onProgressUpdate(String... values) {

    super.onProgressUpdate(values);
    YourActivity.this.runOnUiThread(new Runnable() {
       public void run() {
           alertDialog.show();
       }
     });
 }

}

I thought stuff done in `onProgressUpdate()` was automatically going to run on the UI thread — Someone Somewhere, Nov 25 '13 at 19:21

score 0 · Answer 4 · answered Mar 28 '12 at 12:13

final Handler handler = new Handler() {
        @Override
        public void handleMessage(final Message msgs) {
        //write your code hear which give error
        }
        }

new Thread(new Runnable() {
    @Override
    public void run() {
    handler.sendEmptyMessage(1);
        //this will call handleMessage function and hendal all error
    }
    }).start();

Can't create handler inside thread that has not called Looper.prepare() inside AsyncTask for ProgressDialog

4 Answers4

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