[android] Android runOnUiThread explanation

I am trying to display a progress dialog during the onCreate() method of one of my activities, have the work done to populate the screen done in a thread, and then dismiss the progress dialog.

Here is my onCreateMethod()

dialog = new ProgressDialog(HeadlineBoard.this);
        dialog.setMessage("Populating Headlines.....");
        dialog.show();
        populateTable();

The populateTable method contains my thread and the code to dismiss the dialog, but for some reason. The activity comes up blank for about 10 secs(doing the populateTable() work), and then I see the screen. I never see the dialog displayed, any ideas?

Here is the populateTable() code:

//Adds a row to the table for each headline passed in
private void populateTable() {
    new Thread() {
        @Override
        public void run() {
            //If there are stories, add them to the table
            for (Parcelable currentHeadline : allHeadlines) {
                addHeadlineToTable(currentHeadline);
            }
               try {
                     // code runs in a thread
                     runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                dialog.dismiss();
                            }
                     });
               } catch (final Exception ex) {
                   Log.i("---","Exception in thread");
               }
        }
 }.start();

}

This should work for you

 public class MyActivity extends Activity {

    protected ProgressDialog mProgressDialog;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        populateTable();
    }

    private void populateTable() {
        mProgressDialog = ProgressDialog.show(this, "Please wait","Long operation starts...", true);
        new Thread() {
            @Override
            public void run() {

                doLongOperation();
                try {

                    // code runs in a thread
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            mProgressDialog.dismiss();
                        }
                    });
                } catch (final Exception ex) {
                    Log.i("---","Exception in thread");
                }
            }
        }.start();

    }

    /** fake operation for testing purpose */
    protected void doLongOperation() {
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
        }

    }
}

Instead of creating a thread, and using runOnUIThread, this is a perfect job for ASyncTask:

• In onPreExecute, create & show the dialog.

• in doInBackground prepare the data, but don't touch the UI -- store each prepared datum in a field, then call publishProgress.

• In onProgressUpdate read the datum field & make the appropriate change/addition to the UI.

• In onPostExecute dismiss the dialog.

If you have other reasons to want a thread, or are adding UI-touching logic to an existing thread, then do a similar technique to what I describe, to run on UI thread only for brief periods, using runOnUIThread for each UI step. In this case, you will store each datum in a local final variable (or in a field of your class), and then use it within a runOnUIThread block.