How to change progressDialog text

Question

I have an asynctask but if I implement a Thread.Sleep, then my app crashes, and I don't know why. In onPreExecute I can see my first message and then after two seconds it appears the other one I put in doInBackground, but it's not working.

private class sendMail extends AsyncTask<Void, Void, Void> {

        protected void onPreExecute() {
            dialog.setMessage("Please wait...");
            dialog.show();

        }

        // automatically done on worker thread (separate from UI thread)
        @Override
        protected Void doInBackground(Void... voids) {
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            dialog.setMessage("Downloading files...");

            new BackgroundTask().execute();

//MY DOWNLOADING METHODS STUFF

And then I dismiss this dialog somewhere else.

Log:

An error occurred while executing doInBackground()

Answer 1

You cannot access the UI elements from a background thread you can update the progressbar in onProgressUpdate, most importantly you need to publishProgress(value) in doInBackground and update using onProgressUpdate. Read more about the AsyncTask here.

Example code:

class MyTask extends AsyncTask<Integer, Integer, String> {
        @Override
        protected String doInBackground(Integer... params) {
            for (; count <= params[0]; count++) {
                try {
                    Thread.sleep(1000);
                    publishProgress(count);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            return "Task Completed.";
        }
        @Override
        protected void onPostExecute(String result) {
            progressBar.setVisibility(View.GONE);
                txt.setText(result);
                btn.setText("Restart");
        }
        @Override
        protected void onPreExecute() {
            txt.setText("Task Starting...");
        }
        @Override
        protected void onProgressUpdate(Integer... values) {
            txt.setText("Running..."+ values[0]);
            progressBar.setMessage("Downloading files...");
            progressBar.setProgress(values[0]);
        }
    }