Question

I am working on Android AsyncTask, I wish to make a progress bar during my program is loading. Here’s how I make it.

A class is declared here...
private ArrayList<String> result1 = new ArrayList<String>(); //class variable

onCreate()
{
    Some stuff here...
    new ATask().execute();
     for (int i = 0; i <result1.size();i++)
    {
        output = output +result1.get(i) + "\n\n";
    }
    textView.setText(output);
}
private void do0()
{
    ArrayList<Sentence> result = new ArrayList<Sentence>();
    ArrayList<String> result2 = new ArrayList<String>();
    result = do1("link", true); //just some function I am working
    result1 = do2(result,10);//do2 return ArrayList<String>
}
private class ATask extends AsyncTask<String, Void, String>{
    private ProgressDialog progress = null;
    @Override
    protected String doInBackground(String... params) {
        do0();
        return null;
    }

    @Override
    protected void onCancelled() {
        super.onCancelled();
    }

    @Override
    protected void onPostExecute(String result) {
        progress.dismiss();

        //adapter.notifyDataSetChanged();

        super.onPostExecute(result);
    }

    @Override
    protected void onPreExecute() {
        progress = new ProgressDialog(ReadWebPage.this);

        progress.setMessage("Doing...");
        progress.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        progress.show();

        super.onPreExecute();
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
    }
};

My intention is that, while the progress bar is loading, it will finish the do0() and modify result1, then my oncreate can use that result1 to display in it’s TextView. However my TextView is always empty in this setting. So I move the

     for (int i = 0; i <result1.size();i++)
    {
        output = output +result1.get(i) + "\n\n";
    }
    textView.setText(output);

into the do0() (right after the result1 = do2()), but then the program will crash. I am not familiar with these thread settings, thanks for your help in advance.

Answer 1

You’ll be better served with a thread that holds a Handler object that was initialized on the main thread. Using the handler, you can post() little snippets to be executed on a main thread – like update a progress bar. You can do the same Handler trick from the AsyncTask, but IMHO threads are cleaner.

Said snippets should be implemented as Runnables. Feel free to use a nested anonymous class one-liner.