How to close Progress dialog from background

Question

I am kinda new to android and stuck in a situation, where I don't know how to handle it.

Here is what I am trying to do:

From Activity I start some tasks and show Progress-Dialog while the task completes in background. If the task successfully completes I close the Activity and start new Activity.

But if in background I caught an exception I want to go back to the activity and close the Progress-Dialog and show a Toast maybe that some exception has occurred.

From Activity:

@Override
public void onCreate(Bundle savedInstanceState) 
{
 // my code

 // start Progress Dialog
   showProgressDialog();  
}

public void showProgressDialog()
{
   PD =  new ProgressDialog(getActivity());
   PD.setMessage("Downloading.....");
   PD.show();
}

@Override
public void onDestroy()
{
   super.onDestroy();
   if (PD != null) 
   {
      PD.dismiss();
      PD = null;
   }
}

and in background:

try 
{
   // perform some db tasks 
   // using AsyncTask 
}
catch (Exception e) 
{
   if(e.getErrorCode() == 34)
   {
      // From here I want go back to Activity and close the Progress dialog
      // and shows what error has occurred.
   }
}

So if exception occurred how I am suppose to go back to the activity and close that Progress-dialog, or is there any other way to doing this?

Answer 1

As I know ProgressDialog is in your UI thread and you don't access to that in the background thread. Why don't you use AsyncTask instead ? It's easy to use and you can handle it much easier. Example:

class TestAsync extends AsyncTask<Void, Void, Void> {

        private ProgressDialog mDialog;
        private Boolean error = false;

        @Override
        protected void onPreExecute() {

            mDialog = new ProgressDialog(TestActivity.this);
            mDialog.setCancelable(false);
            mDialog.show();

        }

        @Override
        protected Void doInBackground(Void... arg0) {


            try {
                // whatever you would like to do in background
            } catch (Exception e) {
                error = true;
            }

            return null;
        }

        protected void onPostExecute(Void... arg0) {
            mDialog.dismiss();

            if (error) {
                Toast.makeText(getApplicationContext(),
                        R.string.error, Toast.LENGTH_SHORT).show();
                return;
            } else {

                // whatever you would like to do after background 
            } 

        }
    }