AsyncTask not working with ProgressDialog in android

i am downloading data from website using asynctask and my code for async task is below

public class getSyncTaskInBackground extends AsyncTask<Void, Void, Void>{
    @Override
    protected Void doInBackground(Void... params) {
        getSynchronizeTask();
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {

        if(progressDialog != null && progressDialog.isShowing()) {
            progressDialog.dismiss();
        }
        displaySynchronizetask();
        super.onPostExecute(result);
    }

    @Override
    protected void onPreExecute() {
        progressDialog = ProgressDialog.show(synchronize.this, "Tasks are synchroning...", "Please wait...");
        super.onPreExecute();
    }

    @Override
    protected void onCancelled() {
        super.onCancelled();
        if(progressDialog != null && progressDialog.isShowing()) {
            progressDialog.dismiss();
        }
    }

}

this thread takes more time to complete task so if i want to cancel this thr开发者_运维知识库ead in between of process then i had write this code of back button pressed or if progressbar is already dismiss then i want to close activity by calling finish(); my code for back button is as below

@Override
public void onBackPressed() { 
    syncThread.cancel(true); //syncThread is the object of getSyncTaskInBackground
if(progressDialog != null && progressDialog.isShowing()) {
    progressDialog.dismiss();
} else {
    finish();   
}
}

Now when i pressed back button then the progressdialog is not dismiss is any mistake in mycode ? is any way to complete my need ? please help me

Hi
You might want to call setCancelable with true on your progressDialog instance : http://developer.android.com/reference/android/app/Dialog.html#setCancelable(boolean)

If you want an event on the cancelation of your progressDialog
you can set an onCancelListener http://developer.android.com/reference/android/app/Dialog.html#setOnCancelListener(android.content.DialogInterface.OnCancelListener)

hope this helps