Question

How can i use AsyncTask Class to showing dialog when execute a task???

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

    @Override
    protected void onPreExecute() {
        ProgressDialog.show(???, null, null);
        super.onPreExecute();
    }
    @Override
    protected Void doInBackground(Void... params) {
        // TODO Auto-generated method stub
        return null;
    }

}

Answer 1

Assuming that TestAsyncTask is an inner class to an Activity, then you can use the activity name .this to get the context. If TestAsyncTask is not an inner class, then you will want to pass an instance of your Activity into the constructor so that you can provide it as the Context to the ProgressDialog.show() method.

Here is an example of the inner class method:

class MyActivity extends Activity {
    //Activity Lifecycle methods

    class TestAsynTask extends AsyncTask<Void, Void, Void> {
        ProgressDialog dialog;

        @Override
        protected void onPreExecute() {
            dialog = ProgressDialog.show(MyActivity.this, "title", "message");
            super.onPreExecute();
        }

        @Override
        protected Void doInBackground(Void... params) {
            //very long computation...
            return null;
        }

        @Override
        protected void onPostExecute(Void void) {
           dialog.cancel();
        }
    }
}

You will notice that you should save off the ProgressDialog to a instance variable in the onPreExecute() method and call cancel() on it in the onPostExecute() method.

The other approach looks similar:

class MyActivity extends Activity {
    //Activity Lifecycle methods


}

class TestAsynTask extends AsyncTask<Void, Void, Void> {
    ProgressDialog dialog;
    MyActivity activity;        

    TaskAsynTask(MyActivity activity) {
        this.activity = activity;
    }

    @Override
    protected void onPreExecute() {
        dialog = ProgressDialog.show(activity, "title", "message");
        super.onPreExecute();
    }

    @Override
    protected Void doInBackground(Void... params) {
        //very long computation...
        return null;
    }

    @Override
    protected void onPostExecute(Void void) {
        dialog.cancel();
    }
}