Question

I’m having a go at extending Activity to define a standard method I can callback to from an AsynchTask. Here’s a skeleton code.

public class R3Activity extends Activity{


    public void displayresult(String xmlresult){

    }//displayresult


}

Now any activities I create by extending R3Activity can implement a displayresult method.

I then use this as follows…..

    public class MainActivity extends R3Activity{


    private void somemethod(){
           DatabaseAccess dba = new DatabaseAccess();
           dba.setActivity(this); // Pass a ref to the activity into the class with the Asynch task
           dba.execute(new URL(database_url));

    }

    }

}

The DatabaseAccess class is supposed to be a generic class that goes off and fetches data using an AsnchTask. My problem is handling the callback in a generic way.

public class DatabaseAccess extends AsyncTask<URL, String, String> {
        private R3Activity m_activity;

    public void setActivity(R3Activity activity) {
        m_activity = activity;
    }

    @Override
    protected String doInBackground(URL... params) {
           //Connect to database etc
           String strdata = "blah";

        }

    protected void onPostExecute(String result) {
        if ((strdata != null) && (m_activity != null)) {

            m_activity.displayresult(strdata);

        }
    }

}

Now m_activity.displayresult works because this method is available in every instance of an R3Activity.

How do I get displayresult() to trigger an Event handler that I can implement in every Activity.

Something like….

public class MainActivity extends R3Activity implements  DatabaseResultListener {


public void DbCallback(){
//This gets triggerred by the displayresult callback
}

}

Answer 1

I think you should use interface for callback.and you can do it easily.

interface AsyncTaskListener{
     public void onTaskComplete(T result)
}

Then implements it

public class MainActivity extends Activity implements AsyncTaskListener

And in AsycTask,onPostExecute method call listener method like,

 objAsyncTaskListener.onTaskComplete(T result);

• See here