我的侦听器中的Null指针异常

Question

I am making a call to my AsyncTask from my Fragment class, when i try to send the data back to my Fragment, i get a null pointer exception.

public interface AsyncListner { 
    public void onLoadComplete(List<DocumentResponse> documents);   
}

My Fragment class implements the interface.

public class FragmentClass extends SherlockFragment implements AsyncListner {@
    Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        new AsyncTask(Obj, getSherlockActivity()).setListener(this);
        new AsyncTask(Obj, getSherlockActivity()).execute();
    }

    @Override
    public void onLoadComplete(List < Response> data) {
        Log.d("Result", data.toString());
    }
}

I followed this answer. https://stackoverflow.com/a/13476196/98514

Answer 1

You have called new twice which created two different AsyncTasks:

new DocumentsAsyncTask(documentsObject, getSherlockActivity()).setListener(this);
new DocumentsAsyncTask(documentsObject, getSherlockActivity()).execute();

You should only create one:

DocumentsAsyncTask task = new DocumentsAsyncTask(documentsObject, getSherlockActivity());
task.setListener(this);
task.execute();

Notice the difference?
In your existing code you create:

• the first AsyncTask, where you set the listener but don't call execute() .
• the second AsyncTask, which has a null listener but you do call execute() .

In the new code, you have one AsyncTask which does both.

Answer 2

If a member variable for a class is null, it means you never initialized it to point to a non-null reference in a constructor.

All object reference types in Java are initialized to null until you point them to a reference that you've initialized with a call to new.

Where's your constructor?