Android-填充列表视图适配器的asynctask

Question

Basically the flow is like the following: when a fragment is created (or when the user swipes to refresh the layout), an AsyncTask is executed. The ASyncTask retrieves the info from a URL and setup an adapter which is then assigned to a ListView.

This is the code of the Fragment:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                     Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.tasks_page, container, false);
    mSwipeRefreshLayout = (SwipeRefreshLayout)
    rootView.findViewById(R.id.list_container);
    mSwipeRefreshLayout.setOnRefreshListener(this);
    mSwipeRefreshLayout.setColorSchemeResources(android.R.color.holo_blue_bright,    
    android.R.color.holo_green_light, android.R.color.holo_red_light);

    lv = (ListView) rootView.findViewById(android.R.id.list);
    getTasks();

    return rootView;
}

private void getTasks() {
    new TasksRetriever(mSwipeRefreshLayout,tasksAdapter,lv).execute();
}

@Override
public void onRefresh() {
    mSwipeRefreshLayout.setRefreshing(true);
    new Handler().postDelayed(new Runnable() {
                @Override
                public void run() {
                    getTasks();
                }
            }, 1000);
}

The TaskRetriever constructor is:

public TasksRetriever(SwipeRefreshLayout srl, TasksAdapter ta, ListView lv) {
    adpt = ta;
    this.srl = srl;
    this.lv = lv;
}

and postExecute is:

@Override
protected void onPostExecute(List<TasksItem> result) {
    super.onPostExecute(result);
    dialog.dismiss();
    if (adpt == null) adpt = new TasksAdapter(result);
    else adpt.setItemList(result);
    lv.setAdapter(adpt);
    adpt.notifyDataSetChanged();
    srl.setRefreshing(false);
}

Not sure yet if it works but I was wondering if I'm on the right track because it doesn't look clean to me. On the other hand, I can't create the adapter and assign it to the ListView until I actually have data for it... Is this considering OK or am I doing it wrong?

Answer 1

I would set the list adapter up in the onCreate() method under your list view and make this a instance variable (not a local one) so that the Async task can access it as follows ie

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                     Bundle savedInstanceState) {

    lv = (ListView) rootView.findViewById(android.R.id.list);
    mAdpt = new TasksAdapter(null);
    lv.setAdapter(mAdpt);

}

And then in your onPostExecute()

@Override
protected void onPostExecute(List<TasksItem> result) {
    dialog.dismiss();  
    mAdpt.clear();
    for( TaskItem ti : result ) 
    {
      mAdpt.add( ti );
    }
    mAdpt.notifyDataSetChanged();
    srl.setRefreshing(false);
}

Also make sure you account for the null value being passed into your adapter in the getView() method.

Hope this helps.

Answer 2

you CAN create an empty adapter and fill it later - in AsyncTask

your onPostExecute() should look like:

@Override
protected void onPostExecute(List<TasksItem> result) {
    dialog.dismiss();
    if (adpt == null){
      adpt = new TasksAdapter(result);
      lv.setAdapter(adpt);
    }else{
      adpt.clear();
    }
    for( TaskItem ti : result ) adpt.add( ti );
    adpt.notifyDataSetChanged();
    srl.setRefreshing(false);
}