只能加载片段视图一次

Question

I've got the following. I have an navigation drawer. When I click on one item the main content frame gets replaced with another fragment dependent on what the user clicks on. The fragment then starts an asynctask to create the view. I do this so the app doesn't get stuck and the user can actually see that something is getting done.

The problem I'm encountering now is that, every time I click on the item the fragment gets loaded again. I know that this is because I'm calling my AsyncTask in the onCreate method of the fragment, but is there a work around on how to NOT load the whole thing again when it has been already loaded once?

Long story short:

I have a fragment that gets filled with data. I don't want the user to think that the app is stuck so I added a progress bar and an async task so the user can see that something's getting done.

Problem the app loads everything again when I click on one item Solution I want that when the fragment is loaded once it gets saved and not called again.

This is here my code. I minified it so you don't need to read too much. Just used the fewest lines possible

MAINFRAGMENT

@Override
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        new MainAsyncTask().execute();
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState){

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        StrictMode.setThreadPolicy(policy);
        View rootView = inflater.inflate(R.layout.main_fragment, container, false);
        rl = (RelativeLayout) rootView.findViewById(R.id.mainRelativeLayout);
        sv = (ScrollView) rootView.findViewById(R.id.mainScrollView);
        ll = (LinearLayout) rootView.findViewById(R.id.mainListView);
        progressBar = (ProgressBar) rootView.findViewById(R.id.progressBar1);
        return rootView;
    }

ASYNCTASK

private class MainAsyncTask extends AsyncTask<Void, Void, Void> {

        TextView[] source;
@Override
        protected void onPreExecute() {
//          super.onPreExecute();
            progress = 0;
        }

        @Override
        protected Void doInBackground(Void... params) {
            source      = new TextView[todayHashMapSize];
for (int i = 0; i < todayHashMapSize; i++) {

                source[i]       = new TextView(getActivity());
}
return null
}

protected void publishProgress(int value) {
               progressBar.setProgress(value);
        }

        @Override
        protected void onPostExecute(Void result){
            for (int i = 0; i < todayHashMapSize; i++) {
                ll.addView(source[i]);


            }
            ll.removeView(progressBar);

        }

So basically is there an option to check whether an layout already has been populated and if so how do I do that, where do I put that code?

My approach was to check whether ll has childs with

if(ll.getChildCount() == 0){
        new MainAsyncTask().execute();
    }

but that just gives me an nullPointerException at the exact same line

Answer 1

Use a headless fragment with a call to

setRetainInstance(true);

to prevent it being destroyed.

See these links for more info: http://www.vogella.com/articles/AndroidBackgroundProcessing/article.html#fragmentsandbackgroundprocessing

http://creeder.com/?&page=AsyncTask