Question

I’ve 6 different type of List results after completing AsyncTask. And the List results are should be returned to an Activity. For example: List<A>, List<B>, List<C>, List<D>, List<E> and finally List<F>.

This is my AsyncTask:

public class myAsync extends AsyncTask<String, String, List> {

    private List resultList;

    @Override
    protected List doInBackground(String... params) {
        //params[0] is url
        //params[1] is type
        callAPI api = new callAPI(params[0], params[1]);
        // According to type api decides type of List and generates
        return api.getJSON(); // returns a List which already parse JSON
    }

    @Override
    protected void onPostExecute(List result) {
        // Result is here now, may be 6 different List type.
        this.resultList = result 
    }

    // returns result
    public List getResultList() { return this.resultList; }
}

I’ll call AsyncTask like this:

myAsync task = new myAsync();
task.execute(params);
List myList = task.getResultList(); // type is uncertain
Log.d("Tag", Integer.toString(myList.size());

You know, I must point out the return type (Result) between <> tags. If I choose specific type for List, it does not work for other types.

Indeed, I already tried to return List<Object> and only List types. But doesn’t worked.

I don’t want to use 6 different Async. Is it possible to solve this with an only AsyncTask? I guess I need anonymous List or something similiar not sure. Can anyone explain this?

Answer 1

First, I should point out that the sequence in which you’re obtaining the list is not correct. Let me demonstrate:

// Initialize myAsync
myAsync task = new myAsync();

// This will do work for some period of time, this statement DOES NOT 'block'
// till myAsync completes, it will run it in the background
task.execute(params);

// This will return null because by the time you get here, task.execute most
// likely hasn't finished yet.
task.getResultList();

Edit: Now that you’ve included what you want to do with the list result, here’s how you would modify your onPostExecute method:

@Override
protected void onPostExecute(List result) {
  Log.d(TAG, "The returned list contains " +result.size()+ "elements");
  // Do anything else you need to with the returned list here
}

So to summarize, if you needed to do anything else with the returned lists (besides printing their size), for example compare, print items, etc, you need to do that in the onPostExecute method.