Android AsyncTask确保所有数据均已加载

Question

Hi I'm trying to create an Asynctask that runs two functions and when they are done loading it then fills the UI with the data. at the moment for somereason it only fills the UI with data from one of the Functions and its which ever of the functions finishes loading first.

For Example

i have two functions LoadNewsFeed() and LoadResultsFeed() at the moment loadResultsFeed() shows the data and not anything from loadNews() however if i comment out LoadResultsFeed() the data from loadNews fills The UI but not from loadResultsFeed

is there a way i could set it to if that one is finished loading, load the other than perform the FillData() function?

heres what i have so far

public class PostTask extends AsyncTask {

    @Override
    protected Boolean doInBackground(Void... params) {
        boolean result = false;

        loadNewsFeed();

        publishProgress("method1");
        loadResultsFeed();
        publishProgress("method2");
        return result;
    }


    protected void onProgressUpdate(String... progress) {
        StringBuilder str = new StringBuilder();
            for (int i = 1; i < progress.length; i++) {
                str.append(progress[i] + " ");

            }
    }

        @Override
    protected void onPostExecute(Boolean result) {
        super.onPostExecute(result);
        Log.v("BGThread", "begin fillin data");
         FillData();
    }
}

heres my FillData() Function

public void FillData(){ 


     if (ChosenMethod.equals("Team")) {




        arrayAdapter = new ArrayAdapter<String>(this, R.layout.single_item, newsList);

         String[] mStrings = (String[]) imageList.toArray(new String[imageList.size()]);
         String[] news = (String[]) newsList3.toArray(new String[newsList3.size()]);

         arrayAdapter3 = new LazyAdapter(this, mStrings, news);


            ListView list = getListView();
               list.setTextFilterEnabled(true);

               LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE );
                View header = inflater.inflate( R.layout.homeheader, list, false);
                View header2 = inflater.inflate( R.layout.homeheader2, list, false);
                View header3 = inflater.inflate( R.layout.homeheader3, list, false);


        //setListAdapter (arrayAdapter);

                 resultsView = LayoutInflater.from(getBaseContext()).inflate(R.layout.resultscell,
                         null);

               TextView homeTeam = (TextView) resultsView.findViewById(R.id.HomeTeam);
               homeTeam.setText(HomeTeam);

               TextView awayTeam = (TextView) resultsView.findViewById(R.id.AwayTeam);
               awayTeam.setText(AwayTeam);

               TextView homeScore = (TextView) resultsView.findViewById(R.id.HomeScore);
               homeScore.setText(HomeScore);

               TextView awayScore = (TextView) resultsView.findViewById(R.id.AwayScore);
               awayScore.setText(AwayScore);

               TextView attendance = (TextView) resultsView.findViewById(R.id.Attendence);
               attendance.setText("Att:" + Attendance);

               TextView division = (TextView) resultsView.findViewById(R.id.Division);
               division.setText(Division);

               Log.v("BGThread", "Filled results");

            adapter = new MergeAdapter();
            adapter.addView(header);
            adapter.addAdapter(arrayAdapter);
            adapter.addView(header2);
            adapter.addView(resultsView);
            adapter.addView(header3);
            adapter.addAdapter(arrayAdapter3);
            setListAdapter(adapter);

            Log.v("BGThread", "Filled Merge Adapter Team");

     } else {

         arrayAdapter = new ArrayAdapter<String>(this, R.layout.single_item, newsList);
            arrayAdapter2 = new ArrayAdapter<String>(this, R.layout.single_item, newsList2);
            //arrayAdapter3 = new ArrayAdapter(this, R.layout.complex_item, newsList3);

             String[] mStrings = (String[]) imageList.toArray(new String[imageList.size()]);
             String[] news = (String[]) newsList3.toArray(new String[newsList3.size()]);


             arrayAdapter3 = new LazyAdapter(this, mStrings, news);


                ListView list = getListView();
                   list.setTextFilterEnabled(true);

                   LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE );
                    View header3 = inflater.inflate( R.layout.homeheader3, list, false);


            //setListAdapter (arrayAdapter);


                adapter = new MergeAdapter();
                adapter.addView(header3);
                adapter.addAdapter(arrayAdapter3);
                setListAdapter(adapter);

                Log.v("BGThread", "Filled Merge Adapter League");
         } 
}

Answer 1

A quick and easy way is to add a boolean field to your class which is initially true:

private boolean bothFeedsLoaded = true;

Then toggle it's value in onPostExecute:

bothFeedsLoaded = !bothFieldsLoaded;

In your FillData method:

if (!bothFeedsLoaded){return;}

As bothFeedsLoaded is initially true, then the first callback to onPostExecute (after whichever feed loads first) will change it to false. Your fillData method will therefore return without doing anything. When the second feed finished loading, onPostEexcute will change it back to true and your fillData will do it's thing.

Alternatively (and perhaps a little easier to read in 6 months time) is to use an integer:

private int feedsLoaded = 0;

.....

feedsLoaded ++;

.....

if (feedsLoaded != 2) {return;}

There are better ways, eg creating separate classes for each loading task then synchronising both with a semaphore in their respective onPostExecute callbacks, but this should work.

Answer 2

If using AsyncTask is not crucial, i would suggest the use of Thread class along with Handler,

1. You can use join , the class which has those two methods, let it implement Runnable interface, then you can make an object of the class and pass it to the Thread constructor. Then use join on the thread, that means until and unless the thread dies it wont execute the below line, and just after the join, use the lines to place the data on the UI.

2. You can also you CountDownLatch from java.util.Concurrent package, which will wait for the specific work to be done, and then execute further.