Android：一个带有两个AsyncTask的ProgressBar

Question

i have two AsyncTasks (subclass of MainActivity ) which download some data simaultaniously. they are called by

new LoadData(url).executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);

I want them both to update a ProgressBar but I cant think of a way to setProgress from two simultaneous threads so that each thread contributes 50% of the progress.

public class MainActivity extends Activity {
    private static double staticvariable = 0;
    private ProgressBar progbar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        progbar = (ProgressBar) findViewById(R.id.progressBar1);

        new LoadData("http://stackoverflow.com")
                .executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
        new LoadData("http://stackoverflow.com")
                .executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
    }

    private class LoadData extends AsyncTask<String, Void, String> {
        private String weburl;

        public LoadData(String url) {
            this.weburl = url;
            System.out.println("Starting Download");
        }

        protected String doInBackground(String... params) {
            System.out.println("point 1");
            URLConnection conn = null;
            URL url = null;
            try {
                url = new URL(weburl);
                conn = url.openConnection();
                conn.connect();
                InputStream in = null;
                in = new BufferedInputStream(url.openStream());
                int fileSize = conn.getContentLength();
                double taskProgress;
                int count;
                byte buffer[] = new byte[1024];
                while ((count = in.read(buffer)) != -1) {
                    taskProgress = 50 * ((double) count) / ((double) fileSize);
                    staticvariable += taskProgress;
                    progbar.setProgress((int) staticvariable);
                }
                in.close();
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }



            System.out.println("finished at " + (int) staticvariable + "%");
            return null;

        }
    }
}

I think the solution lies with using a static variable incrementing itself by count/fileSize as shown above but i get some strange results. At the end of each download i print the percent completion to the console i get:

finished at 916%

and

finished at 926%

I dont have a clue where these numbers are from. Any ideas?

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Edit Running only one AsyncTask outputs:

finished at 447%

Answer 1

It is simple (no code included, just algorithm):

1. Start by setting the maximum of your progress to 0.
2. When any of your asynctasks get their own max value, increment the maximum of the progress by this value.
3. Now as each of the asynctasks finish some of their work, increment the progress current value by that amount.
4. When all of your asynctasks are done, the amount of work done will sum up to the sum of each asynctask's maximum value and you will get a 100% progress.

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As a side note, for this to be perfectly perfect, you probably need to set the maximum progress to the sum of each individual maximums before starting the actual work. However, this is a side note and can be discarded.