android - AsyncTask 文件下载时 ListView 中的进度条

Question

我有一个奇怪的问题，每当我在网络浏览器上找到一个 MP3 文件时，我都会启动一个新的异步任务，并在每个异步任务的 ListView 中启动一个进度条。所以下载的数量可以超过 1 并且是同时的。但是现在，每当启动 Asynctask 时，ProgressBar 对所有 AsyncTask 的移动都相同，并且对于不同的 AsyncTask 没有不同，请指导我......

    public class CopyOfDownloadsListActivity extends ListActivity {
    /** Called when the activity is first created. */

//  static ArrayList<String> pthreads = new ArrayList<String>();
ImageView bt;
ProgressBar pb;
ListView allList;
TextView tv;
String fileName;
String mp3URL;
    URL url2;
    int filecount  = 0;

private class DownloadFile extends AsyncTask<String, Integer, Void>{
    MyCustomAdapter adapter;

    int count = 0;
    ProgressDialog dialog;
    ProgressBar progressBar;
    int myProgress;

   @Override        
    protected Void doInBackground(String... u) {        
        try {                   
            URL ul = new URL(u[0]);
            Log.i("UI",ul.toString());
       //   int len = CopyOfMusicDownloader.mp3urls.size();
       //   URL url2 = new URL(CopyOfMusicDownloader.mp3urls.get(len-1));
            HttpURLConnection c = (HttpURLConnection) ul.openConnection();
            c.setRequestMethod("GET");
            c.setDoOutput(true);
            c.connect();

            int lengthOfFile = c.getContentLength();

            String PATH = Environment.getExternalStorageDirectory()
                    + "/download/";
            Log.v("", "PATH: " + PATH);
            File file = new File(PATH);
            file.mkdirs();

            fileName = "Track";
            filecount++;

            fileName =  fileName + Integer.toString(filecount) + ".mp3";


            File outputFile = new File(file, fileName);
            FileOutputStream fos = new FileOutputStream(outputFile);
            InputStream is = c.getInputStream();

            byte[] buffer = new byte[1024];
            int len1 = 0;      
            while ((len1 = is.read(buffer)) != -1) {
                myProgress = (int)((len1/lengthOfFile)*100);
                myProgress = myProgress + myProgress;
                Log.i("lengthOfFile", Integer.toString(lengthOfFile));
                Log.i("My Progress", Integer.toString(myProgress));
                publishProgress(myProgress);
                fos.write(buffer, 0, len1);
            }
            fos.close();
            is.close();

            }catch (IOException e) {
                   e.printStackTrace();
            }
        return null;
    }

    protected void onPostExecute() {
    }

    @Override
    protected void onPreExecute() {         
          adapter = new MyCustomAdapter(CopyOfDownloadsListActivity.this, R.layout.row, CopyOfMusicDownloader.mp3urls);
          setListAdapter(adapter);
    }



    @Override
    protected void onProgressUpdate(Integer... values) {
         Log.i("Value", values[0].toString());
         count++;
         adapter.notifyDataSetChanged();
    }


    public class MyCustomAdapter extends ArrayAdapter<String> {     
        public MyCustomAdapter(Context context, int textViewResourceId, ArrayList<String> pthreads) {
        super(context, textViewResourceId, pthreads);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
                LayoutInflater inflater = getLayoutInflater();
                View row = inflater.inflate(R.layout.row, parent, false);
                bt =(ImageView)row.findViewById(R.id.cancel_btn);
                tv =(TextView)row.findViewById(R.id.filetext);
                pb = (ProgressBar)row.findViewById(R.id.progressbar_Horizontal);
                pb.setProgress(count);  
                return row;
            }
        }       
 }  

这是 AsyncTask 的开始，它的 onCreate new DownloadFile().execute(url2.toString());

Answer 1

此外，请阅读此处关于 execute() 的注释:

http://developer.android.com/reference/android/os/AsyncTask.html#execute%28Params...%29

在 Honeycomb 之后，将只有一个线程运行所有 ASyncTasks，因此您可能无法同时运行多个线程。在第一个之后，其余的将排队并且在第一个完成之前根本不会执行。您可能需要在线程中执行每个下载并使用单个 ASyncTask 来监视所有下载。 (您也可以从线程进行监控，但您需要采取额外的步骤来安全地将更新发布到 UI 线程上的 UI)。