[問題]下載多個檔案使用ProgressDialog問題

[Dong0129 (阿東)]

各位版友好，

最近在寫透過ProgressDialog依序顯示多個URL下載檔案的APP時有個問題
一直不知道該怎麼解，程式碼及敘述如下...

將多個url存入一個array list中，依序將這些url丟入function中可透過Progress Dialo
g
讓使用者可以看到每個檔案的下載進度，每個檔案下載完後，Progress Dialog關閉，
等到下一個url被傳入downloadFile(url)時，再開啟一個Progress Dialog顯示進度條，
但目前只有第一筆url會正常顯示進度條，第二筆url的進度條一直停留在0%，但事實上
檔案有被下載到目的地中...請問是否哪裡寫錯了呢?

in Main:

for(String url:urls)
{
    downloadFile(url);
}

downloadFile() function:

private  void download(String data)
{
    app_name=data
             .substring(data.indexOf("0%2F"),data.indexOf("apk"))
             .replace("0%2F","")
             .replace(".",".apk");

    final DownloadTask downloadTask = new DownloadTask(MainActivity.this);
    downloadTask.execute(data);
    mProgressDialog.setOnCancelListener(new DialogInterface.OnCancelListener()
 {
            @Override
            public void onCancel(DialogInterface dialog) {
                downloadTask.cancel(true);
            }
        });
}

private class DownloadTask extends AsyncTask<String, Integer, String>
{
    private Context context;
    private PowerManager.WakeLock mWakeLock;

    public DownloadTask(Context context)
    {
        this.context = context;
    }

    @Override
    protected String doInBackground(String... sUrl)
    {
        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(sUrl[0]);
            Log.i("Eden","surl:"+sUrl[0]);
            app_name=sUrl[0]
                     .substring(sUrl[0].indexOf("0%2F"),sUrl[0].indexOf("apk")
)
                     .replace("0%2F","")
                     .replace(".",".apk");
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();
            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK)
            {
                return "Server returned HTTP "
                      + connection.getResponseCode()
                      + " "
                      + connection.getResponseMessage();
            }
            int fileLength = connection.getContentLength();
            // download the file
            input = connection.getInputStream();
            output = new FileOutputStream("/storage/emulated/0/Download/"
                                          +app_name);
            byte data[] = new byte[4096];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1)
            {
                if (isCancelled())
                {
                    input.close();
                    return null;
                }
                total += count;
                if (fileLength > 0)
                    publishProgress((int) (total * 100 / fileLength));
                output.write(data, 0, count);
            }
        } catch (Exception e) {
                return e.toString();
        } finally {
                try {
                    if (output != null)
                        output.close();
                    if (input != null)
                        input.close();
                } catch (IOException ignored) {
                }
                if (connection != null)
                    connection.disconnect();
            }
            return null;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            mProgressDialog = new ProgressDialog(MainActivity.this);
            mProgressDialog.setTitle("Downloading...");
            mProgressDialog.setMessage("Downloading "+app_name);
            mProgressDialog.setIndeterminate(false);
            mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            mProgressDialog.setCancelable(true);
            mProgressDialog.setMax(100);
            PowerManager pm = (PowerManager) context
                                     .getSystemService(Context.POWER_SERVICE);
            mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
                                       getClass().getName());
            mWakeLock.acquire();
            mProgressDialog.show();
        }
        @Override
        protected void onProgressUpdate(Integer... progress) {
            super.onProgressUpdate(progress);
            // if we get here, length is known, now set indeterminate to false
            mProgressDialog.setProgress(progress[0]);
        }
        @Override
        protected void onPostExecute(String result) {
            mWakeLock.release();
            mProgressDialog.dismiss();
            if (result != null)
                Toast.makeText(context,"Download error: "+result,
                               Toast.LENGTH_LONG).show();
            else
                Toast.makeText(context,"File downloaded",
                               Toast.LENGTH_SHORT).show();
        }
}

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推 andy2151: 異步執行你有了解運作原理嗎
→ andy2151: 看起來你在主程式的for一次就把所有下載同時進行
是的，程式運作是非同步所以第二個ProgressDialog彈出來後它就收不到download task
的
資料，因為第2個檔案已經下載完了...我想請問是否有方法能夠達成我要的效果呢?
※ 編輯: Dong0129 (36.227.181.38), 08/21/2018 23:19:33
推 andy2151: 你要在第一個異步執行完成後在進行第二個下載
推 andy2151: 建立一個變數downloadCount
→ andy2151: 記住目前下載到哪 在onPostExecute中 downloadCount++;
→ andy2151:  dowbliadFile(urls [downloadCount]);
已成功，原來一開始想的方向就錯了，謝謝！

→ zcbxvsdf: 只開一個thread跑所有download,用Handler 傳遞message
哈，這是另一種寫法，是抓download id去算檔案下載進度吧！

這兩種寫法的差異在哪呢？

推 t52101t: 把urls直接傳到asynctask裡面再用迴圈依次下載不好嗎
也是可行，一開始我想到的方向有點偏了，謝謝
※ 編輯: Dong0129 (114.137.240.236), 08/23/2018 09:35:02
推 baobomb: 建議用rxJava 會比較容易處理這種資料流的event