Question

我的应用从互联网上下载了几张图片，并在一个进度条中显示整体下载的进度。问题是当使用BackgroundTransferService时，进度没有正确更新。

这就是我所拥有的。

从我的PhoneApplicationPage_Loaded我打电话下载我要下载的图片网址列表。

WebClient wc = new WebClient();
wc.DownloadStringCompleted += wc_DownloadStringCompleted;
wc.DownloadStringAsync(new Uri(MyDownloadList), null);

然后在wc_DownloadStringCompleted我在DownloadProgress中注册了自定义事件DownloadManagerClass，更新了用户界面pbDownloadProgress

中的进度条

然后我调用添加新BackgroundTransferRequest的代码并注册TransferStatusChanged和TransferProgressChanged（位于DownloadManagerClass中）。

void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
{    
    var up = e.Result;

        Dispatcher.BeginInvoke(() => txtDownloadProgressText.Text = "Downloading");

        downloadManager.DownloadProgress += (src, args) =>
        {
           Debug.WriteLine("Updating progress to " + args.Progress ` 100);
           Dispatcher.BeginInvoke(() =>
           {
               if (pbDownloadProgress.IsIndeterminate)
               {
                   pbDownloadProgress.IsIndeterminate = false;
                   pbDownloadProgress.Minimum = 0;
                   pbDownloadProgress.Maximum = 100;
               }
               pbDownloadProgress.Value = args.Progress * 100;
           });
        };

        BackgroundWorker bg = new BackgroundWorker();
        bg.DoWork += (s, ev) =>
        {
            downloadManager.DownloadImages(up);
        };
        bg.RunWorkerAsync();
    }
}

我的DownloadImages方法

internal void DownloadImages(String result)
{   
    List<String> URLs = ConvertStringToListUrls(result);

    var localFile = IsolatedStorageFile.GetUserStoreForApplication();
    if (!localFile.DirectoryExists(TRANSFERS_DIRECTORY))
    {
        localFile.CreateDirectory(TRANSFERS_DIRECTORY);
    }

    numberDownloadedItems = 0;
    totalDownloadingItems = URLs.Count;
    foreach (String item in URLs)
    {
        Debug.WriteLine("Adding Uri:" + uri);
        Uri transferUri = new Uri(Uri.EscapeUriString(item), UriKind.RelativeOrAbsolute);
        BackgroundTransferRequest transferRequest = new BackgroundTransferRequest(transferUri);
        transferRequest.Method = "GET";

        string downloadFile = transferFileName.Substring(transferFileName.LastIndexOf("/") + 1);
        Uri downloadUri = new Uri(TRANSFERS_DIRECTORY + "/" + downloadFile, UriKind.RelativeOrAbsolute);
        transferRequest.DownloadLocation = downloadUri;

        transferRequest.TransferStatusChanged += new EventHandler<BackgroundTransferEventArgs>(transfer_TransferStatusChanged);

        transferRequest.Tag = downloadFile;
        transferRequest.TransferPreferences = TransferPreferences.AllowCellularAndBattery;            

        BackgroundTransferService.Add(transferRequest);
        Debug.WriteLine("Adding transferID: " + transferRequest.RequestId);
    }
}

最后我的transfer_TransferStatusChanged方法，主要在一个文件完成时调用DownloadProgress事件。

void transfer_TransferProgressChanged(object sender, BackgroundTransferEventArgs e)
{
    if (transfer.TransferStatus == TransferStatus.Completed && (transfer.StatusCode == 200 || transfer.StatusCode == 206)) {
        if (RemoveTransferRequest(transfer.RequestId))
            if (DownloadProgress != null) DownloadProgress(this, new ProgressEventArgs(++numberDownloadedItems, totalDownloadingItems));                                
    }
}

每一步似乎都运行良好，但问题是在输出中我得到调试消息，指示应该更新的进度（如下所示），但进度条本身保持不变。

Removing transferID: {05ea9c10-025f-4e90-bc55-e9d36424b5f0}
10:37:27 AM:200: Updating progress to 14.2857142857143
Removing transferID: {e92f79fe-dc99-48b3-b0b1-76d3f5cedd51}
10:37:27 AM:651: Updating progress to 21.4285714285714
Removing transferID: {f61c8c9e-aa41-4e2a-8906-fca06961e69e}
10:37:28 AM:30: Updating progress to 28.5714285714286
Removing transferID: {46abc1df-37e6-432a-9b55-0adb3a8a2235}

我已经尝试删除调度程序使用，重新组织代码，但我似乎无法让它工作。

PS：我从代码中删除了一些异常以保持简单

BackgroundTransferService不会更新UI

0 个答案: