背水一战 Windows 10 (117) - 后台任务: 后台下载任务
背水一战 Windows 10 (117) - 后台任务: 后台下载任务
作者：webabcd
介绍
背水一战 Windows 10 之 后台任务
- 后台下载任务
示例
演示 uwp 的后台下载任务
BackgroundTask/TransferModel.cs
/* * 扩展了 DownloadOperation 和 UploadOperation，用于 MVVM 绑定数据 */ using System; using System.ComponentModel; using Windows.Networking.BackgroundTransfer; namespace Windows10.BackgroundTask { public class TransferModel : INotifyPropertyChanged { public DownloadOperation DownloadOperation { get; set; } public UploadOperation UploadOperation { get; set; } public string Source { get; set; } public string Destination { get; set; } private string _progress; public string Progress { get { return _progress; } set { _progress = value; RaisePropertyChanged("Progress"); } } public event PropertyChangedEventHandler PropertyChanged; protected void RaisePropertyChanged(string name) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(name)); } } } }
BackgroundTask/TransferDownload.xaml
<Page x:Class="Windows10.BackgroundTask.TransferDownload" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="using:Windows10.BackgroundTask" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d"> <Grid Background="Transparent"> <StackPanel Margin="10 0 10 10"> <ScrollViewer Name="scrollViewer" Height="100" Margin="5"> <TextBlock Name="lblMsg" TextWrapping="Wrap" /> </ScrollViewer> <Button Name="btnAddDownload" Content="新增一个下载任务" Margin="5" Click="btnAddDownload_Click" /> <Button Name="btnPause" Content="暂停所有下载任务" Margin="5" Click="btnPause_Click" /> <Button Name="btnResume" Content="继续所有下载任务" Margin="5" Click="btnResume_Click" /> <Button Name="btnCancel" Content="取消所有下载任务" Margin="5" Click="btnCancel_Click" /> <ListView Name="listView" Height="286" Padding="5"> <ListView.ItemTemplate> <DataTemplate> <StackPanel Margin="0 5" Background="Blue"> <TextBlock Text="{Binding Source}" Margin="5" /> <TextBlock Text="{Binding Destination}" Margin="5" /> <TextBlock Text="{Binding Progress}" Margin="5" /> </StackPanel> </DataTemplate> </ListView.ItemTemplate> </ListView> </StackPanel> </Grid> </Page>
BackgroundTask/TransferDownload.xaml.cs
/* * 演示 uwp 的后台下载任务 * * BackgroundDownloader - 后台下载任务管理器 * CreateDownload(Uri uri, IStorageFile resultFile) - 创建一个下载任务，返回 DownloadOperation 对象 * SetRequestHeader(string headerName, string headerValue) - 设置 http 请求头 * Method - 用于下载的 http method（默认 get） * static GetCurrentDownloadsAsync() - 获取当前 app 的未与组关联的所有下载任务 * CostPolicy - 下载的成本策略，BackgroundTransferCostPolicy 枚举 * Default - 允许在高成本（比如 4G）网络上传输（默认值） * UnrestrictedOnly - 不允许在高成本（比如 4G）网络上传输 * Always - 无论如何均可传输，即使在漫游时 * ServerCredential - 与服务端通信时的凭据 * ProxyCredential - 使用代理时的身份凭据 * SuccessToastNotification, SuccessTileNotification, FailureToastNotification, FailureTileNotification - 下载任务成功或失败后的 toast 或 tile 通知 * * DownloadOperation - 下载任务对象 * Guid - 获取此下载任务的标识 * CostPolicy - 下载的成本策略，BackgroundTransferCostPolicy 枚举 * RequestedUri - 下载的源 URI * ResultFile - 下载的目标文件 * Method - 获取用于下载的 http method（get, post 之类的） * GetResponseInformation() - 下载完成后获取到的服务端响应信息，返回 ResponseInformation 对象 * ActualUri - 下载源的真实 URI * Headers - 服务端响应的 HTTP 头 * StatusCode - 服务端响应的状态码 * Pause() - 暂停此下载任务 * Resume() - 继续此下载任务 * StartAsync() - 新增一个下载任务，返回 IAsyncOperationWithProgress<DownloadOperation, DownloadOperation> 对象 * AttachAsync() - 监视已存在的下载任务，返回 IAsyncOperationWithProgress<DownloadOperation, DownloadOperation> 对象 * Progress - 获取下载进度，返回 BackgroundDownloadProgress 对象 * Priority - 下载的优先级，BackgroundTransferPriority 枚举 * Default 或 High * * BackgroundDownloadProgress - 后台下载任务的下载进度对象 * BytesReceived - 已下载的字节数 * TotalBytesToReceive - 总共需要下载的字节数，未知则为 0 * Status - 下载状态，BackgroundTransferStatus 枚举 * Idle, Running, PausedByApplication, PausedCostedNetwork, PausedNoNetwork, Completed, Canceled, Error * HasResponseChanged - 服务端响应了则为 true * HasRestarted - 当下载连接断掉后，系统会通过 http range 头向服务端请求断点续传，如果服务端不支持断点续传则需要重新下载，此种情况则为 true */ using System; using System.Collections.Generic; using System.Collections.ObjectModel; using System.Threading; using System.Threading.Tasks; using System.Linq; using Windows.Networking.BackgroundTransfer; using Windows.Storage; using Windows.UI.Xaml; using Windows.UI.Xaml.Controls; using Windows.Web; using Windows.Data.Xml.Dom; using Windows.UI.Notifications; namespace Windows10.BackgroundTask { public sealed partial class TransferDownload : Page { // 下载任务的集合 private ObservableCollection<TransferModel> _transfers = new ObservableCollection<TransferModel>(); // 所有下载任务的关联的 CancellationTokenSource 对象 private CancellationTokenSource _cancelToken = new CancellationTokenSource(); public TransferDownload() { this.InitializeComponent(); Init(); } private async void Init() { listView.ItemsSource = _transfers; // 加载存在的下载任务 await LoadDownloadAsync(); } // 加载存在的下载任务 private async Task LoadDownloadAsync() { IReadOnlyList<DownloadOperation> downloads = null; try { // 获取存在的下载任务 downloads = await BackgroundDownloader.GetCurrentDownloadsAsync(); } catch (Exception ex) { WriteLine(ex.ToString()); return; } if (downloads.Count > 0) { List<Task> tasks = new List<Task>(); foreach (DownloadOperation download in downloads) { // 监视指定的后台下载任务 tasks.Add(HandleDownloadAsync(download, false)); } await Task.WhenAll(tasks); } } // 新增一个下载任务 private async void btnAddDownload_Click(object sender, RoutedEventArgs e) { Uri sourceUri = new Uri("https://files.cnblogs.com/webabcd/Windows10.rar", UriKind.Absolute); StorageFile destinationFile; try { // 保存的目标地址（别忘了在 Package.appxmanifest 中配置好 <Capability Name="documentsLibrary" /> 和 .rar 类型文件的关联） StorageFolder storageFolder = await KnownFolders.GetFolderForUserAsync(null, KnownFolderId.DocumentsLibrary); destinationFile = await storageFolder.CreateFileAsync("Windows10.rar", CreationCollisionOption.GenerateUniqueName); } catch (Exception ex) { WriteLine(ex.ToString()); return; } BackgroundDownloader backgroundDownloader = new BackgroundDownloader(); // 任务成功后弹出指定的 toast 通知（类似的还有 SuccessTileNotification, FailureToastNotification, FailureTileNotification） backgroundDownloader.SuccessToastNotification = GetToastNotification(sourceUri); // 创建一个后台下载任务 DownloadOperation download = backgroundDownloader.CreateDownload(sourceUri, destinationFile); // 处理并监视指定的后台下载任务 await HandleDownloadAsync(download, true); } /// <summary> /// 处理并监视指定的后台下载任务 /// </summary> /// <param name="download">后台下载任务</param> /// <param name="isNew">是否是新增的任务</param> private async Task HandleDownloadAsync(DownloadOperation download, bool isNew) { try { // 构造显示用的相关数据 TransferModel transfer = new TransferModel(); transfer.DownloadOperation = download; transfer.Source = download.RequestedUri.ToString(); transfer.Destination = download.ResultFile.Path; transfer.Progress = download.Progress.Status.ToString() + ": 0 / 0"; _transfers.Add(transfer); WriteLine("Task Count: " + _transfers.Count.ToString()); // 当下载进度发生变化时的回调函数 Progress<DownloadOperation> progressCallback = new Progress<DownloadOperation>(DownloadProgress); if (isNew) await download.StartAsync().AsTask(_cancelToken.Token, progressCallback); // 启动一个后台下载任务 else await download.AttachAsync().AsTask(_cancelToken.Token, progressCallback); // 监视已存在的后台下载任务 // 下载完成后获取服务端的响应信息 ResponseInformation response = download.GetResponseInformation(); WriteLine("Completed: " + response.ActualUri + ", HttpStatusCode: " + response.StatusCode.ToString()); } catch (TaskCanceledException) // 调用 CancellationTokenSource.Cancel() 后会抛出此异常 { WriteLine("Canceled: " + download.Guid); } catch (Exception ex) { // 将异常转换为 WebErrorStatus 枚举，如果获取到的是 WebErrorStatus.Unknown 则说明此次异常不是涉及 web 的异常 WebErrorStatus error = BackgroundTransferError.GetStatus(ex.HResult); WriteLine(ex.ToString()); } finally { _transfers.Remove(_transfers.First(p => p.DownloadOperation == download)); } } // 进度发生变化时，更新 TransferModel 的 Progress private void DownloadProgress(DownloadOperation download) { TransferModel transfer = _transfers.First(p => p.DownloadOperation == download); transfer.Progress = download.Progress.Status.ToString() + ": " + download.Progress.BytesReceived.ToString("#,0") + " / " + download.Progress.TotalBytesToReceive.ToString("#,0"); } // 暂停全部后台下载任务 private void btnPause_Click(object sender, RoutedEventArgs e) { WriteLine("All Paused"); foreach (TransferModel transfer in _transfers) { transfer.DownloadOperation.Pause(); } } // 继续全部后台下载任务 private void btnResume_Click(object sender, RoutedEventArgs e) { WriteLine("All Resumed"); foreach (TransferModel transfer in _transfers) { transfer.DownloadOperation.Resume(); } } // 取消全部后台下载任务 private void btnCancel_Click(object sender, RoutedEventArgs e) { _cancelToken.Cancel(); _cancelToken.Dispose(); _cancelToken = new CancellationTokenSource(); } // 向 lblMsg 中追加一行文本 private void WriteLine(string message) { lblMsg.Text += message; lblMsg.Text += Environment.NewLine; scrollViewer.ChangeView(0, scrollViewer.ScrollableHeight, 1f); } // 构造指定的 toast 通知 private ToastNotification GetToastNotification(Uri sourceUri) { string toastXml = $@" <toast activationType='foreground'> <visual> <binding template='ToastGeneric'> <text>toast - title</text> <text>下载任务成功完成</text> <text>{sourceUri}</text> </binding> </visual> </toast>"; XmlDocument toastDoc = new XmlDocument(); toastDoc.LoadXml(toastXml); return new ToastNotification(toastDoc); } } }
OK
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