背水一戰 Windows 10 (119) - 後臺任務: 後臺下載任務（任務分組，組完成後觸發後臺任務）
阿新 • • 發佈：2018-06-22
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[源碼下載]
作者：webabcd
介紹
背水一戰 Windows 10 之 後臺任務
- 後臺下載任務（任務分組，組完成後觸發後臺任務）
示例
演示後臺下載任務的分組，以及組任務全部完成後如何觸發後臺任務
/BackgroundTaskLib/BackgroundTaskTransfer.cs
/* * 後臺任務，用於演示指定的一組後臺下載任務全部完成後如何觸發此後臺任務 * * BackgroundTransferCompletionGroup - 分組對象（用於實現“組任務全部完成後觸發後臺任務”） * Enable() - 啟用“組任務全部完成後觸發後臺任務”的功能 * IsEnabled - 是否啟用了“組任務全部完成後觸發後臺任務”的功能（只讀） * Trigger - “組任務全部完成後觸發後臺任務”的觸發器 * * BackgroundDownloader - 後臺下載任務管理器 * BackgroundDownloader(BackgroundTransferCompletionGroup completionGroup) - 通過指定的 BackgroundTransferCompletionGroup 對象實例化 BackgroundDownloader 對象 * CompletionGroup - 獲取關聯的 BackgroundTransferCompletionGroup 對象 * * * 註：需要在 Package.appxmanifest 添加“後臺任務”聲明，支持的任務類型選擇“系統事件”，並指定 EntryPoint（後臺任務的類全名），類似如下： * <Extension Category="windows.backgroundTasks" EntryPoint="BackgroundTaskLib.BackgroundTaskTransfer"> * <BackgroundTasks> * <Task Type="systemEvent" /> * </BackgroundTasks> * </Extension>*/ using System; using System.Collections.Generic; using System.Threading.Tasks; using Windows.ApplicationModel.Background; using Windows.Data.Xml.Dom; using Windows.Networking.BackgroundTransfer; using Windows.UI.Notifications; namespace BackgroundTaskLib { public sealed class BackgroundTaskTransfer : IBackgroundTask {// 所註冊的後臺任務的名稱 public static string TaskName { get; set; } = "Transfer"; // 所註冊的後臺任務的 EntryPoint，即後臺任務的類全名 public static string TaskEntryPoint { get; set; } = "BackgroundTaskLib.BackgroundTaskTransfer"; // 實現 IBackgroundTask 接口，其只有一個方法，即 Run() public void Run(IBackgroundTaskInstance taskInstance) {// 獲取 BackgroundTransferCompletionGroupTriggerDetails 對象，如果不是 null 則說明是 BackgroundTransferCompletionGroup.Trigger 觸發的 BackgroundTransferCompletionGroupTriggerDetails details = taskInstance.TriggerDetails as BackgroundTransferCompletionGroupTriggerDetails; if (details == null) { return; } // 獲取下載任務列表 List<DownloadOperation> failedDownloads = new List<DownloadOperation>(); int successTotal = 0; foreach (DownloadOperation download in details.Downloads) { if (IsFailed(download)) { // 保存失敗的下載任務列表，稍後會重試 failedDownloads.Add(download); } else { successTotal++; } } if (failedDownloads.Count > 0) { // 重新下載失敗的任務 RetryDownloads(failedDownloads); } // 此後臺任務執行完畢，彈出指定的 toast 通知 ShowToast(successTotal, failedDownloads.Count); } // 判斷指定的下載任務是否失敗了 private bool IsFailed(DownloadOperation download) { BackgroundTransferStatus status = download.Progress.Status; if (status == BackgroundTransferStatus.Error || status == BackgroundTransferStatus.Canceled) { return true; } ResponseInformation response = download.GetResponseInformation(); if (response.StatusCode != 200) { return true; } return false; } // 重新下載指定的任務 private void RetryDownloads(IEnumerable<DownloadOperation> downloads) { // 註冊指定的後臺任務，並返回與此後臺任務相關聯的 BackgroundDownloader 對象 BackgroundDownloader downloader = BackgroundTaskTransfer.RegisterBackgroundTaskAndReturnBackgrounDownloader(); foreach (DownloadOperation download in downloads) { // 創建並啟動後臺任務 DownloadOperation downloadNew = downloader.CreateDownload(download.RequestedUri, download.ResultFile); Task<DownloadOperation> startTask = downloadNew.StartAsync().AsTask(); } // 啟用“組任務全部完成後觸發後臺任務”的功能 downloader.CompletionGroup.Enable(); } // 註冊指定的後臺任務，並返回與此後臺任務相關聯的 BackgroundDownloader 對象 // 後臺任務的註冊一般是在前臺代碼中寫的，但是由於本例還有一個後臺任務執行完成後重新下載失敗任務的功能，所以這部分代碼寫在後臺代碼中就很合理了 public static BackgroundDownloader RegisterBackgroundTaskAndReturnBackgrounDownloader() { // 根據指定 BackgroundTransferCompletionGroup 對象創建一個 BackgroundDownloader 對象 BackgroundTransferCompletionGroup completionGroup = new BackgroundTransferCompletionGroup(); BackgroundDownloader downloader = new BackgroundDownloader(completionGroup); // 註冊一個後臺任務，並指定觸發器為 BackgroundTransferCompletionGroup.Trigger BackgroundTaskBuilder builder = new BackgroundTaskBuilder(); builder.Name = BackgroundTaskTransfer.TaskName; builder.TaskEntryPoint = BackgroundTaskTransfer.TaskEntryPoint; builder.SetTrigger(completionGroup.Trigger); BackgroundTaskRegistration task = builder.Register(); return downloader; } // 後臺任務執行完成後彈出 toast 通知 private void ShowToast(int successTotal, int failureTotal) { string toastXml = $@" <toast activationType=‘foreground‘> <visual> <binding template=‘ToastGeneric‘> <text>toast - title</text> <text>下載任務成功數: {successTotal}</text> <text>下載任務失敗數: {failureTotal}</text> </binding> </visual> </toast>"; XmlDocument toastDoc = new XmlDocument(); toastDoc.LoadXml(toastXml); ToastNotificationManager.CreateToastNotifier().Show(new ToastNotification(toastDoc)); } } }
BackgroundTask/TransferModel.cs
/* * 擴展了 DownloadOperation 和 UploadOperation，用於 MVVM 綁定數據 */ 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/TransferBackground.xaml
<Page x:Class="Windows10.BackgroundTask.TransferBackground" 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="btnAddDownloadAndRegister" Content="新增一組（3 個）下載任務，並註冊指定的後臺任務，當這一組下載任務全部完成後觸發一個後臺任務。" Margin="5" Click="btnAddDownloadAndRegister_Click" /> <Button Name="btnRemoveDownloadAndUnregister" Content="取消下載任務並註銷指定的後臺任務" Margin="5" Click="btnRemoveDownloadAndUnregister_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/TransferBackground.xaml.cs
/* * 演示後臺下載任務的分組，以及組任務全部完成後如何觸發後臺任務 * * BackgroundTransferCompletionGroup - 分組對象（用於實現“組任務全部完成後觸發後臺任務”） * Enable() - 啟用“組任務全部完成後觸發後臺任務”的功能 * IsEnabled - 是否啟用了“組任務全部完成後觸發後臺任務”的功能（只讀） * Trigger - “組任務全部完成後觸發後臺任務”的觸發器 * * BackgroundDownloader - 後臺下載任務管理器 * BackgroundDownloader(BackgroundTransferCompletionGroup completionGroup) - 通過指定的 BackgroundTransferCompletionGroup 對象實例化 BackgroundDownloader 對象 * CompletionGroup - 獲取關聯的 BackgroundTransferCompletionGroup 對象 * * * 註：需要引用後臺任務項目，相關代碼參見 BackgroundTaskLib/BackgroundTaskTransfer.cs */ using BackgroundTaskLib; using System; using System.Collections.Generic; using System.Collections.ObjectModel; using System.Linq; using System.Threading; using System.Threading.Tasks; using Windows.ApplicationModel.Background; using Windows.Networking.BackgroundTransfer; using Windows.Storage; using Windows.UI.Core; using Windows.UI.Xaml; using Windows.UI.Xaml.Controls; using Windows.UI.Xaml.Navigation; using Windows.Web; namespace Windows10.BackgroundTask { public sealed partial class TransferBackground : Page { // 後臺任務是否已在系統中註冊 private bool _taskRegistered = false; // 下載任務的集合 private ObservableCollection<TransferModel> _transfers = new ObservableCollection<TransferModel>(); // 所有下載任務的關聯的 CancellationTokenSource 對象 private CancellationTokenSource _cancelToken = new CancellationTokenSource(); public TransferBackground() { this.InitializeComponent(); Init(); } private async void Init() { listView.ItemsSource = _transfers; // 加載存在的下載任務 await LoadDownloadAsync(); } // 加載存在的下載任務 private async Task LoadDownloadAsync() { IReadOnlyList<DownloadOperation> downloads = null; try { // 獲取存在的下載任務 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) { // 監視指定的後臺下載任務 tasks.Add(HandleDownloadAsync(download, false)); } await Task.WhenAll(tasks); } } protected override void OnNavigatedTo(NavigationEventArgs e) { // 遍歷所有已註冊的後臺任務 foreach (KeyValuePair<Guid, IBackgroundTaskRegistration> task in BackgroundTaskRegistration.AllTasks) { if (task.Value.Name == BackgroundTaskTransfer.TaskName) { _taskRegistered = true; break; } } UpdateUI(); } // 新增一組（3 個）下載任務，並註冊指定的後臺任務 private async void btnAddDownloadAndRegister_Click(object sender, RoutedEventArgs e) { // 註冊指定的後臺任務，並返回與此後臺任務相關聯的 BackgroundDownloader 對象 BackgroundDownloader downloader = BackgroundTaskTransfer.RegisterBackgroundTaskAndReturnBackgrounDownloader(); _taskRegistered = true; UpdateUI(); List<DownloadOperation> downloads = new List<DownloadOperation>(); for (int i = 0; i < 3; i++) { Uri uri = new Uri("http://files.cnblogs.com/webabcd/Windows10.rar"); StorageFile destinationFile; try { // 保存的目標地址（別忘了在 Package.appxmanifest 中配置好 <Capability Name="documentsLibrary" /> 和 .rar 類型文件的關聯） StorageFolder storageFolder = await KnownFolders.GetFolderForUserAsync(null, KnownFolderId.DocumentsLibrary); destinationFile = await storageFolder.CreateFileAsync("Windows10.rar", CreationCollisionOption.GenerateUniqueName); } catch (Exception ex) { WriteLine(ex.ToString()); return; } // 創建一個後臺下載任務 DownloadOperation download = downloader.CreateDownload(uri, destinationFile); downloads.Add(download); } // 啟用“組任務全部完成後觸發後臺任務”的功能 downloader.CompletionGroup.Enable(); WriteLine("用於完成後觸發後臺任務的一組下載任務創建完成了，相關的後臺任務也註冊了"); // 處理並監視組內的後臺下載任務 Task[] tasks = new Task[downloads.Count]; for (int i = 0; i < downloads.Count; i++) { tasks[i] = HandleDownloadAsync(downloads[i], true); } await Task.WhenAll(tasks); } /// <summary> /// 處理並監視組內的後臺下載任務 /// </summary> /// <param name="download">後臺下載任務</param> /// <param name="isNew">是否是新增的任務</param> private async Task HandleDownloadAsync(DownloadOperation download, bool isNew) { try { // 構造顯示用的相關數據 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()); // 當下載進度發生變化時的回調函數 Progress<DownloadOperation> progressCallback = new Progress<DownloadOperation>(DownloadProgress); if (isNew) await download.StartAsync().AsTask(_cancelToken.Token, progressCallback); // 啟動一個後臺下載任務 else await download.AttachAsync().AsTask(_cancelToken.Token, progressCallback); // 監視已存在的後臺下載任務 // 下載完成後獲取服務端的響應信息 ResponseInformation response = download.GetResponseInformation(); WriteLine("Completed: " + response.ActualUri + ", HttpStatusCode: " + response.StatusCode.ToString()); } catch (TaskCanceledException) // 調用 CancellationTokenSource.Cancel() 後會拋出此異常 { WriteLine("Canceled: " + download.Guid); } catch (Exception ex) { // 將異常轉換為 WebErrorStatus 枚舉，如果獲取到的是 WebErrorStatus.Unknown 則說明此次異常不是涉及 web 的異常 WebErrorStatus error = BackgroundTransferError.GetStatus(ex.HResult); WriteLine(ex.ToString()); } finally { _transfers.Remove(_transfers.First(p => p.DownloadOperation == download)); } } // 進度發生變化時，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"); } // 向 lblMsg 中追加一行文本 private void WriteLine(string message) { var ignore = lblMsg.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => { lblMsg.Text += message; lblMsg.Text += Environment.NewLine; scrollViewer.ChangeView(0, scrollViewer.ScrollableHeight, 1f); }); } // 取消下載任務並註銷指定的後臺任務 private void btnRemoveDownloadAndUnregister_Click(object sender, RoutedEventArgs e) { // 取消下載任務 _cancelToken.Cancel(); _cancelToken.Dispose(); _cancelToken = new CancellationTokenSource(); // 註銷指定的後臺任務 foreach (KeyValuePair<Guid, IBackgroundTaskRegistration> task in BackgroundTaskRegistration.AllTasks) { if (task.Value.Name == BackgroundTaskTransfer.TaskName) { // 從系統中註銷指定的後臺任務。唯一一個參數代表如果當前後臺任務正在運行中，是否需要將其取消 task.Value.Unregister(true); break; } } _taskRegistered = false; UpdateUI(); } private async void UpdateUI() { await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => { btnAddDownloadAndRegister.IsEnabled = !_taskRegistered; btnRemoveDownloadAndUnregister.IsEnabled = _taskRegistered; }); } } }
OK
[源碼下載]
背水一戰 Windows 10 (119) - 後臺任務: 後臺下載任務（任務分組，組完成後觸發後臺任務）