背水一战 Windows 10 (118) - 后台任务: 后台下载任务（任务分组，并行或串行执行，组完成后通知）
作者：webabcd
介绍
背水一战 Windows 10 之 后台任务
- 后台下载任务（任务分组，并行或串行执行，组完成后通知）
示例
演示后台下载任务的分组，以及如何设置组内任务是并行执行还是串行执行，以及组任务全部完成后如何 toast 或 tile 通知）
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/TransferGroup.xaml
<Page
x:Class="Windows10.BackgroundTask.TransferGroup"
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="新增一组（3 个）下载任务，可以指定其是并发还是串行，当这一组的所有任务都完成后弹出通知" Margin="5" Click="btnAddDownload_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/TransferGroup.xaml.cs
/*
* 演示后台下载任务的分组，以及如何设置组内任务是并行执行还是串行执行，以及组任务全部完成后如何 toast 或 tile 通知）
*
* BackgroundTransferGroup - 后台下载任务的分组对象
* static BackgroundTransferGroup CreateGroup(string name) - 创建指定分组标识的 BackgroundTransferGroup 对象
* Name - 分组标识（只读）
* TransferBehavior - 组内下载任务的执行方式，BackgroundTransferBehavior 枚举
* Parallel - 并行
* Serialized - 串行
*
* BackgroundDownloader - 后台下载任务管理器
* TransferGroup - 设置或获取分组对象（BackgroundTransferGroup 类型）
* static GetCurrentDownloadsForTransferGroupAsync(BackgroundTransferGroup group) - 获取指定组的所有下载任务
*
* DownloadOperation - 下载任务对象
* TransferGroup - 获取此下载任务的分组对象（BackgroundTransferGroup 类型）
*/ 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.UI.Notifications;
using Windows.Data.Xml.Dom; namespace Windows10.BackgroundTask
{
public sealed partial class TransferGroup : Page
{
// 用于后台任务的分组（通过组名标识后台任务）
private BackgroundTransferGroup _group = BackgroundTransferGroup.CreateGroup("my_group"); // 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 TransferGroup()
{
this.InitializeComponent(); Init();
} private async void Init()
{
// 指定组内任务并行执行
_group.TransferBehavior = BackgroundTransferBehavior.Parallel; listView.ItemsSource = _transfers; // 加载指定组的下载任务
await LoadDownloadAsync();
} // 加载指定组的下载任务
private async Task LoadDownloadAsync()
{
IReadOnlyList<DownloadOperation> downloads = null;
try
{
// 获取指定组的下载任务
downloads = await BackgroundDownloader.GetCurrentDownloadsForTransferGroupAsync(_group);
}
catch (Exception ex)
{
WriteLine(ex.ToString());
return;
} if (downloads.Count > )
{
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);
}
} // 新增一组（3 个）下载任务
private async void btnAddDownload_Click(object sender, RoutedEventArgs e)
{
BackgroundDownloader backgroundDownloader = new BackgroundDownloader();
// 指定分组
backgroundDownloader.TransferGroup = _group;
// 组任务全部成功后弹出指定的 toast 通知（类似的还有 SuccessTileNotification, FailureToastNotification, FailureTileNotification）
backgroundDownloader.SuccessToastNotification = GetToastNotification(_group.Name); List<DownloadOperation> downloads = new List<DownloadOperation>();
for (int i = ; i < ; i++)
{
Uri sourceUri = new Uri("http://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;
}
// 创建一个后台下载任务
DownloadOperation download = backgroundDownloader.CreateDownload(sourceUri, destinationFile); downloads.Add(download);
} // 处理并监视组内的后台下载任务
Task[] tasks = new Task[downloads.Count];
for (int i = ; i < downloads.Count; i++)
{
tasks[i] = HandleDownloadAsync(downloads[i], true);
} await Task.WhenAll(tasks); } /// <summary>
/// 处理并监视组内的后台下载任务
/// </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");
} // 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(, scrollViewer.ScrollableHeight, 1f);
} private ToastNotification GetToastNotification(string groupName)
{
string toastXml = $@"
<toast activationType='foreground'>
<visual>
<binding template='ToastGeneric'>
<text>toast - title</text>
<text>组 {groupName} 中的下载任务全部完成了</text>
</binding>
</visual>
</toast>"; XmlDocument toastDoc = new XmlDocument();
toastDoc.LoadXml(toastXml); return new ToastNotification(toastDoc);
}
}
}
OK
[源码下载]