介绍
重新想象 Windows 8 Store Apps 之 后台任务
后台下载任务
后台上传任务
示例
扩展了 DownloadOperation 和 UploadOperation，以便下载进度或上传进度可通知
BackgroundTask/TransferModel.cs
/*
* 扩展了 DownloadOperation 和 UploadOperation，以便下载进度或上传进度可通知
*/
using System;
using System.ComponentModel;
using Windows.Networking.BackgroundTransfer;
namespace XamlDemo.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));
}
}
}
}
1、演示后台下载任务的应用
BackgroundTask/TransferDownload.xaml
<Page
x:Class="XamlDemo.BackgroundTask.TransferDownload"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:XamlDemo.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="120 0 0 0">
<ScrollViewer Height="100">
<TextBlock Name="lblMsg" FontSize="14.667" TextWrapping="Wrap" />
</ScrollViewer>
<Button Name="btnAddDownload" Content="新增一个下载任务" Margin="0 10 0 0" Click="btnAddDownload_Click" />
<Button Name="btnPause" Content="暂停所有下载任务" Margin="0 10 0 0" Click="btnPause_Click" />
<Button Name="btnResume" Content="继续所有下载任务" Margin="0 10 0 0" Click="btnResume_Click" />
<Button Name="btnCancel" Content="取消所有下载任务" Margin="0 10 0 0" Click="btnCancel_Click" />
<ListView Name="listView" Padding="0 10 0 0" Height="300">
<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
/*
* 演示后台下载任务的应用
*
* BackgroundDownloader - 后台下载任务管理器
* CostPolicy - 下载的成本策略，BackgroundTransferCostPolicy 枚举
* Default - 不允许在高成本（比如 2G 3G）网络上传输
* UnrestrictedOnly - 允许在高成本（比如 2G 3G）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
* SetRequestHeader(string headerName, string headerValue) - 设置 http 请求头
* CreateDownload(Uri uri, IStorageFile resultFile) - 创建一个下载任务，返回 DownloadOperation 对象
* Group - 用于分组下载任务
* static GetCurrentDownloadsAsync(string group) - 获取指定组下的所有下载任务
* static GetCurrentDownloadsAsync() - 获取未与组关联的所有下载任务
*
* DownloadOperation - 下载任务对象
* CostPolicy - 下载的成本策略，BackgroundTransferCostPolicy 枚举
* Group - 获取此下载任务的所属组
* Guid - 获取此下载任务的标识
* RequestedUri - 下载的源 URI
* ResultFile - 下载的目标文件
* 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() - 暂停此任务
* Resume() - 继续此任务
* 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
*
* 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;
namespace XamlDemo.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;
// 获取全部下载任务
await LoadDownloadAsync();
}
// 加载全部下载任务
private async Task LoadDownloadAsync()
{
IReadOnlyList<DownloadOperation> downloads = null;
try
{
// 获取所有后台下载任务
downloads = await BackgroundDownloader.GetCurrentDownloadsAsync();
}
catch (Exception ex)
{
lblMsg.Text += ex.ToString();
lblMsg.Text += Environment.NewLine;
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)
{
// 下载地址（注意需要在 Package.appxmanifest 中增加对 .rar 类型文件的关联）
// 查看本栏目更多精彩内容：http://www.bianceng.cnhttp://www.bianceng.cn/Programming/net/
Uri sourceUri = new Uri("http://files.cnblogs.com/webabcd/Windows8.rar", UriKind.Absolute);
StorageFile destinationFile;
try
{
// 保存的目标地址
destinationFile = await KnownFolders.DocumentsLibrary.CreateFileAsync("Windows8.rar", CreationCollisionOption.GenerateUniqueName);
}
catch (Exception ex)
{
lblMsg.Text += ex.ToString();
lblMsg.Text += Environment.NewLine;
return;
}
// 创建一个后台下载任务
BackgroundDownloader backgroundDownloader = new BackgroundDownloader();
DownloadOperation download = backgroundDownloader.CreateDownload(sourceUri, destinationFile);
// 监视指定的后台下载任务
await HandleDownloadAsync(download, true);
}
/// <summary>
/// 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
{
// 将 DownloadOperation 附加到 TransferModel，以便下载进度可通知
TransferModel transfer = new TransferModel();
transfer.DownloadOperation = download;
transfer.Source = download.RequestedUri.ToString();
transfer.Destination = download.ResultFile.Path;
transfer.Progress = "0 / 0";
_transfers.Add(transfer);
lblMsg.Text += "Task Count: " + _transfers.Count.ToString();
lblMsg.Text += Environment.NewLine;
// 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); // 新增一个后台下载任务
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();
lblMsg.Text += "Completed: " + response.ActualUri + "-" + response.StatusCode.ToString();
lblMsg.Text += Environment.NewLine;
}
catch (TaskCanceledException) // 调用 CancellationTokenSource.Cancel() 后会抛出此异常
{
lblMsg.Text += "Canceled: " + download.Guid;
lblMsg.Text += Environment.NewLine;
}
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);
lblMsg.Text += ex.ToString();
lblMsg.Text += Environment.NewLine;
}
finally
{
_transfers.Remove(_transfers.First(p => p.DownloadOperation == download));
}
}
// 进度发生变化时，更新 TransferModel 的 Progress，以便通知
private void DownloadProgress(DownloadOperation download)
{
TransferModel transfer = _transfers.First(p => p.DownloadOperation == download);
transfer.Progress = 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)
{
lblMsg.Text += "All Paused";
lblMsg.Text += Environment.NewLine;
foreach (TransferModel transfer in _transfers)
{
if (transfer.DownloadOperation.Progress.Status == BackgroundTransferStatus.Running)
{
transfer.DownloadOperation.Pause();
}
}
}
// 继续全部后台下载任务
private void btnResume_Click(object sender, RoutedEventArgs e)
{
lblMsg.Text += "All Resumed";
lblMsg.Text += Environment.NewLine;
foreach (TransferModel transfer in _transfers)
{
if (transfer.DownloadOperation.Progress.Status == BackgroundTransferStatus.PausedByApplication)
{
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();
}
}
}
2、演示后台上传任务的应用
BackgroundTask/TransferUpload.xaml
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时间： 2024-12-31 19:44:26