Windows phone 8 学习笔记(6) 多任务

Windows phone 8 是一个单任务操作系统，任何时候都只有一个应用处于活跃状态，这里的多任务是指对后台任务的支持。本节我们先讲讲应用程序的运行状态，然后看看支持的后台任务，包括：后台代理、后台音频、后台文件传输、后台辅助线程等。

快速导航：
    一、应用的状态
    二、后台代理
    三、后台音频
    四、后台文件传输
    五、后台辅助线程

一、应用的状态

1）应用的运行状态

我们通过图解来分析应用的运行状态，启动并置于前台界面的应用是唯一处于运行状态的，其他的操作，比如win键，后退导出应用，打开选择器和启动器时都会让当前运行的应用进入休眠状态，如果系统内存不足，处于休眠状态的应用可能会被系统逻辑删除。下面的图示演示了这个过程。

2）如何恢复状态

当应用处于休眠状态时，它的状态信息仍然保留在内存中，用户下次切换进去后不会有任何变化。但是当应用被逻辑删除后，这些状态信息就会丢失，比如表单填写的内容都会消失，为了避免这种情况，我们需要手动保留状态信息。
    首先，我们在mainpage定义一些页面表单控件：

[XAML]
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<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
    <TextBox Text="{Binding TextBox1Text, Mode=TwoWay}" Height="72"
         HorizontalAlignment="Left" Margin="20,20,0,0" Name="textBox1"
         VerticalAlignment="Top" Width="440" />
                    <CheckBox IsChecked="{Binding CheckBox1IsChecked, Mode=TwoWay}"
         Content="CheckBox" Height="71" Name="checkBox1" Margin="20,100,0,0"
          VerticalAlignment="Top"/>
                    <Slider Value="{Binding Slider1Value, Mode=TwoWay}" Height="84" Name="slider1"
         Width="440" Margin="20,180,0,0"  VerticalAlignment="Top"/>
                    <RadioButton IsChecked="{Binding RadioButton1IsChecked, Mode=TwoWay}"
         Content="RadioButton 1" Height="71" Name="radioButton1"
         GroupName="RadioButtonGroup"  Margin="20,260,0,0" VerticalAlignment="Top"/>
                    <RadioButton IsChecked="{Binding RadioButton1IsChecked, Mode=TwoWay}"
         Content="RadioButton 2" Height="71" Name="radioButton2"
        GroupName="RadioButtonGroup"  Margin="20,340,0,0" VerticalAlignment="Top"/>
</Grid>

我们需要实现在应用逻辑删除后能将其状态保持到页面的State字典中，但是需要我们的数据源支持序列化，所以我们定义与表单关联的ViewModel如下：

[C#]
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[DataContract]
public class ViewModel : INotifyPropertyChanged
{
    private string _textBox1Text;
    private bool _checkBox1IsChecked;
    private bool _radioButton1IsChecked;
    private bool _radioButton2IsChecked;
    private double _slider1Value;
 
    [DataMember]
    public string TextBox1Text
    {
        get { return _textBox1Text; }
        set
        {
            _textBox1Text = value;
            NotifyPropertyChanged("TextBox1Text");
        }
    }
 
    [DataMember]
    public bool CheckBox1IsChecked
    {
        get { return _checkBox1IsChecked; }
        set
        {
            _checkBox1IsChecked = value;
            NotifyPropertyChanged("CheckBox1IsChecked");
        }
    }
 
    [DataMember]
    public double Slider1Value
    {
        get { return _slider1Value; }
        set
        {
            _slider1Value = value;
            NotifyPropertyChanged("Slider1Value");
        }
    }
 
    [DataMember]
    public bool RadioButton1IsChecked
    {
        get { return _radioButton1IsChecked; }
        set
        {
            _radioButton1IsChecked = value;
            NotifyPropertyChanged("RadioButton1IsChecked");
        }
    }
 
    [DataMember]
    public bool RadioButton2IsChecked
    {
        get { return _radioButton2IsChecked; }
        set
        {
            _radioButton2IsChecked = value;
            NotifyPropertyChanged("RadioButton2IsChecked");
        }
    }
 
    public event PropertyChangedEventHandler PropertyChanged;
 
    private void NotifyPropertyChanged(string propertyName)
    {
        if (null != PropertyChanged)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
 
}

我需要对mainpage代码添加页面导航入、导航出的事件。导航出页面的时候，如果不是向后导航，则存储状态。导航入的时候，我们需要判断页面是否为逻辑删除后正在恢复的状态，如果是，则通过状态字典恢复状态。mainpage代码如下：

[C#]
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public partial class MainPage : PhoneApplicationPage
{
    // 构造函数
    public MainPage()
    {
        InitializeComponent();
        _isNewPageInstance = true;
    }
 
    ViewModel _viewModel = null;
 
    /// <summary>
    /// 新实例还是现有实例
    /// </summary>
    bool _isNewPageInstance = false;
 
    private void Button_Click_1(object sender, RoutedEventArgs e)
    {
        NavigationService.Navigate(new Uri("/Page1.xaml", UriKind.Relative));
    }
 
    protected override void OnNavigatedFrom(System.Windows.Navigation.NavigationEventArgs e)
    {
        //如果不是向后导航，则保存状态
        if (e.NavigationMode != System.Windows.Navigation.NavigationMode.Back)
        {
            State["ViewModel"] = _viewModel;
 
        }
    }
 
    protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {
        if (_isNewPageInstance)
        {
            if (_viewModel == null)
            {
                if (State.Count > 0)
                {
                    _viewModel = (ViewModel)State["ViewModel"];
                }
                else
                {
                    _viewModel = new ViewModel();
                }
            }
            DataContext = _viewModel;
        }
        _isNewPageInstance = false;
    }
 
 
 
}

然后我们添加一page1页面，该页添加一个返回按钮。用于测试。为了达到调试时即时进入逻辑删除的效果，我们需要设置下。右键项目文件，点属性，在调试选项卡勾选“在调试期间取消激活时逻辑删除”。

 

二、后台代理

后台代理可以在应用退出以后独立在系统后台运行，它包含两种类型的代理，分别是定期代理和资源密集型代理，前者用于频繁执行小任务，后者用于在系统空闲时执行耗时大任务。要使用后台代理，我们需要添加一个名为Windows phone 计划任务代理的项目，并在应用的项目中添加对其的引用，现在我们要实现在后台代理中弹出Toast，我们需要如下修改ScheduledAgent.cs的OnInvoke方法，代码如下

[C#]
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protected override void OnInvoke(ScheduledTask task)
{
    string toastMessage = "";
 
    if (task is PeriodicTask)
    {
        toastMessage = "定期代理正在运行";
    }
    else
    {
        toastMessage = "资源密集型代理正在运行";
    }
 
    // 用于向用户显示Toast，如果当前任务的前台正在运行，则不显示
    ShellToast toast = new ShellToast();
    toast.Title = "标题";
    toast.Content = toastMessage;
    toast.Show();
 
    // 在调试的时候需要及时执行查看效果
    #if DEBUG_AGENT
        ScheduledActionService.LaunchForTest(task.Name, TimeSpan.FromSeconds(15));
    #endif
 
    NotifyComplete();
}

接着，我们在应用项目的mainpage中调用代理，代码如下：

[XAML]
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<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
    <StackPanel>
        <StackPanel  Orientation="Vertical" Name="PeriodicStackPanel" Margin="0,0,0,40">
            <TextBlock Text="定期代理" Style="{StaticResource PhoneTextTitle2Style}"/>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="名称: " Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding Name}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="是否可用" VerticalAlignment="Center"  Style="{StaticResource PhoneTextAccentStyle}"/>
                <CheckBox Name="PeriodicCheckBox" IsChecked="{Binding IsEnabled}" Checked="PeriodicCheckBox_Checked" Unchecked="PeriodicCheckBox_Unchecked"/>
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="是否已计划： "  Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding IsScheduled}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="上次计划运行时间： "  Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding LastScheduledTime}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="计划结束时间： " Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding ExpirationTime}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="上一次代理运行退出的原因： "  Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding LastExitReason}" />
            </StackPanel>
        </StackPanel>
        <StackPanel  Orientation="Vertical" Name="ResourceIntensiveStackPanel" Margin="0,0,0,40">
            <TextBlock Text="资源密集型代理" Style="{StaticResource PhoneTextTitle2Style}"/>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="名称: " Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding Name}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="是否可用" VerticalAlignment="Center"  Style="{StaticResource PhoneTextAccentStyle}"/>
                <CheckBox Name="ResourceIntensiveCheckBox" IsChecked="{Binding IsEnabled}" Checked="ResourceIntensiveCheckBox_Checked" Unchecked="ResourceIntensiveCheckBox_Unchecked"/>
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="是否已计划： "  Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding IsScheduled}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="上次计划运行时间： "  Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding LastScheduledTime}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="计划结束时间： " Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding ExpirationTime}" />
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="上一次代理运行退出的原因： "  Style="{StaticResource PhoneTextAccentStyle}"/>
                <TextBlock Text="{Binding LastExitReason}" />
            </StackPanel>
        </StackPanel>
    </StackPanel>
</Grid>
[C#]
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public partial class MainPage : PhoneApplicationPage
{
    /// <summary>
    /// 定期代理
    /// </summary>
    PeriodicTask periodicTask;
 
    /// <summary>
    /// 资源密集型代理
    /// </summary>
    ResourceIntensiveTask resourceIntensiveTask;
 
    string periodicTaskName = "PeriodicAgent";
    string resourceIntensiveTaskName = "ResourceIntensiveAgent";
 
    public bool agentsAreEnabled = true;
 
    // 构造函数
    public MainPage()
    {
        InitializeComponent();
    }
    //启动定期代理
    private void StartPeriodicAgent()
    {
        agentsAreEnabled = true;
 
        // 获取当前名称的定期代理，如果存在则移除
        periodicTask = ScheduledActionService.Find(periodicTaskName) as PeriodicTask;
        if (periodicTask != null)
        {
            RemoveAgent(periodicTaskName);
        }
 
        periodicTask = new PeriodicTask(periodicTaskName);
        periodicTask.Description = "这是一个定期代理的描述信息。";
        try
        {
            ScheduledActionService.Add(periodicTask);
            PeriodicStackPanel.DataContext = periodicTask;
 
            //在调试的时候需要及时执行查看效果
            #if(DEBUG_AGENT)
                ScheduledActionService.LaunchForTest(periodicTaskName, TimeSpan.FromSeconds(60));
            #endif
        }
        catch (InvalidOperationException exception)
        {
            if (exception.Message.Contains("BNS Error: The action is disabled"))
            {
                MessageBox.Show("本应用的后台计划被用户禁用。");
                agentsAreEnabled = false;
                PeriodicCheckBox.IsChecked = false;
            }
 
            if (exception.Message.Contains("BNS Error: The maximum number of ScheduledActions of this type have already been added."))
            {
                MessageBox.Show("定期代理数量达到最大限制。");
            }
            PeriodicCheckBox.IsChecked = false;
        }
        catch (SchedulerServiceException)
        {
            PeriodicCheckBox.IsChecked = false;
        }
    }
 
    private void StartResourceIntensiveAgent()
    {
        agentsAreEnabled = true;
 
        // 获取当前名称的资源密集型代理，如果存在则移除
        resourceIntensiveTask = ScheduledActionService.Find(resourceIntensiveTaskName) as ResourceIntensiveTask;
        if (resourceIntensiveTask != null)
        {
            RemoveAgent(resourceIntensiveTaskName);
        }
 
        resourceIntensiveTask = new ResourceIntensiveTask(resourceIntensiveTaskName);
        resourceIntensiveTask.Description = "这是一个资源密集型代理的描述信息。";
 
        try
        {
            ScheduledActionService.Add(resourceIntensiveTask);
            ResourceIntensiveStackPanel.DataContext = resourceIntensiveTask;
 
            //在调试的时候需要及时执行查看效果
            #if(DEBUG_AGENT)
                ScheduledActionService.LaunchForTest(resourceIntensiveTaskName, TimeSpan.FromSeconds(15));
            #endif
        }
        catch (InvalidOperationException exception)
        {
            if (exception.Message.Contains("BNS Error: The action is disabled"))
            {
                MessageBox.Show("本应用的后台计划被用户禁用。");
                agentsAreEnabled = false;
 
            }
            ResourceIntensiveCheckBox.IsChecked = false;
        }
        catch (SchedulerServiceException)
        {
            ResourceIntensiveCheckBox.IsChecked = false;
        }
    }
 
 
    bool ignoreCheckBoxEvents = false;
    private void PeriodicCheckBox_Checked(object sender, RoutedEventArgs e)
    {
        if (ignoreCheckBoxEvents)
            return;
        StartPeriodicAgent();
    }
    private void PeriodicCheckBox_Unchecked(object sender, RoutedEventArgs e)
    {
        if (ignoreCheckBoxEvents)
            return;
        RemoveAgent(periodicTaskName);
    }
    private void ResourceIntensiveCheckBox_Checked(object sender, RoutedEventArgs e)
    {
        if (ignoreCheckBoxEvents)
            return;
        StartResourceIntensiveAgent();
    }
    private void ResourceIntensiveCheckBox_Unchecked(object sender, RoutedEventArgs e)
    {
        if (ignoreCheckBoxEvents)
            return;
        RemoveAgent(resourceIntensiveTaskName);
    }
 
    /// <summary>
    /// 删除代理
    /// </summary>
    private void RemoveAgent(string name)
    {
        try
        {
            ScheduledActionService.Remove(name);
        }
        catch (Exception)
        {
        }
    }
 
    protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {
        ignoreCheckBoxEvents = true;
 
        periodicTask = ScheduledActionService.Find(periodicTaskName) as PeriodicTask;
 
        if (periodicTask != null)
        {
            PeriodicStackPanel.DataContext = periodicTask;
        }
 
        resourceIntensiveTask = ScheduledActionService.Find(resourceIntensiveTaskName) as ResourceIntensiveTask;
        if (resourceIntensiveTask != null)
        {
            ResourceIntensiveStackPanel.DataContext = resourceIntensiveTask;
        }
 
        ignoreCheckBoxEvents = false;
 
    }
 
}

 

三、后台音频

通过后台音频的功能我们可以实现在系统后台播放音乐的功能，由于后台音频代理只能访问本地文件夹，所以我们务必要先把需要播放的音乐文件拷贝到本地文件夹中。本示例是把安装文件夹的音频文件拷贝到本地文件夹，代码如下：

[C#]

我们需要在解决方案中添加Windows phone 音频播放代理项目，并在应用项目中添加对其的引用。修改AudioPlayer.cs代码如下：

[C#]

最后，我们在mainpage中添加对播放的控制。

[XAML]
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<Grid x:Name="LayoutRoot" Background="Transparent">
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>
     
 
    <!--TitlePanel 包含应用程序的名称和页标题-->
    <StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
        <TextBlock x:Name="ApplicationTitle" Text="后台音频" Style="{StaticResource PhoneTextNormalStyle}"/>
    </StackPanel>
 
    <!--ContentPanel - 在此处放置其他内容-->
    <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
        <Button x:Name="button2" Content="〈" HorizontalAlignment="Left" Margin="13,10,0,0" VerticalAlignment="Top" Click="Button_Click_2"/>
        <Button x:Name="button1" Content="▶" HorizontalAlignment="Left" Margin="75,10,0,0" VerticalAlignment="Top" Click="Button_Click_1"/>
        <Button x:Name="button3" Content="〉" HorizontalAlignment="Left" Margin="136,10,0,0" VerticalAlignment="Top" Click="Button_Click_3" />
        <TextBlock x:Name="textblock1" HorizontalAlignment="Left" Margin="22,87,0,0" TextWrapping="Wrap" VerticalAlignment="Top"/>
        <Image x:Name="imge1" HorizontalAlignment="Left" Height="100" Margin="22,142,0,0" VerticalAlignment="Top" Width="100"/>
 
    </Grid>
   </Grid>
[C#]
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public partial class MainPage : PhoneApplicationPage
{
    // 构造函数
    public MainPage()
    {
        InitializeComponent();
        BackgroundAudioPlayer.Instance.PlayStateChanged += new EventHandler(Instance_PlayStateChanged);
    }
 
    //刚加载时确定播放状态
    protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        if (PlayState.Playing == BackgroundAudioPlayer.Instance.PlayerState)
        {
            button1.Content = "■";
            textblock1.Text = "曲目：" + BackgroundAudioPlayer.Instance.Track.Title
                + " 艺术家：" + BackgroundAudioPlayer.Instance.Track.Artist
                + " 专辑：" + BackgroundAudioPlayer.Instance.Track.Album
                + " 曲目长度：" +BackgroundAudioPlayer.Instance.Track.Duration.Minutes + ":" + BackgroundAudioPlayer.Instance.Track.Duration.Seconds;
 
                using (IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication())
                {
                    var stream = storage.OpenFile(BackgroundAudioPlayer.Instance.Track.AlbumArt.OriginalString, System.IO.FileMode.Open);
                    var bitmapImage = new BitmapImage();
                    bitmapImage.SetSource(stream);
                    imge1.Source = bitmapImage;
                    stream.Close();
                }
        }
        else
        {
            button1.Content = "▶";
            textblock1.Text = "未播放曲目";
        }
    }
 
    void Instance_PlayStateChanged(object sender, EventArgs e)
    {
        switch (BackgroundAudioPlayer.Instance.PlayerState)
        {
            case PlayState.Playing:
                button1.Content = "■";
                button2.IsEnabled = true;
                button3.IsEnabled = true;
                break;
 
            case PlayState.Paused:
            case PlayState.Stopped:
                button1.Content = "▶";
                break;
        }
 
        if (null != BackgroundAudioPlayer.Instance.Track && BackgroundAudioPlayer.Instance.PlayerState!= PlayState.Stopped)
        {
            textblock1.Text = "曲目：" + BackgroundAudioPlayer.Instance.Track.Title
                + " 艺术家：" + BackgroundAudioPlayer.Instance.Track.Artist
                + " 专辑：" + BackgroundAudioPlayer.Instance.Track.Album
                + " 曲目长度：" + BackgroundAudioPlayer.Instance.Track.Duration.Minutes + ":" + BackgroundAudioPlayer.Instance.Track.Duration.Seconds;
 
                using (IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication())
                {
                    var stream = storage.OpenFile(BackgroundAudioPlayer.Instance.Track.AlbumArt.OriginalString, System.IO.FileMode.Open);
                    var bitmapImage = new BitmapImage();
                    bitmapImage.SetSource(stream);
                    imge1.Source = bitmapImage;
                    stream.Close();
                }
        }
    }
 
 
    //播放/暂停
    private void Button_Click_1(object sender, RoutedEventArgs e)
    {
        if (PlayState.Playing == BackgroundAudioPlayer.Instance.PlayerState)
            BackgroundAudioPlayer.Instance.Pause();
        else
            BackgroundAudioPlayer.Instance.Play();
    }
 
    //向前
    private void Button_Click_2(object sender, RoutedEventArgs e)
    {
        BackgroundAudioPlayer.Instance.SkipPrevious();
        button2.IsEnabled = false;
    }
    //向后
    private void Button_Click_3(object sender, RoutedEventArgs e)
    {
        BackgroundAudioPlayer.Instance.SkipNext();
        button3.IsEnabled = false;
    }
}

 

四、后台文件传输

后台文件传输允许我们实现下载上传文件的功能，他限制系统中同时运行的传输任务不能超过两个，并且下载的文件只能存放在本地文件夹的/shared/transfers目录下。下面我们实现一个后台传输任务，下载博客相册中的一张照片。

[XAML]
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<Grid x:Name="LayoutRoot" Background="Transparent">
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>
 
    <!--TitlePanel 包含应用程序的名称和页标题-->
    <StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
        <TextBlock x:Name="ApplicationTitle" Text="后台传输" Style="{StaticResource PhoneTextNormalStyle}"/>
    </StackPanel>
 
    <!--ContentPanel - 在此处放置其他内容-->
    <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
        <TextBlock x:Name="textblock1" HorizontalAlignment="Left" Margin="10,198,0,0" TextWrapping="Wrap" VerticalAlignment="Top"/>
        <Button Content="清除传输队列中已完成的任务" HorizontalAlignment="Left" Margin="0,85,0,0" VerticalAlignment="Top" Click="Button_Click_2"/>
    </Grid>
    <Button x:Name="button1" Content="添加一个后台传输" HorizontalAlignment="Left" Margin="12,10,0,0" Grid.Row="1" VerticalAlignment="Top" Click="Button_Click_1"/>
</Grid>
[C#]
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public partial class MainPage : PhoneApplicationPage
{
    // 构造函数
    public MainPage()
    {
        InitializeComponent();
    }
 
    protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {
 
        initTransferRequest();
        base.OnNavigatedTo(e);
    }
 
    private void initTransferRequest()
    {
        //获取第一个后台传输任务
        var transferRequest = BackgroundTransferService.Requests.FirstOrDefault();
        if (transferRequest == null)
        {
            textblock1.Text = "无后台传输任务";
            button1.IsEnabled = true;
            return;
        }
 
        //当传输状态改变时：
        transferRequest.TransferStatusChanged += new EventHandler<BackgroundTransferEventArgs>(transfer_TransferStatusChanged);
        //当传输进度改变时：
        transferRequest.TransferProgressChanged += new EventHandler<BackgroundTransferEventArgs>(transfer_TransferProgressChanged);
        updatesStatus(transferRequest);
        button1.IsEnabled = false;
    }
 
    void transfer_TransferStatusChanged(object sender, BackgroundTransferEventArgs e)
    {
        updatesStatus(e.Request);
    }
 
    void transfer_TransferProgressChanged(object sender, BackgroundTransferEventArgs e)
    {
        updatesStatus(e.Request);
    }
 
 
    void updatesStatus(BackgroundTransferRequest transferRequest)
    {
        textblock1.Text = "传输状态：" + transferRequest.TransferStatus.ToString()
            + " 已下载字节：" + transferRequest.BytesReceived
            + "总字节：" + transferRequest.TotalBytesToReceive;
    }
 
    private void Button_Click_1(object sender, RoutedEventArgs e)
    {
        string fileurlstring = "http://images.cnblogs.com/cnblogs_com/lipan/319399/o_Large.png";
        Uri uri = new Uri(Uri.EscapeUriString(fileurlstring), UriKind.RelativeOrAbsolute);
        BackgroundTransferRequest transferRequest = new BackgroundTransferRequest(uri);
        transferRequest.Method = "GET";
 
        using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication())
        {
            if (!isoStore.DirectoryExists("/shared/transfers"))
            {
                isoStore.CreateDirectory("/shared/transfers");
            }
        }
 
        //文件下载后存放位置（为本地文件夹相对位置）
        transferRequest.DownloadLocation = new Uri("shared/transfers/1.png", UriKind.RelativeOrAbsolute);
        //外接电源、WiFi的可用性对传输的影响
        transferRequest.TransferPreferences = TransferPreferences.AllowCellularAndBattery;
 
        try
        {
            //添加到后台传输队列中
            BackgroundTransferService.Add(transferRequest);
        }
        catch (Exception ex)
        {
            MessageBox.Show("无法添加后台传输请求。" + ex.Message);
        }
        initTransferRequest();
    }
 
    //清除传输队列已完成的任务
    private void Button_Click_2(object sender, RoutedEventArgs e)
    {
        foreach (var transferRequest in BackgroundTransferService.Requests)
        {
            if (transferRequest.TransferStatus == TransferStatus.Completed)
            {
                try
                {
                    BackgroundTransferService.Remove(transferRequest);
                }
                catch
                {
                }
            }
        }
        initTransferRequest();
    }
 
}

 

五、后台辅助线程

后台辅助线程虽然名字这么叫，但是它不能在后台运行，我们可以用它来执行一个任务，并且可以实时获取执行的进度，实现代码如下：

[XAML]
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<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
    <StackPanel>
        <StackPanel Orientation="Horizontal"
                HorizontalAlignment="Left" VerticalAlignment="Top"
                Margin="10" >
            <Button x:Name="buttonStart" Content="开始" Click="buttonStart_Click"
                Width="200" />
            <Button x:Name="buttonCancel" Content="取消" Click="buttonCancel_Click"
                Width="200" />
        </StackPanel>
        <StackPanel Margin="10,50,0,0" Orientation="Horizontal">
            <TextBlock Text="进度: " />
            <TextBlock x:Name="tbProgress" />
        </StackPanel>
    </StackPanel>
 
</Grid>
[C#]
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public partial class MainPage : PhoneApplicationPage
{
         
      private BackgroundWorker bw = new BackgroundWorker();
 
      public MainPage()
    {
        InitializeComponent();
 
        bw.WorkerReportsProgress = true;
        bw.WorkerSupportsCancellation = true;
        bw.DoWork += new DoWorkEventHandler(bw_DoWork);
        bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
        bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
    }
    private void buttonStart_Click(object sender, RoutedEventArgs e)
    {
        if (bw.IsBusy != true)
        {
            bw.RunWorkerAsync();
        }
    }
    private void buttonCancel_Click(object sender, RoutedEventArgs e)
    {
        if (bw.WorkerSupportsCancellation == true)
        {
            bw.CancelAsync();
        }
    }
    private void bw_DoWork(object sender, DoWorkEventArgs e)
    {
        BackgroundWorker worker = sender as BackgroundWorker;
 
        for (int i = 1; i <= 10; i++)
        {
            if ((worker.CancellationPending == true))
            {
                e.Cancel = true;
                break;
            }
            else
            {
                // Perform a time consuming operation and report progress.
                System.Threading.Thread.Sleep(500);
                worker.ReportProgress(i * 10);
            }
        }
    }
    private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        if (e.Cancelled == true)
        {
            this.tbProgress.Text = "Canceled!";
        }
 
        else if (!(e.Error == null))
        {
            this.tbProgress.Text = ("Error: " + e.Error.Message);
        }
 
        else
        {
            this.tbProgress.Text = "Done!";
        }
    }
    private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        this.tbProgress.Text = (e.ProgressPercentage.ToString() + "%");
    }
}

 

作者：[Lipan]
出处：[http://www.cnblogs.com/lipan/]
版权声明：本文的版权归作者与博客园共有。转载时须注明原文出处以及作者，并保留原文指向型链接，不得更改原文内容。否则作者将保留追究其法律责任。
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