首页 > 代码库 > Windows phone 8 学习笔记(6) 多任务（转）
Windows phone 8 学习笔记(6) 多任务（转）
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]
<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="http://www.mamicode.com/{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#]
[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 = http://www.mamicode.com/value;"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#]
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#]
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]
<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#]
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#]
//把安装文件夹下的文件拷贝到本地文件夹 private void CopyToIsolatedStorage() { using (IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication()) { string[] files = new string[] { "Ring01.wma", "Ring02.wma", "Ring03.wma" }; foreach (var _fileName in files) { if (!storage.FileExists(_fileName)) { string _filePath = "Audio/" + _fileName; StreamResourceInfo resource = Application.GetResourceStream(new Uri(_filePath, UriKind.Relative)); using (IsolatedStorageFileStream file = storage.CreateFile(_fileName)) { int chunkSize = 4096; byte[] bytes = new byte[chunkSize]; int byteCount; while ((byteCount = resource.Stream.Read(bytes, 0, chunkSize)) > 0) { file.Write(bytes, 0, byteCount); } } } } string[] icons = new string[] { "Ring01.jpg", "Ring02.jpg", "Ring03.jpg" }; foreach (var _fileName in icons) { if (!storage.FileExists(_fileName)) { string _filePath = "Images/" + _fileName; StreamResourceInfo iconResource = Application.GetResourceStream(new Uri(_filePath, UriKind.Relative)); using (IsolatedStorageFileStream file = storage.CreateFile( _fileName)) { int chunkSize = 4096; byte[] bytes = new byte[chunkSize]; int byteCount; while ((byteCount = iconResource.Stream.Read(bytes, 0, chunkSize)) > 0) { file.Write(bytes, 0, byteCount); } } } } } }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#]
public class AudioPlayer : AudioPlayerAgent { private static volatile bool _classInitialized; private static List<AudioTrack> _playList = new List<AudioTrack> { new AudioTrack(new Uri("Ring01.wma", UriKind.Relative),"曲目1","艺术家1","专辑1",new Uri("Ring01.jpg", UriKind.Relative)), new AudioTrack(new Uri("Ring02.wma", UriKind.Relative),"曲目2","艺术家2","专辑2",new Uri("Ring02.jpg", UriKind.Relative)), new AudioTrack(new Uri("Ring03.wma", UriKind.Relative),"曲目3","艺术家3","专辑3",new Uri("Ring03.jpg", UriKind.Relative)) }; /// <summary> /// 当前播放位置 /// </summary> static int currentTrackNumber = 0; /// <remarks> /// AudioPlayer 实例可共享同一进程。 /// 静态字段可用于在 AudioPlayer 实例之间共享状态 /// 或与音频流代理通信。 /// </remarks> public AudioPlayer() { if (!_classInitialized) { _classInitialized = true; // 订阅托管异常处理程序 Deployment.Current.Dispatcher.BeginInvoke(delegate { Application.Current.UnhandledException += AudioPlayer_UnhandledException; }); } } /// 出现未处理的异常时执行的代码 private void AudioPlayer_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e) { if (System.Diagnostics.Debugger.IsAttached) { // 出现未处理的异常；强行进入调试器 System.Diagnostics.Debugger.Break(); } } /// <summary> /// playstate 更改时调用，但 Error 状态除外(参见 one rror) /// </summary> /// <param name="player">BackgroundAudioPlayer</param> /// <param name="track">在 playstate 更改时播放的曲目</param> /// <param name="playState">播放机的新 playstate </param> /// <remarks> /// 无法取消播放状态更改。即使应用程序 /// 导致状态自行更改，假定应用程序已经选择了回调。 /// /// 值得注意的 playstate 事件 /// (a) TrackEnded: 播放器没有当前曲目时激活。代理可设置下一曲目。 /// (b) TrackReady: 音轨已设置完毕，现在可以播放。 /// /// 只在代理请求完成之后调用一次 NotifyComplete()，包括异步回调。 /// </remarks> protected override void OnPlayStateChanged(BackgroundAudioPlayer player, AudioTrack track, PlayState playState) { switch (playState) { case PlayState.TrackEnded: player.Track = GetPreviousTrack(); break; case PlayState.TrackReady: player.Play(); break; case PlayState.Shutdown: // TODO: 在此处理关机状态(例如保存状态) break; case PlayState.Unknown: break; case PlayState.Stopped: break; case PlayState.Paused: break; case PlayState.Playing: break; case PlayState.BufferingStarted: break; case PlayState.BufferingStopped: break; case PlayState.Rewinding: break; case PlayState.FastForwarding: break; } NotifyComplete(); } /// <summary> /// 在用户使用应用程序/系统提供的用户界面请求操作时调用 /// </summary> /// <param name="player">BackgroundAudioPlayer</param> /// <param name="track">用户操作期间播放的曲目</param> /// <param name="action">用户请求的操作</param> /// <param name="param">与请求的操作相关联的数据。 /// 在当前版本中，此参数仅适合与 Seek 操作一起使用， /// 以指明请求的乐曲的位置</param> /// <remarks> /// 用户操作不自动对系统状态进行任何更改；如果用户操作受支持， /// 执行用户操作(如果这些操作受支持)。 /// /// 只在代理请求完成之后调用一次 NotifyComplete()，包括异步回调。 /// </remarks> protected override void OnUserAction(BackgroundAudioPlayer player, AudioTrack track, UserAction action, object param) { switch (action) { case UserAction.Play: if (player.PlayerState != PlayState.Playing) { player.Play(); } break; case UserAction.Stop: player.Stop(); break; case UserAction.Pause: player.Pause(); break; case UserAction.FastForward: player.FastForward(); break; case UserAction.Rewind: player.Rewind(); break; case UserAction.Seek: player.Position = (TimeSpan)param; break; case UserAction.SkipNext: player.Track = GetNextTrack(); break; case UserAction.SkipPrevious: AudioTrack previousTrack = GetPreviousTrack(); if (previousTrack != null) { player.Track = previousTrack; } break; } NotifyComplete(); } /// <summary> /// 实现逻辑以获取下一个 AudioTrack 实例。 /// 在播放列表中，源可以是文件、Web 请求，等等。 /// </summary> /// <remarks> /// AudioTrack URI 确定源，它可以是: /// (a) 独立存储器文件(相对 URI，表示独立存储器中的路径) /// (b) HTTP URL(绝对 URI) /// (c) MediaStreamSource (null) /// </remarks> /// <returns>AudioTrack 实例，或如果播放完毕，则返回 null</returns> private AudioTrack GetNextTrack() { // TODO: 添加逻辑以获取下一条音轨 if (++currentTrackNumber >= _playList.Count) currentTrackNumber = 0; AudioTrack track = _playList[currentTrackNumber]; // 指定曲目 return track; } /// <summary> /// 实现逻辑以获取前一个 AudioTrack 实例。 /// </summary> /// <remarks> /// AudioTrack URI 确定源，它可以是: /// (a) 独立存储器文件(相对 URI，表示独立存储器中的路径) /// (b) HTTP URL(绝对 URI) /// (c) MediaStreamSource (null) /// </remarks> /// <returns>AudioTrack 实例，或如果不允许前一曲目，则返回 null</returns> private AudioTrack GetPreviousTrack() { // TODO: 添加逻辑以获取前一条音轨 if (--currentTrackNumber < 0) currentTrackNumber = _playList.Count - 1; AudioTrack track = _playList[currentTrackNumber]; // 指定曲目 return track; } /// <summary> /// 每次播放出错(如 AudioTrack 未正确下载)时调用 /// </summary> /// <param name="player">BackgroundAudioPlayer</param> /// <param name="track">出现错误的曲目</param> /// <param name="error">出现的错误</param> /// <param name="isFatal">如果为 true，则播放不能继续并且曲目播放将停止</param> /// <remarks> /// 不保证在所有情况下都调用此方法。例如，如果后台代理程序 /// 本身具有未处理的异常，则不会回调它来处理它自己的错误。 /// </remarks> protected override void one rror(BackgroundAudioPlayer player, AudioTrack track, Exception error, bool isFatal) { if (isFatal) { Abort(); } else { NotifyComplete(); } } /// <summary> /// 取消代理请求时调用 /// </summary> /// <remarks> /// 取消请求后，代理需要 5 秒钟完成其工作， /// 通过调用 NotifyComplete()/Abort()。 /// </remarks> protected override void OnCancel() { } }最后，我们在mainpage中添加对播放的控制。
[XAML]
<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#]
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]
<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#]
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]
<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#]
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() + "%"); } }
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