Windows phone 8 是一個單任務操作系統，任何時候都只有一個應用處於活躍狀態，這里的多任務是指對后台任務的支持。本節我們先講講應用程序的運行狀態，然后看看支持的后台任務，包括：后台代理、后台音頻、后台文件傳輸、后台輔助線程等。
快速導航：
一、應用的狀態
二、后台代理
三、后台音頻
四、后台文件傳輸
五、后台輔助線程
一、應用的狀態
1）應用的運行狀態
我們通過圖解來分析應用的運行狀態，啟動並置於前台界面的應用是唯一處於運行狀態的，其他的操作，比如win鍵，后退導出應用，打開選擇器和啟動器時都會讓當前運行的應用進入休眠狀態，如果系統內存不足，處於休眠狀態的應用可能會被系統邏輯刪除。下面的圖示演示了這個過程。
2）如何恢復狀態
當應用處於休眠狀態時，它的狀態信息仍然保留在內存中，用戶下次切換進去后不會有任何變化。但是當應用被邏輯刪除后，這些狀態信息就會丟失，比如表單填寫的內容都會消失，為了避免這種情況，我們需要手動保留狀態信息。
首先，我們在mainpage定義一些頁面表單控件：
<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>
我們需要實現在應用邏輯刪除后能將其狀態保持到頁面的State字典中，但是需要我們的數據源支持序列化，所以我們定義與表單關聯的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 = 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));
}
}
我需要對mainpage代碼添加頁面導航入、導航出的事件。導航出頁面的時候，如果不是向后導航，則存儲狀態。導航入的時候，我們需要判斷頁面是否為邏輯刪除后正在恢復的狀態，如果是，則通過狀態字典恢復狀態。mainpage代碼如下：
[C#] public partial class MainPage : PhoneApplicationPage
{
// 構造函數
public MainPage()
{
InitializeComponent();
_isNewPageInstance = true;
}
ViewModel _viewModel = null;
/// <summary>
/// 新實例還是現有實例
/// </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)
{
//如果不是向后導航，則保存狀態
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;
}
}
然后我們添加一page1頁面，該頁添加一個返回按鈕。用於測試。為了達到調試時即時進入邏輯刪除的效果，我們需要設置下。右鍵項目文件，點屬性，在調試選項卡勾選“在調試期間取消激活時邏輯刪除”。
二、后台代理
后台代理可以在應用退出以后獨立在系統后台運行，它包含兩種類型的代理，分別是定期代理和資源密集型代理，前者用於頻繁執行小任務，后者用於在系統空閑時執行耗時大任務。要使用后台代理，我們需要添加一個名為Windows phone 計划任務代理的項目，並在應用的項目中添加對其的引用，現在我們要實現在后台代理中彈出Toast，我們需要如下修改ScheduledAgent.cs的OnInvoke方法，代碼如下
[C#] protected override void OnInvoke(ScheduledTask task)
{
string toastMessage = "";
if (task is PeriodicTask)
{
toastMessage = "定期代理正在運行";
}
else
{
toastMessage = "資源密集型代理正在運行";
}
// 用於向用戶顯示Toast，如果當前任務的前台正在運行，則不顯示
ShellToast toast = new ShellToast();
toast.Title = "標題";
toast.Content = toastMessage;
toast.Show();
// 在調試的時候需要及時執行查看效果
#if DEBUG_AGENT
ScheduledActionService.LaunchForTest(task.Name, TimeSpan.FromSeconds(15));
#endif
NotifyComplete();
}
接着，我們在應用項目的mainpage中調用代理，代碼如下：
[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="名稱: " 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="是否已計划： " Style="{StaticResource PhoneTextAccentStyle}"/>
<TextBlock Text="{Binding IsScheduled}" />
</StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="上次計划運行時間： " Style="{StaticResource PhoneTextAccentStyle}"/>
<TextBlock Text="{Binding LastScheduledTime}" />
</StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="計划結束時間： " Style="{StaticResource PhoneTextAccentStyle}"/>
<TextBlock Text="{Binding ExpirationTime}" />
</StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="上一次代理運行退出的原因： " Style="{StaticResource PhoneTextAccentStyle}"/>
<TextBlock Text="{Binding LastExitReason}" />
</StackPanel>
</StackPanel>
<StackPanel Orientation="Vertical" Name="ResourceIntensiveStackPanel" Margin="0,0,0,40">
<TextBlock Text="資源密集型代理" Style="{StaticResource PhoneTextTitle2Style}"/>
<StackPanel Orientation="Horizontal">
<TextBlock Text="名稱: " 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="是否已計划： " Style="{StaticResource PhoneTextAccentStyle}"/>
<TextBlock Text="{Binding IsScheduled}" />
</StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="上次計划運行時間： " Style="{StaticResource PhoneTextAccentStyle}"/>
<TextBlock Text="{Binding LastScheduledTime}" />
</StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="計划結束時間： " Style="{StaticResource PhoneTextAccentStyle}"/>
<TextBlock Text="{Binding ExpirationTime}" />
</StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="上一次代理運行退出的原因： " Style="{StaticResource PhoneTextAccentStyle}"/>
<TextBlock Text="{Binding LastExitReason}" />
</StackPanel>
</StackPanel>
</StackPanel>
</Grid>
public partial class MainPage : PhoneApplicationPage
{
/// <summary>
/// 定期代理
/// </summary>
PeriodicTask periodicTask;
/// <summary>
/// 資源密集型代理
/// </summary>
ResourceIntensiveTask resourceIntensiveTask;
string periodicTaskName = "PeriodicAgent";
string resourceIntensiveTaskName = "ResourceIntensiveAgent";
public bool agentsAreEnabled = true;
// 構造函數
public MainPage()
{
InitializeComponent();
}
//啟動定期代理
private void StartPeriodicAgent()
{
agentsAreEnabled = true;
// 獲取當前名稱的定期代理，如果存在則移除
periodicTask = ScheduledActionService.Find(periodicTaskName) as PeriodicTask;
if (periodicTask != null)
{
RemoveAgent(periodicTaskName);
}
periodicTask = new PeriodicTask(periodicTaskName);
periodicTask.Description = "這是一個定期代理的描述信息。";
try
{
ScheduledActionService.Add(periodicTask);
PeriodicStackPanel.DataContext = periodicTask;
//在調試的時候需要及時執行查看效果
#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("本應用的后台計划被用戶禁用。");
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("定期代理數量達到最大限制。");
}
PeriodicCheckBox.IsChecked = false;
}
catch (SchedulerServiceException)
{
PeriodicCheckBox.IsChecked = false;
}
}
private void StartResourceIntensiveAgent()
{
agentsAreEnabled = true;
// 獲取當前名稱的資源密集型代理，如果存在則移除
resourceIntensiveTask = ScheduledActionService.Find(resourceIntensiveTaskName) as ResourceIntensiveTask;
if (resourceIntensiveTask != null)
{
RemoveAgent(resourceIntensiveTaskName);
}
resourceIntensiveTask = new ResourceIntensiveTask(resourceIntensiveTaskName);
resourceIntensiveTask.Description = "這是一個資源密集型代理的描述信息。";
try
{
ScheduledActionService.Add(resourceIntensiveTask);
ResourceIntensiveStackPanel.DataContext = resourceIntensiveTask;
//在調試的時候需要及時執行查看效果
#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("本應用的后台計划被用戶禁用。");
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>
/// 刪除代理
/// </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、后台音頻
通過后台音頻的功能我們可以實現在系統后台播放音樂的功能，由於后台音頻代理只能訪問本地文件夾，所以我們務必要先把需要播放的音樂文件拷貝到本地文件夾中。本示例是把安裝文件夾的音頻文件拷貝到本地文件夾，代碼如下：
[C#] //把安裝文件夾下的文件拷貝到本地文件夾
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);
}
}
}
}
}
}
我們需要在解決方案中添加Windows phone 音頻播放代理項目，並在應用項目中添加對其的引用。修改AudioPlayer.cs代碼如下：
[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","藝術家1","專輯1",new Uri("Ring01.jpg", UriKind.Relative)),
new AudioTrack(new Uri("Ring02.wma", UriKind.Relative),"曲目2","藝術家2","專輯2",new Uri("Ring02.jpg", UriKind.Relative)),
new AudioTrack(new Uri("Ring03.wma", UriKind.Relative),"曲目3","藝術家3","專輯3",new Uri("Ring03.jpg", UriKind.Relative))
};
/// <summary>
/// 當前播放位置
/// </summary>
static int currentTrackNumber = 0;
/// <remarks>
/// AudioPlayer 實例可共享同一進程。
/// 靜態字段可用於在 AudioPlayer 實例之間共享狀態
/// 或與音頻流代理通信。
/// </remarks>
public AudioPlayer()
{
if (!_classInitialized)
{
_classInitialized = true;
// 訂閱托管異常處理程序
Deployment.Current.Dispatcher.BeginInvoke(delegate
{
Application.Current.UnhandledException += AudioPlayer_UnhandledException;
});
}
}
/// 出現未處理的異常時執行的代碼
private void AudioPlayer_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
{
if (System.Diagnostics.Debugger.IsAttached)
{
// 出現未處理的異常；強行進入調試器
System.Diagnostics.Debugger.Break();
}
}
/// <summary>
/// playstate 更改時調用，但 Error 狀態除外(參見 OnError)
/// </summary>
/// <param name="player">BackgroundAudioPlayer</param>
/// <param name="track">在 playstate 更改時播放的曲目</param>
/// <param name="playState">播放機的新 playstate </param>
/// <remarks>
/// 無法取消播放狀態更改。即使應用程序
/// 導致狀態自行更改，假定應用程序已經選擇了回調。
///
/// 值得注意的 playstate 事件
/// (a) TrackEnded: 播放器沒有當前曲目時激活。代理可設置下一曲目。
/// (b) TrackReady: 音軌已設置完畢，現在可以播放。
///
/// 只在代理請求完成之后調用一次 NotifyComplete()，包括異步回調。
/// </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: 在此處理關機狀態(例如保存狀態)
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>
/// 在用戶使用應用程序/系統提供的用戶界面請求操作時調用
/// </summary>
/// <param name="player">BackgroundAudioPlayer</param>
/// <param name="track">用戶操作期間播放的曲目</param>
/// <param name="action">用戶請求的操作</param>
/// <param name="param">與請求的操作相關聯的數據。
/// 在當前版本中，此參數僅適合與 Seek 操作一起使用，
/// 以指明請求的樂曲的位置</param>
/// <remarks>
/// 用戶操作不自動對系統狀態進行任何更改；如果用戶操作受支持，
/// 執行用戶操作(如果這些操作受支持)。
///
/// 只在代理請求完成之后調用一次 NotifyComplete()，包括異步回調。
/// </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>
/// 實現邏輯以獲取下一個 AudioTrack 實例。
/// 在播放列表中，源可以是文件、Web 請求，等等。
/// </summary>
/// <remarks>
/// AudioTrack URI 確定源，它可以是:
/// (a) 獨立存儲器文件(相對 URI，表示獨立存儲器中的路徑)
/// (b) HTTP URL(絕對 URI)
/// (c) MediaStreamSource (null)
/// </remarks>
/// <returns>AudioTrack 實例，或如果播放完畢，則返回 null</returns>
private AudioTrack GetNextTrack()
{
// TODO: 添加邏輯以獲取下一條音軌
if (++currentTrackNumber >= _playList.Count) currentTrackNumber = 0;
AudioTrack track = _playList[currentTrackNumber];
// 指定曲目
return track;
}
/// <summary>
/// 實現邏輯以獲取前一個 AudioTrack 實例。
/// </summary>
/// <remarks>
/// AudioTrack URI 確定源，它可以是:
/// (a) 獨立存儲器文件(相對 URI，表示獨立存儲器中的路徑)
/// (b) HTTP URL(絕對 URI)
/// (c) MediaStreamSource (null)
/// </remarks>
/// <returns>AudioTrack 實例，或如果不允許前一曲目，則返回 null</returns>
private AudioTrack GetPreviousTrack()
{
// TODO: 添加邏輯以獲取前一條音軌
if (--currentTrackNumber < 0) currentTrackNumber = _playList.Count - 1;
AudioTrack track = _playList[currentTrackNumber];
// 指定曲目
return track;
}
/// <summary>
/// 每次播放出錯(如 AudioTrack 未正確下載)時調用
/// </summary>
/// <param name="player">BackgroundAudioPlayer</param>
/// <param name="track">出現錯誤的曲目</param>
/// <param name="error">出現的錯誤</param>
/// <param name="isFatal">如果為 true，則播放不能繼續並且曲目播放將停止</param>
/// <remarks>
/// 不保證在所有情況下都調用此方法。例如，如果后台代理程序
/// 本身具有未處理的異常，則不會回調它來處理它自己的錯誤。
/// </remarks>
protected override void OnError(BackgroundAudioPlayer player, AudioTrack track, Exception error, bool isFatal)
{
if (isFatal)
{
Abort();
}
else
{
NotifyComplete();
}
}
/// <summary>
/// 取消代理請求時調用
/// </summary>
/// <remarks>
/// 取消請求后，代理需要 5 秒鍾完成其工作，
/// 通過調用 NotifyComplete()/Abort()。
/// </remarks>
protected override void OnCancel()
{
}
}
最后，我們在mainpage中添加對播放的控制。
[XAML] <Grid x:Name="LayoutRoot" Background="Transparent">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<!--TitlePanel 包含應用程序的名稱和頁標題-->
<StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
<TextBlock x:Name="ApplicationTitle" Text="后台音頻" Style="{StaticResource PhoneTextNormalStyle}"/>
</StackPanel>
<!--ContentPanel - 在此處放置其他內容-->
<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>
public partial class MainPage : PhoneApplicationPage
{
// 構造函數
public MainPage()
{
InitializeComponent();
BackgroundAudioPlayer.Instance.PlayStateChanged += new EventHandler(Instance_PlayStateChanged);
}
//剛加載時確定播放狀態
protected override void OnNavigatedTo(NavigationEventArgs e)
{
if (PlayState.Playing == BackgroundAudioPlayer.Instance.PlayerState)
{
button1.Content = "■";
textblock1.Text = "曲目：" + BackgroundAudioPlayer.Instance.Track.Title
+ " 藝術家：" + BackgroundAudioPlayer.Instance.Track.Artist
+ " 專輯：" + BackgroundAudioPlayer.Instance.Track.Album
+ " 曲目長度：" +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
+ " 藝術家：" + BackgroundAudioPlayer.Instance.Track.Artist
+ " 專輯：" + BackgroundAudioPlayer.Instance.Track.Album
+ " 曲目長度：" + 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/暫停
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、后台文件傳輸
后台文件傳輸允許我們實現下載上傳文件的功能，他限制系統中同時運行的傳輸任務不能超過兩個，並且下載的文件只能存放在本地文件夾的/shared/transfers目錄下。下面我們實現一個后台傳輸任務，下載博客相冊中的一張照片。
[XAML] <Grid x:Name="LayoutRoot" Background="Transparent">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<!--TitlePanel 包含應用程序的名稱和頁標題-->
<StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
<TextBlock x:Name="ApplicationTitle" Text="后台傳輸" Style="{StaticResource PhoneTextNormalStyle}"/>
</StackPanel>
<!--ContentPanel - 在此處放置其他內容-->
<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="清除傳輸隊列中已完成的任務" HorizontalAlignment="Left" Margin="0,85,0,0" VerticalAlignment="Top" Click="Button_Click_2"/>
</Grid>
<Button x:Name="button1" Content="添加一個后台傳輸" HorizontalAlignment="Left" Margin="12,10,0,0" Grid.Row="1" VerticalAlignment="Top" Click="Button_Click_1"/>
</Grid>
public partial class MainPage : PhoneApplicationPage
{
// 構造函數
public MainPage()
{
InitializeComponent();
}
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
initTransferRequest();
base.OnNavigatedTo(e);
}
private void initTransferRequest()
{
//獲取第一個后台傳輸任務
var transferRequest = BackgroundTransferService.Requests.FirstOrDefault();
if (transferRequest == null)
{
textblock1.Text = "無后台傳輸任務";
button1.IsEnabled = true;
return;
}
//當傳輸狀態改變時：
transferRequest.TransferStatusChanged += new EventHandler<BackgroundTransferEventArgs>(transfer_TransferStatusChanged);
//當傳輸進度改變時：
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 = "傳輸狀態：" + transferRequest.TransferStatus.ToString()
+ " 已下載字節：" + transferRequest.BytesReceived
+ "總字節：" + 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");
}
}
//文件下載后存放位置（為本地文件夾相對位置）
transferRequest.DownloadLocation = new Uri("shared/transfers/1.png", UriKind.RelativeOrAbsolute);
//外接電源、WiFi的可用性對傳輸的影響
transferRequest.TransferPreferences = TransferPreferences.AllowCellularAndBattery;
try
{
//添加到后台傳輸隊列中
BackgroundTransferService.Add(transferRequest);
}
catch (Exception ex)
{
MessageBox.Show("無法添加后台傳輸請求。" + ex.Message);
}
initTransferRequest();
}
//清除傳輸隊列已完成的任務
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、后台輔助線程
后台輔助線程雖然名字這么叫，但是它不能在后台運行，我們可以用它來執行一個任務，並且可以實時獲取執行的進度，實現代碼如下：
[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="開始" 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="進度: " />
<TextBlock x:Name="tbProgress" />
</StackPanel>
</StackPanel>
</Grid>
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]
出處：[ http://www.cnblogs.com/lipan/]
版權聲明：本文的版權歸作者與博客園共有。轉載時須注明原文出處以及作者，並保留原文指向型鏈接，不得更改原文內容。否則作者將保留追究其法律責任。
出處：[ http://www.cnblogs.com/lipan/]
版權聲明：本文的版權歸作者與博客園共有。轉載時須注明原文出處以及作者，並保留原文指向型鏈接，不得更改原文內容。否則作者將保留追究其法律責任。