原文:與眾不同 windows phone (15) - Media（媒體）之后臺播放音頻

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與眾不同 windows phone (15) - Media（媒體）之后臺播放音頻

作者：webabcd


介紹
與眾不同 windows phone 7.5 (sdk 7.1) 之媒體

• 通過 AudioPlayerAgent 實現(xiàn)在后臺播放音頻

示例
演示如何通過后臺代理的方式來實現(xiàn)音頻在后臺的播放
1、后臺代理
MyAudioPlayerAgent/AudioPlayer.cs

/** 本例演示如何播放后臺音頻（以 AudioPlayerAgent 為例，另 AudioStreamingAgent 用于流式播放音頻）* 建議使用 AudioPlaybackAgent 類型的模板創(chuàng)建此項目* * BackgroundAgent - 后臺代理類，抽象類，它是 ScheduledTaskAgent、AudioPlayerAgent 和 AudioStreamingAgent 的基類* NotifyComplete() - 用于通知系統(tǒng)，代理已經(jīng)完成了當前的任務(wù)，調(diào)用此方法后，系統(tǒng)才會去準備執(zhí)行下一次任務(wù)* Abort() - 用于通知系統(tǒng)，放棄此次和以后的任務(wù)* OnCancel() - 后臺代理被取消時所執(zhí)行的方法（由系統(tǒng)調(diào)用，比如后臺代理轉(zhuǎn)到休眠狀態(tài)或終止狀態(tài)前會調(diào)用此方法）* * AudioPlayerAgent - 后臺播放音頻的代理類* OnError() - 當播放中出現(xiàn)錯誤時，系統(tǒng)會調(diào)用此方法* OnPlayStateChanged() - 當播放狀態(tài)發(fā)生改變時，系統(tǒng)會調(diào)用此方法（錯誤狀態(tài)除外）* OnUserAction() - 當程序改變播放行為時，系統(tǒng)會調(diào)用此方法* * PlayState - Microsoft.Phone.BackgroundAudio.PlayState 枚舉* Unknown, Stopped, Paused, Playing, BufferingStarted, BufferingStopped, TrackReady, TrackEnded, Rewinding, FastForwarding, Shutdown, Error* * UserAction - Microsoft.Phone.BackgroundAudio.UserAction 枚舉* Stop, Pause, Play, SkipNext, SkipPrevious, FastForward, Rewind, Seek* * AudioTrack - 音頻對象* Source - 音頻的地址，遠程地址或獨立存儲地址均可* Title - 音頻名稱* Duration - 音頻時長* Album - 專輯名稱* AlbumArt - 專輯封面的 Uri 地址，遠程地址或獨立存儲地址均可，如果使用獨立存儲地址則其目錄必須是 Shared/Media* Artist - 藝術(shù)家* PlayerControls - 鎖屏等狀態(tài)下的播放器控件顯示（Microsoft.Phone.BackgroundAudio.EnabledPlayerControls 枚舉）* None = 0, SkipNext = 1, SkipPrevious = 2, FastForward = 4, Rewind = 8, Pause = 16, All = 31* Tag - 任意內(nèi)容，即為 AudioTrack 綁定一個上下文數(shù)據(jù)* BeginEdit() - 將 AudioTrack 設(shè)置為編輯狀態(tài)（如果需要修改 AudioTrack 的屬性則需要將 AudioTrack 設(shè)置為編輯狀態(tài)）* EndEdit() - 結(jié)束 AudioTrack 的編輯狀態(tài)*/using System; using System.Windows; using Microsoft.Phone.BackgroundAudio;using System.Collections.Generic;namespace MyAudioPlayerAgent {public class AudioPlayer : AudioPlayerAgent{// 播放列表private static List<AudioTrack> _playList = new List<AudioTrack>{new AudioTrack(new Uri("SuperMario.mp3", UriKind.Relative), "title", "artist", "album", null, null, EnabledPlayerControls.Pause),new AudioTrack(new Uri("http://traffic.libsyn.com/wpradio/WPRadio_29.mp3", UriKind.Absolute), "標題", "藝術(shù)家", "專輯", null, null, EnabledPlayerControls.All)};// 當前播放的 Track 在整個播放列表中的位置private static int _currentTrackNumber = 0;/** _classInitialized - 用于標記 AudioPlayer 是否已經(jīng)被初始化* 標記成 volatile 是為了避免編譯器認為此字段無外部修改，而將其優(yōu)化放入寄存器（標記成 volatile 的字段只會放在內(nèi)存中）* 一般來說，多任務(wù)環(huán)境下各任務(wù)間共享的字段應(yīng)該被標記為 volatile*/private static volatile bool _classInitialized;public AudioPlayer(){if (!_classInitialized){_classInitialized = true;Deployment.Current.Dispatcher.BeginInvoke(delegate{Application.Current.UnhandledException += AudioPlayer_UnhandledException;});}}private void AudioPlayer_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e){if (System.Diagnostics.Debugger.IsAttached){System.Diagnostics.Debugger.Break();}}// 播放狀態(tài)發(fā)生改變時所調(diào)用的方法protected override void OnPlayStateChanged(BackgroundAudioPlayer player, AudioTrack track, PlayState playState){switch (playState){case PlayState.TrackReady:player.Play();break;case PlayState.TrackEnded:PlayNextTrack(player);break;case PlayState.Playing:break;case PlayState.Paused:break;case PlayState.Stopped:break;case PlayState.BufferingStarted:break;case PlayState.BufferingStopped:break;case PlayState.Rewinding:break;case PlayState.FastForwarding:break;case PlayState.Shutdown:break;case PlayState.Unknown:break;}NotifyComplete();}// 當程序改變播放行為時所調(diào)用的方法protected override void OnUserAction(BackgroundAudioPlayer player, AudioTrack track, UserAction action, object param){switch (action){case UserAction.Play:PlayTrack(player);break;case UserAction.SkipPrevious:PlayPreviousTrack(player);break;case UserAction.SkipNext:PlayNextTrack(player);break;case UserAction.Rewind:player.Rewind();break;case UserAction.FastForward:player.FastForward();break;case UserAction.Seek:player.Position = (TimeSpan)param;break;case UserAction.Pause:player.Pause();break;case UserAction.Stop:player.Stop();break;}NotifyComplete();}// 播放下一個 Trackprivate void PlayNextTrack(BackgroundAudioPlayer player){if (++_currentTrackNumber >= _playList.Count)_currentTrackNumber = 0;PlayTrack(player);}// 播放上一個 Trackprivate void PlayPreviousTrack(BackgroundAudioPlayer player){if (--_currentTrackNumber < 0)_currentTrackNumber = _playList.Count - 1;PlayTrack(player);}// 播放當前 Trackprivate void PlayTrack(BackgroundAudioPlayer player){player.Track = _playList[_currentTrackNumber];}// 出現(xiàn)異常時所調(diào)用的方法protected override void OnError(BackgroundAudioPlayer player, AudioTrack track, Exception error, bool isFatal){if (isFatal)Abort();elseNotifyComplete();}// 當后臺代理轉(zhuǎn)到休眠狀態(tài)或終止狀態(tài)前，系統(tǒng)會自動調(diào)用此方法，需要在 5 秒內(nèi)執(zhí)行完畢protected override void OnCancel(){}} }/** 主程序引用此項目后，會在 manifest 中添加如下信息：* <ExtendedTask Name="BackgroundTask">* <BackgroundServiceAgent Specifier="AudioPlayerAgent" Name="MyAudioPlayerAgent" Source="MyAudioPlayerAgent" Type="MyAudioPlayerAgent.AudioPlayer" />* </ExtendedTask>*/

2、前臺調(diào)用后臺代理播放音頻
BackgroundAudio.xaml

<phone:PhoneApplicationPage x:Class="Demo.Media.BackgroundAudio"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"xmlns:d="http://schemas.microsoft.com/expression/blend/2008"xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"FontFamily="{StaticResource PhoneFontFamilyNormal}"FontSize="{StaticResource PhoneFontSizeNormal}"Foreground="{StaticResource PhoneForegroundBrush}"SupportedOrientations="Portrait" Orientation="Portrait"mc:Ignorable="d" d:DesignHeight="768" d:DesignWidth="480"shell:SystemTray.IsVisible="True"><Grid x:Name="LayoutRoot" Background="Transparent"><StackPanel Orientation="Vertical"><Button x:Name="btnPrev" Content="上一首" Click="btnPrev_Click" /><Button x:Name="btnRewind" Content="快退" Click="btnRewind_Click" /><Button x:Name="btnPlay" Content="播放" Click="btnPlay_Click" /><Button x:Name="btnFastForward" Content="快進" Click="btnFastForward_Click" /><Button x:Name="btnNext" Content="下一首" Click="btnNext_Click" /><TextBlock x:Name="lblCurrentTrack" /><TextBlock x:Name="lblPosition" /></StackPanel></Grid></phone:PhoneApplicationPage>

BackgroundAudio.xaml.cs

/** 本例演示如何播放后臺音頻* * BackgroundAudioPlayer - 提供調(diào)用后臺播放音頻的相關(guān)功能* Instance - 返回 BackgroundAudioPlayer 實例* Track - 當前的 AudioTrack 對象。說明參見：MyAudioPlayerAgent/AudioPlayer.cs* PlayerState - 播放器狀態(tài)（Microsoft.Phone.BackgroundAudio.PlayState 枚舉）。說明參見：MyAudioPlayerAgent/AudioPlayer.cs* Position - 當前 AudioTrack 的播放位置* CanPause - 是否可暫停* CanSeek - 是否可以設(shè)置 Position 屬性* BufferingProgress - 緩沖百分比（0 - 1之間）* Volume - 音量（0 - 1之間，默認值為 0.85）。注：目前 wp 沒有提供 uvc（Universal Volume Control） 的接口* * Play - 播放當前 AudioTrack 的當前位置* Pause - 暫停* Stop - 停止* Rewind - 快退* FastForward - 快進 * SkipPrevious - 跳至上一個音頻* SkipNext - 跳至下一個音頻* Close - 關(guān)閉并釋放所有資源* * PlayStateChanged - PlayState 發(fā)生改變時所觸發(fā)的事件*/using System; using System.Collections.Generic; using System.Linq; using System.Net; using System.Windows; using System.Windows.Controls; using System.Windows.Documents; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Animation; using System.Windows.Shapes; using Microsoft.Phone.Controls;using Microsoft.Phone.BackgroundAudio; using System.Windows.Navigation; using System.IO.IsolatedStorage; using System.Windows.Resources;namespace Demo.Media {public partial class BackgroundAudio : PhoneApplicationPage{public BackgroundAudio(){InitializeComponent();Init();}protected override void OnNavigatedTo(NavigationEventArgs e){ProcessPlayState();}private void Init(){// 由于播放本地音頻時只能從獨立存儲中播放，所以此處把示例用音頻文件從程序包中復(fù)制到獨立存儲using (IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication()){if (!storage.FileExists("SuperMario.mp3")){StreamResourceInfo resource = Application.GetResourceStream(new Uri("Assets/SuperMario.mp3", UriKind.Relative));using (IsolatedStorageFileStream file = storage.CreateFile("SuperMario.mp3")){int chunkSize = 4096;byte[] bytes = new byte[chunkSize];int byteCount;while ((byteCount = resource.Stream.Read(bytes, 0, chunkSize)) > 0){file.Write(bytes, 0, byteCount);}}}}CompositionTarget.Rendering += new EventHandler(CompositionTarget_Rendering);BackgroundAudioPlayer.Instance.PlayStateChanged += new EventHandler(Instance_PlayStateChanged);}// 實時更新當前音頻播放的位置void CompositionTarget_Rendering(object sender, EventArgs e){if (BackgroundAudioPlayer.Instance != null)lblPosition.Text = BackgroundAudioPlayer.Instance.Position.TotalSeconds.ToString();}void Instance_PlayStateChanged(object sender, EventArgs e){ProcessPlayState();}void ProcessPlayState(){// 指定播放按鈕是顯示“播放”還是“暫停”switch (BackgroundAudioPlayer.Instance.PlayerState){case PlayState.Playing:btnPlay.Content = "暫停";break;case PlayState.Paused:case PlayState.Stopped:btnPlay.Content = "播放";break;}// 顯示音頻的 Title 和 Artistif (BackgroundAudioPlayer.Instance.Track != null)lblCurrentTrack.Text = BackgroundAudioPlayer.Instance.Track.Title + " by " + BackgroundAudioPlayer.Instance.Track.Artist;}// 播放或暫停音頻private void btnPlay_Click(object sender, RoutedEventArgs e){if (PlayState.Playing == BackgroundAudioPlayer.Instance.PlayerState){BackgroundAudioPlayer.Instance.Pause();}else{BackgroundAudioPlayer.Instance.Play();}}// 跳至下一首音頻private void btnNext_Click(object sender, RoutedEventArgs e){BackgroundAudioPlayer.Instance.SkipNext();}// 跳至上一首音頻private void btnPrev_Click(object sender, RoutedEventArgs e){BackgroundAudioPlayer.Instance.SkipPrevious();}// 快退private void btnRewind_Click(object sender, RoutedEventArgs e){if (PlayState.Playing == BackgroundAudioPlayer.Instance.PlayerState)BackgroundAudioPlayer.Instance.Rewind();}// 快進private void btnFastForward_Click(object sender, RoutedEventArgs e){if (PlayState.Playing == BackgroundAudioPlayer.Instance.PlayerState)BackgroundAudioPlayer.Instance.FastForward();}} }

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