Windows 8 Store Apps学习（65） 后台任务: 音乐的后台播放和控制2014-09-02 cnblogs webabcd介绍重新想象 Windows 8 Store Apps 之 后台任务音乐的后台播放和控制示例用于保存每首音乐的相关信息的对象BackgroundTask/SongModel.cs
/* * 用于保存每首音乐的相关信息 */using System;using System.Threading.Tasks;using Windows.Storage;namespace XamlDemo.BackgroundTask{public class SongModel{/// <summary>/// 音乐文件/// </summary>public StorageFile File;/// <summary>/// 艺术家/// </summary>public string Artist;/// <summary>/// 音乐名称/// </summary>public string Title;public SongModel（StorageFile file）{File = file;}/// <summary>/// 加载音乐的相关属性/// </summary>public async Task LoadMusicPropertiesAsync（）{var properties = await this.File.Properties.GetMusicPropertiesAsync（）;Artist = properties.Artist;Title = properties.Title;}}}演示如何通过 MediaControl 实现音乐的后台播放和控制BackgroundTask/MediaControlDemo.xaml
<Pagex:Class="XamlDemo.BackgroundTask.MediaControlDemo"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"><TextBlock Name="lblMsg" FontSize="14.667"/><Button Name="btnSelectFiles" Content="Select Files" Click="btnSelectFiles_Click" Margin="0 10 0 0"/><Button Name="btnPlay" Content="Play" Click="btnPlay_Click" Margin="0 10 0 0"/><！--为了使音乐可以后台播放，需要将 MediaElement 的 AudioCategory 属性设置为 BackgroundCapableMedia--><MediaElement Name="mediaElement" AudioCategory="BackgroundCapableMedia" AutoPlay="False"MediaOpened="mediaElement_MediaOpened" MediaEnded="mediaElement_MediaEnded" CurrentStateChanged="mediaElement_CurrentStateChanged"/></StackPanel></Grid></Page>
BackgroundTask/MediaControlDemo.cs
/* * 演示如何通过 MediaControl 实现音乐的后台播放和控制 ** 注： * 1、需要在 Package.appxmanifest 中增加后台任务声明，并勾选“音频” * 2、需要将 MediaElement 的 AudioCategory 属性设置为 BackgroundCapableMedia ** 另： * 按下平板上的音量键或者多媒体键盘上的相关按键，会弹出后台音频的控制框，通过 MediaControl 来监听用户在此音频控制框上的操作 */using System;using System.Collections.Generic;using System.Threading.Tasks;using Windows.Media;using Windows.Storage;using Windows.Storage.Pickers;using Windows.Storage.Streams;using Windows.UI.Core;using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;using Windows.UI.Xaml.Media;namespace XamlDemo.BackgroundTask{public sealed partial class MediaControlDemo : Page{private List<SongModel> _playList = new List<SongModel>（）; // 后台需要播放的音乐列表private int _currentSongIndex = 0; // 当前播放的音乐private bool _previousTrackPressedRegistered = false; // MediaControl 是否注册了 PreviousTrackPressed 事件private bool _nextTrackPressedRegistered = false; // MediaControl 是否注册了 NextTrackPressed 事件public MediaControlDemo（）{this.InitializeComponent（）;MediaControl.PlayPauseTogglePressed += MediaControl_PlayPauseTogglePressed; // 按下了 play/pause 键MediaControl.PlayPressed += MediaControl_PlayPressed; // 按下了 play 键MediaControl.PausePressed += MediaControl_PausePressed; // 按下了 pause 键MediaControl.StopPressed += MediaControl_StopPressed; // 按下了 stop 键MediaControl.PreviousTrackPressed += MediaControl_PreviousTrackPressed; // 按下了“上一首”键MediaControl.NextTrackPressed += MediaControl_NextTrackPressed; // 按下了“下一首”键MediaControl.RewindPressed += MediaControl_RewindPressed; // 按下了“快退”键MediaControl.FastForwardPressed += MediaControl_FastForwardPressed; // 按下了“快进”键MediaControl.SoundLevelChanged += MediaControl_SoundLevelChanged; // 音量级别发生了改变// MediaControl.RecordPressed += MediaControl_RecordPressed;// MediaControl.ChannelDownPressed += MediaControl_ChannelDownPressed;// MediaControl.ChannelUpPressed += MediaControl_ChannelUpPressed;// MediaControl.ArtistName; // 当前播放的音乐的艺术家// MediaControl.TrackName; // 当前播放的音乐的名称// MediaControl.AlbumArt; // 当前播放的音乐的专辑封面的路径// MediaControl.IsPlaying; // 当前音乐是否正在播放// MediaControl.SoundLevel; // 当前播放的音乐的音量级别（Muted, Low, Full） _previousTrackPressedRegistered = true; _nextTrackPressedRegistered = true;}// 按下了音频控制框上的 play/pause 键async void MediaControl_PlayPauseTogglePressed（object sender, object e）{if （MediaControl.IsPlaying）{await Dispatcher.RunAsync（CoreDispatcherPriority.Normal, （） =>{mediaElement.Pause（）;}）;await OutputMessage（"Play/Pause Pressed - Pause"）;}else{await Dispatcher.RunAsync（CoreDispatcherPriority.Normal, （） =>{mediaElement.Play（）;}）;await OutputMessage（"Play/Pause Pressed - Play"）;}}// 按下了音频控制框上的 play 键async void MediaControl_PlayPressed（object sender, object e）{await Dispatcher.RunAsync（CoreDispatcherPriority.Normal, （） =>{mediaElement.Play（）;}）;await OutputMessage（"Play Pressed"）;}// 按下了音频控制框上的 pause 键async void MediaControl_PausePressed（object sender, object e）{await Dispatcher.RunAsync（Windows.UI.Core.CoreDispatcherPriority.Normal, （） =>{mediaElement.Pause（）;}）;await OutputMessage（"Pause Pressed"）;}// 按下了音频控制框上的 stop 键async void MediaControl_StopPressed（object sender, object e）{await Dispatcher.RunAsync（Windows.UI.Core.CoreDispatcherPriority.Normal, （） =>{mediaElement.Stop（）;}）;await OutputMessage（"Stop Pressed"）;}// 按下了音频控制框上的“上一首”键async void MediaControl_PreviousTrackPressed（object sender, object e）{await OutputMessage（"Previous Track Pressed"）;if （_currentSongIndex > 0）{if （_currentSongIndex == （_playList.Count - 1））{if （！_nextTrackPressedRegistered）{MediaControl.NextTrackPressed += MediaControl_NextTrackPressed;_nextTrackPressedRegistered = true;}}_currentSongIndex--;if （_currentSongIndex == 0）{MediaControl.PreviousTrackPressed -= MediaControl_PreviousTrackPressed;_nextTrackPressedRegistered = false;}await SetCurrentPlayingAsync（_currentSongIndex）;}}// 按下了音频控制框上的“下一首”键async void MediaControl_NextTrackPressed（object sender, object e）{await OutputMessage（"Next Track Pressed"）;if （_currentSongIndex < （_playList.Count - 1））{_currentSongIndex++;await SetCurrentPlayingAsync（_currentSongIndex）;if （_currentSongIndex > 0）{if （！_previousTrackPressedRegistered）{MediaControl.PreviousTrackPressed += MediaControl_PreviousTrackPressed;_previousTrackPressedRegistered = true;}}if （_currentSongIndex == （_playList.Count - 1））{if （_nextTrackPressedRegistered）{MediaControl.NextTrackPressed -= MediaControl_NextTrackPressed;_nextTrackPressedRegistered = false;}}}}// 按下了音频控制框上的“快退”键，即长按“上一首”键async void MediaControl_RewindPressed（object sender, object e）{await OutputMessage（"Rewind Pressed"）;}// 按下了音频控制框上的“快进”键，即长按“下一首”键async void MediaControl_FastForwardPressed（object sender, object e）{await OutputMessage（"Fast Forward Pressed"）;}// 音量级别发生变化时（Muted, Low, Full）async void MediaControl_SoundLevelChanged（object sender, object e）{await OutputMessage（"Sound Level Changed"）;}// 创建一个需要在后台播放的音乐列表private async void btnSelectFiles_Click（object sender, RoutedEventArgs e）{FileOpenPicker openPicker = new FileOpenPicker（）;openPicker.ViewMode = PickerViewMode.List;openPicker.SuggestedStartLocation = PickerLocationId.MusicLibrary;openPicker.FileTypeFilter.Add（".mp3"）;openPicker.FileTypeFilter.Add（".wma"）;IReadOnlyList<StorageFile> files = await openPicker.PickMultipleFilesAsync（）;if （files.Count > 0）{await CreatePlaylist（files）;await SetCurrentPlayingAsync（_currentSongIndex）;}}// 开始播放private async void btnPlay_Click（object sender, RoutedEventArgs e）{if （MediaControl.IsPlaying）{await Dispatcher.RunAsync（CoreDispatcherPriority.Normal, （） =>{mediaElement.Pause（）;}）;await OutputMessage（"Play/Pause Pressed - Pause"）;}else{await Dispatcher.RunAsync（CoreDispatcherPriority.Normal, （） =>{mediaElement.Play（）;}）;await OutputMessage（"Play/Pause Pressed - Play"）;}}// MediaElement 打开文件后，如果需要播放则立刻播放private void mediaElement_MediaOpened（object sender, RoutedEventArgs e）{if （MediaControl.IsPlaying）{mediaElement.Play（）;}}// 当前音乐播放完后，转到下一首private async void mediaElement_MediaEnded（object sender, RoutedEventArgs e）{if （_currentSongIndex < _playList.Count - 1）{_currentSongIndex++;await SetCurrentPlayingAsync（_currentSongIndex）;if （MediaControl.IsPlaying）{mediaElement.Play（）;}}}// 根据前台的操作，设置 MediaControl 的 IsPlaying 属性// private void mediaElement_CurrentStateChanged（object sender, RoutedEventArgs e）{if （mediaElement.CurrentState == MediaElementState.Playing）{MediaControl.IsPlaying = true;btnPlay.Content = "Pause";}else{MediaControl.IsPlaying = false;btnPlay.Content = "Play";}}// 创建音乐列表private async Task CreatePlaylist（IReadOnlyList<StorageFile> files）{if （_previousTrackPressedRegistered）{MediaControl.PreviousTrackPressed -= MediaControl_PreviousTrackPressed;_previousTrackPressedRegistered = false;}if （_nextTrackPressedRegistered）{MediaControl.NextTrackPressed -= MediaControl_NextTrackPressed;_nextTrackPressedRegistered = false;}_playList.Clear（）;_currentSongIndex = 0;if （files.Count > 0）{if （files.Count > 1）{MediaControl.NextTrackPressed += MediaControl_NextTrackPressed;_nextTrackPressedRegistered = true;}foreach （StorageFile file in files）{SongModel song = new SongModel（file）;await song.LoadMusicPropertiesAsync（）;_playList.Add（song）;}}}// 指定当前需要播放的音乐private async Task SetCurrentPlayingAsync（int playListIndex）{string errorMessage = null;IRandomAccessStream stream = null;try{stream = await _playList[playListIndex].File.OpenAsync（Windows.Storage.FileAccessMode.Read）;await Dispatcher.RunAsync（CoreDispatcherPriority.Normal, （） => {mediaElement.SetSource（stream, _playList[playListIndex].File.ContentType）; }）;}catch （Exception e）{errorMessage = e.Message;}if （errorMessage ！= null）{await OutputMessage（errorMessage）;}MediaControl.ArtistName = _playList[playListIndex].Artist;MediaControl.TrackName = _playList[playListIndex].Title;}// 输出信息private async Task OutputMessage（string message）{await Dispatcher.RunAsync（CoreDispatcherPriority.Normal, （） =>{lblMsg.Text = message + ": " + DateTime.Now.ToString（"yyyy-MM-dd hh:mm:ss"）;}）;}}}OK源码下载：http://files.cnblogs.com/webabcd/Windows8.rar
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