重新想象 Windows 8 Store Apps (65) - 后台任务: 音乐的后台播放和控制
重新想象 Windows 8 Store Apps (65) - 后台任务: 音乐的后台播放和控制
作者：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
<Page x: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
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