Winows Phone 7 不温不火学习之《音乐播放示例》

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.Xna.Framework;
using  Microsoft.Xna.Framework.Media;
using  System.Windows.Threading;
using  System.IO;
using  System.Windows.Resources;
using  System.Windows.Media.Imaging;


namespace  PostCodeManager
{
     public   partial   class  MainPage : PhoneApplicationPage
    {
         #region  成员声明
        Song _playSong;  // 声明一个Song 类型的变量
         bool  _historyItemLaunch;
         const  String _playSongKey  =   " playSong " ;
         #endregion


         //  Constructor
         public  MainPage()
        {
            InitializeComponent();
            _playSong  =   null ;
            _historyItemLaunch  =   false ;

             // 声明一个Timer 使用线程运行 XNA internals 来自于微软XNA框架
            DispatcherTimer dt  =   new  DispatcherTimer();
            dt.Interval  =  TimeSpan.FromMilliseconds( 33 );
             // 使用委托调用逐帧调用  FrameworkDispatcher.Update();
            dt.Tick  +=   delegate
            {
                 try
                {
                     //  这个函数作用是更新各种XNA组件状态，并触发相应的事件,这个是必须的，否则会报异常
                    FrameworkDispatcher.Update();
                   
                }
                 catch   
                {
                    
                     throw ;
                }
            };
            dt.Start();

            MediaPlayer.MediaStateChanged  +=   new  EventHandler < EventArgs > (MediaPlayer_MediaStateChanged);
           
        }

         ///   <summary>
         ///  当页面进入时调用 
         ///   </summary>
         ///   <param name="e"></param>
         protected   override   void  OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
        {
            MediaLibrary library  =   new  MediaLibrary();
             if  (NavigationContext.QueryString.ContainsKey(_playSongKey))
            {
                String songToPlay  =  NavigationContext.QueryString[_playSongKey];
                 foreach  (Song song  in  library.Songs)
                {
                     if  ( 0 == String.Compare(songToPlay,song.Name))
                    {
                        _playSong  =  song;
                    }
                }
                _historyItemLaunch  =   true ;
            }
             else   if  (MediaPlayer.State == MediaState.Playing)
            {
                _playSong  =  MediaPlayer.Queue.ActiveSong;
            }
             else
            {
                Random rd  =   new  Random();
                 if  (library.Songs.Count > 0 )
                {
                    _playSong  =  library.Songs[rd.Next(library.Songs.Count)];
                }
                 else
                {
                    SongName.Text  =   " no songs in library " ;
                    btn_play_music.IsEnabled  =   false ;
                }
            }


             base .OnNavigatedTo(e);
        }

         void  MediaPlayer_MediaStateChanged( object  sender, EventArgs e)
        {
             switch  (MediaPlayer.State)
            {
                
                 case  MediaState.Playing:
                    btn_play_music.IsEnabled  =   false ;
                    btn_stop.IsEnabled  =   true ;
                     break ;
                 case  MediaState.Paused: 
                 case  MediaState.Stopped:
                    btn_play_music.IsEnabled  =   true ;
                    btn_stop.IsEnabled  =   false ;
                     break ; 
            }
        }

         ///   <summary>
         ///  为主窗体添加UI加载完成后的事件
         ///   </summary>
         ///   <param name="sender"></param>
         ///   <param name="e"></param>
         private   void  PhoneApplicationPage_Loaded( object  sender, RoutedEventArgs e)
        {
            PopulateSongMetaData();
            setInitialButtonState();
             if  (_historyItemLaunch)
            {
                playSong();
            }
        }
        

         ///   <summary>
         ///  开始播放音乐 
         ///   </summary>
         ///   <param name="sender"></param>
         ///   <param name="e"></param>
         private   void  btn_play_music_Click( object  sender, RoutedEventArgs e)
        {
            playSong();
        }

         ///   <summary>
         ///  停止播放音乐
         ///   </summary>
         ///   <param name="sender"></param>
         ///   <param name="e"></param>
         private   void  btn_stop_Click( object  sender, RoutedEventArgs e)
        {
            stopSong();
        }

         ///   <summary>
         ///  播放
         ///   </summary>
         private   void  playSong()
        {
             if  (_playSong != null )
            {
                MediaPlayer.Play(_playSong);
            }
        }
         ///   <summary>
         ///  停止
         ///   </summary>
         private   void  stopSong()
        {
             if  (MediaState.Playing == MediaPlayer.State)
            {
                MediaPlayer.Stop();
            }
        }

         ///   <summary>
         ///  使用图片读取图片封面
         ///   </summary>
         private   void  PopulateSongMetaData() 
        {
             if  (_playSong != null )
            {
                SongName.Text  =  _playSong.Name;
                Stream albumArtStream  =  _playSong.Album.GetAlbumArt();
                 if  (albumArtStream == null )
                {
                    StreamResourceInfo albumArtPlaceholder  =  Application.GetResourceStream( new  Uri( " ApplicationIcon.png " , UriKind.Relative));
                    albumArtStream  =  albumArtPlaceholder.Stream;
                }
                BitmapImage albumArtImage  =   new  BitmapImage();
                albumArtImage.SetSource(albumArtStream);
                cover.Source  =  albumArtImage;
            }
        }

         ///   <summary>
         ///  初始化按钮 
         ///   </summary>
         private   void  setInitialButtonState() 
        {
             switch  (MediaPlayer.State)
            {

                 case  MediaState.Playing:
                    btn_play_music.IsEnabled  =   false ;
                    btn_stop.IsEnabled  =   true ;
                     break ;
                 case  MediaState.Paused:
                 case  MediaState.Stopped:
                    btn_play_music.IsEnabled  =   true ;
                    btn_stop.IsEnabled  =   false ;
                     break ;
            }
        }

         
         
    }
}