更新 Windows Phone 后台音频代理中的歌曲标题？

Question

我正在为 windows phone 7.5 制作收音机应用程序。我想在后台播放收音机。为此，我正在使用 Windows Phone 后台音频代理。在代理代码中，我需要根据它指示轨道和所有信息。但我想更新曲目声明中的歌曲名称和艺术家姓名。曲目声明如下所示：

new AudioTrack(new Uri("Ring03.wma", UriKind.Relative), 
                        "Ringtone 3", 
                        "Windows Phone", 
                        "Windows Phone Ringtones", 
                        new Uri("shared/media/Ring03.jpg", UriKind.Relative)),

我想将字符串存储在一些变量中，然后用“Ringtone 3”替换它们。这样我就不断地改变标题字符串的值。我想每 5 秒更新一次标题。所以我希望我的媒体播放器向用户显示曲目信息，这样当用户更改音量时，他会在一个整洁的框中看到名称和艺术家。我试图做到这一点，但我得到了一个错误：（听起来像这样：

错误 4 字段初始化程序无法引用非静态字段、方法或属性 'MyAudioPlaybackAgent.AudioPlayer.title.get'

请帮忙：(

AudioPlayer.cs

using System;
using System.Windows;
using Microsoft.Phone.BackgroundAudio;

namespace AudioPlaybackAgent1
{
    public class AudioPlayer : AudioPlayerAgent
    {
        private static volatile bool _classInitialized;

        /// <remarks>
        /// AudioPlayer instances can share the same process. 
        /// Static fields can be used to share state between AudioPlayer instances
        /// or to communicate with the Audio Streaming agent.
        /// </remarks>
        public AudioPlayer()
        {
            if (!_classInitialized)
            {
                _classInitialized = true;
                // Subscribe to the managed exception handler
                Deployment.Current.Dispatcher.BeginInvoke(delegate
                {
                    Application.Current.UnhandledException += AudioPlayer_UnhandledException;
                });
            }
        }

        /// Code to execute on Unhandled Exceptions
        private void AudioPlayer_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
        {
            if (System.Diagnostics.Debugger.IsAttached)
            {
                // An unhandled exception has occurred; break into the debugger
                System.Diagnostics.Debugger.Break();
            }
        }

        /// <summary>
        /// Called when the playstate changes, except for the Error state (see OnError)
        /// </summary>
        /// <param name="player">The BackgroundAudioPlayer</param>
        /// <param name="track">The track playing at the time the playstate changed</param>
        /// <param name="playState">The new playstate of the player</param>
        /// <remarks>
        /// Play State changes cannot be cancelled. They are raised even if the application
        /// caused the state change itself, assuming the application has opted-in to the callback.
        /// 
        /// Notable playstate events: 
        /// (a) TrackEnded: invoked when the player has no current track. The agent can set the next track.
        /// (b) TrackReady: an audio track has been set and it is now ready for playack.
        /// 
        /// Call NotifyComplete() only once, after the agent request has been completed, including async callbacks.
        /// </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: Handle the shutdown state here (e.g. save state)
                    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>
        /// Called when the user requests an action using application/system provided UI
        /// </summary>
        /// <param name="player">The BackgroundAudioPlayer</param>
        /// <param name="track">The track playing at the time of the user action</param>
        /// <param name="action">The action the user has requested</param>
        /// <param name="param">The data associated with the requested action.
        /// In the current version this parameter is only for use with the Seek action,
        /// to indicate the requested position of an audio track</param>
        /// <remarks>
        /// User actions do not automatically make any changes in system state; the agent is responsible
        /// for carrying out the user actions if they are supported.
        /// 
        /// Call NotifyComplete() only once, after the agent request has been completed, including async callbacks.
        /// </remarks>
        protected override void OnUserAction(BackgroundAudioPlayer player, AudioTrack track, UserAction action, object param)
        {
            switch (action)
            {
                case UserAction.Play:
                    if (player.PlayerState != PlayState.Playing)
                    {
                        track.Title = "tracktitle";
                        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>
        /// Implements the logic to get the next AudioTrack instance.
        /// In a playlist, the source can be from a file, a web request, etc.
        /// </summary>
        /// <remarks>
        /// The AudioTrack URI determines the source, which can be:
        /// (a) Isolated-storage file (Relative URI, represents path in the isolated storage)
        /// (b) HTTP URL (absolute URI)
        /// (c) MediaStreamSource (null)
        /// </remarks>
        /// <returns>an instance of AudioTrack, or null if the playback is completed</returns>
        private AudioTrack GetNextTrack()
        {
            // TODO: add logic to get the next audio track

            AudioTrack track = null;

            // specify the track

            return track;
        }


        /// <summary>
        /// Implements the logic to get the previous AudioTrack instance.
        /// </summary>
        /// <remarks>
        /// The AudioTrack URI determines the source, which can be:
        /// (a) Isolated-storage file (Relative URI, represents path in the isolated storage)
        /// (b) HTTP URL (absolute URI)
        /// (c) MediaStreamSource (null)
        /// </remarks>
        /// <returns>an instance of AudioTrack, or null if previous track is not allowed</returns>
        private AudioTrack GetPreviousTrack()
        {
            // TODO: add logic to get the previous audio track

            AudioTrack track = null;

            // specify the track

            return track;
        }

        /// <summary>
        /// Called whenever there is an error with playback, such as an AudioTrack not downloading correctly
        /// </summary>
        /// <param name="player">The BackgroundAudioPlayer</param>
        /// <param name="track">The track that had the error</param>
        /// <param name="error">The error that occured</param>
        /// <param name="isFatal">If true, playback cannot continue and playback of the track will stop</param>
        /// <remarks>
        /// This method is not guaranteed to be called in all cases. For example, if the background agent 
        /// itself has an unhandled exception, it won't get called back to handle its own errors.
        /// </remarks>
        protected override void OnError(BackgroundAudioPlayer player, AudioTrack track, Exception error, bool isFatal)
        {
            if (isFatal)
            {
                Abort();
            }
            else
            {
                NotifyComplete();
            }

        }

        /// <summary>
        /// Called when the agent request is getting cancelled
        /// </summary>
        /// <remarks>
        /// Once the request is Cancelled, the agent gets 5 seconds to finish its work,
        /// by calling NotifyComplete()/Abort().
        /// </remarks>
        protected override void OnCancel()
        {

        }
    }
}

AudioStreamer.cs

using Microsoft.Phone.BackgroundAudio;
using System.Windows.Media;
namespace AudioStreamAgent1
{
    /// <summary>
    /// A background agent that performs per-track streaming for playback
    /// </summary>
    public class AudioTrackStreamer : AudioStreamingAgent
    {
        /// <summary>
        /// Called when a new track requires audio decoding
        /// (typically because it is about to start playing)
        /// </summary>
        /// <param name="track">
        /// The track that needs audio streaming
        /// </param>
        /// <param name="streamer">
        /// The AudioStreamer object to which a MediaStreamSource should be
        /// attached to commence playback
        /// </param>
        /// <remarks>
        /// To invoke this method for a track set the Source parameter of the AudioTrack to null
        /// before setting  into the Track property of the BackgroundAudioPlayer instance
        /// property set to true;
        /// otherwise it is assumed that the system will perform all streaming
        /// and decoding
        /// </remarks>
        protected override void OnBeginStreaming(AudioTrack track, AudioStreamer streamer)
        {
            //TODO: Set the SetSource property of streamer to a MSS source

            NotifyComplete();
        }

        /// <summary>
        /// Called when the agent request is getting cancelled
        /// The call to base.OnCancel() is necessary to release the background streaming resources
        /// </summary>
        protected override void OnCancel()
        {
            base.OnCancel();
        }
    }
}

Answer 1

后台音频代理不是广播流媒体的正确选择，您应该改用后台流媒体代理。 有一些很好的示例，其中包含大部分完整的音频流应用程序：Streaming MP3 player in WP7 和 Background audio overview for Windows Phone。

您可以通过此代码设置曲目名称：

  var player = BackgroundAudioPlayer.Instance;
  player.Track = "new track name";