在C#.Net中播放MIDI文件时听不到声音

Question

我使用此代码为我的游戏播放MIDI文件，但我听不到任何声音从我的扬声器。你能帮我吗？我有急事，麻烦你...我的扬声器已打开;)

[DllImport("winmm.dll", EntryPoint="mciSendStringA")]
private static extern long mciSendString(string lpstrCommand, string lpstrReturnString, long uReturnLength, long hwndCallback);
public static long PlayMidiFile(string MidiFile)
{
 long lRet = -1;

 if (File.Exists(MidiFile)) 
 {
  lRet = mciSendString("stop midi", "", 0, 0);
  lRet = mciSendString("close midi", "", 0, 0);
  lRet = mciSendString(("open sequencer!" 
   + (MidiFile + " alias midi")), "", 0, 0);
  lRet = mciSendString("play midi", "", 0, 0);
  return lRet;
 }

 else
 {
  //Error Message
  return lRet;
 }
}

Answer 1

我对你的winmm.dll实现不是很确定，但是我有一个经过测试并且可以正常工作的代码。

我从这个开源项目中获得了源代码：Tea Timer。

代码的实现非常简单，如下所示。希望能有所帮助。

using System;
using System.Text;
using System.Runtime.InteropServices;
using System.IO;

namespace TeaTimer
{
    /// <summary>
    /// MCIPlayer is based off code by Slain.
    /// Found here: http://www.sadeveloper.net/Articles_View.aspx?articleID=212
    /// </summary>
    public class MCIPlayer
    {
        private static readonly string sAlias="TeaTimerAudio";

        [DllImport("winmm.dll")]
        private static extern long mciSendString(string strCommand,StringBuilder strReturn,int iReturnLength, IntPtr hwndCallback);
        [DllImport("Winmm.dll")]
        private static extern long PlaySound(byte[] data, IntPtr hMod, UInt32 dwFlags);

        public static void Play(string sFile)
        {
            _Open(sFile);
            _Play();
        }
        public static void Stop() 
        {
            _Close();
        }

        private static void _Open(string sFileName)
        {
            if(_Status()!="")
                _Close();

            string sCommand = "open \"" + sFileName + "\" alias "+sAlias;
            mciSendString(sCommand, null, 0, IntPtr.Zero);
        }

        private static void _Close()
        {
            string sCommand = "close "+sAlias;
            mciSendString(sCommand, null, 0, IntPtr.Zero);
        }

        private static void _Play()
        {
            string sCommand = "play "+sAlias;
            mciSendString(sCommand, null, 0, IntPtr.Zero);
        }

        private static string _Status()
        {
            StringBuilder sBuffer = new StringBuilder(128);
            mciSendString("status "+sAlias+" mode", sBuffer, sBuffer.Capacity, IntPtr.Zero);
            return sBuffer.ToString();
        }
    }
}

编辑:这是播放和停止音乐文件的方式：

public static void playSound(string sFile) 
{
    //WavPlay.WavPlayer.Play(sFile);
    MCIPlayer.Play(sFile);
}
public static void stopSound() 
{
    //WavPlay.WavPlayer.StopPlay();
    MCIPlayer.Stop();
}

Answer 2

我以前用的定义是...

[DllImport("winmm.dll", EntryPoint = "mciSendStringA")] 

public static extern void mciSendStringA(string lpstrCommand, string lpstrReturnString, long uReturnLength, long hwndCallback); 

...in .Net 3.5但在.Net 4.0中给了我和不平衡的pinvoke异常！我用这个解决了这个问题...

[DllImport("winmm.dll", EntryPoint = "mciSendStringA")]

public static extern void mciSendStringA(string lpstrCommand, string lpstrReturnString, int uReturnLength, IntPtr hwndCallback); 

...and将IntPtr.Zero作为最后一个参数传入。

唯一的区别是uReturnLength是一个int (而不是long)，而hwndCallback是一个IntPtr (而不是long)。

希望这能帮到你。