函数|设计C#没有提供播放MP3等音频文件的类，要编写播放MP3等音频文件程序，必须使用第三方控件或类。本文使用API函数mciSendString，编写一个播放MP3等音频文件的类。 具体源码如下：
一、使用API函数mciSendString构成的媒体播放类。
using System;
using System.Runtime.InteropServices;
using System.Text;
using System.IO ;

namespace clsMCIPlay
{
/// <summary>
/// clsMci 的摘要说明。
/// </summary>
public class clsMCI
{
public clsMCI()
{
//
// TODO: 在此处添加构造函数逻辑
//
}

//定义API函数使用的字符串变量
[MarshalAs(UnmanagedType.ByValTStr,SizeConst=260)]
private string Name = "" ;
[MarshalAs(UnmanagedType.ByValTStr,SizeConst=128)]
private string durLength = "" ;
[MarshalAs(UnmanagedType.LPTStr,SizeConst=128)]
private string TemStr ="";
int ilong;
//定义播放状态枚举变量
public enum State
{
mPlaying = 1,
mPuase = 2,
mStop = 3
};
//结构变量
public struct structMCI
{
public bool bMut;
public int iDur;
public int iPos;
public int iVol;
public int iBal;
public string iName;
public State state;
};

public structMCI mc =new structMCI() ;

//取得播放文件属性
public string FileName
{
get
{
return mc.iName;
}

set
{
//ASCIIEncoding asc = new ASCIIEncoding();
try
{
TemStr ="";
TemStr = TemStr.PadLeft(127,Convert.ToChar(" "));
Name = Name.PadLeft(260,Convert.ToChar(" ")) ;
mc.iName = value;
ilong = APIClass.GetShortPathName(mc.iName,Name, Name.Length);
Name = GetCurrPath(Name);
//Name = "open " + Convert.ToChar(34) + Name + Convert.ToChar(34) + " alias media";
Name = "open " + Convert.ToChar(34) + Name + Convert.ToChar(34) + " alias media";
ilong = APIClass.mciSendString("close all", TemStr, TemStr.Length , 0);
ilong = APIClass.mciSendString( Name, TemStr, TemStr.Length, 0);
ilong = APIClass.mciSendString("set media time format milliseconds", TemStr, TemStr.Length , 0);
mc.state = State.mStop;
}
catch
{
MessageBox.Show("出错错误!");
}
}
}
//播放
public void play()
{
TemStr = "";
TemStr = TemStr.PadLeft(127,Convert.ToChar(" "));
APIClass.mciSendString("play media", TemStr, TemStr.Length , 0);
mc.state = State.mPlaying ;
}
//停止
public void StopT()
{
TemStr = "";
TemStr = TemStr.PadLeft(128,Convert.ToChar(" "));
ilong = APIClass.mciSendString("close media", TemStr, 128, 0);
ilong = APIClass.mciSendString("close all", TemStr, 128, 0);
mc.state = State.mStop ;

}

public void Puase()
{
TemStr = "";
TemStr = TemStr.PadLeft(128,Convert.ToChar(" "));
ilong = APIClass.mciSendString("pause media", TemStr, TemStr.Length, 0);
mc.state = State.mPuase ;
}
private string GetCurrPath(string name)
{
if(name.Length <1) return "";
name = name.Trim();
name = name.Substring(0,name.Length-1);
return name;
}
//总时间
public int Duration
{
get
{
durLength = "";
durLength = durLength.PadLeft(128,Convert.ToChar(" ")) ;
APIClass.mciSendString("status media length", durLength, durLength.Length, 0);
durLength = durLength.Trim();
if(durLength == "") return 0;
return (int)(Convert.ToDouble(durLength) / 1000f);
}
}

//当前时间
public int CurrentPosition
{
get
{
durLength = "";
durLength = durLength.PadLeft(128,Convert.ToChar(" ")) ;
APIClass.mciSendString("status media position", durLength, durLength.Length, 0);
mc.iPos = (int)(Convert.ToDouble(durLength) / 1000f);
return mc.iPos;
}
}



}

public class APIClass
{

[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
public static extern int GetShortPathName (
string lpszLongPath,
string shortFile,
int cchBuffer
);

[DllImport("winmm.dll", EntryPoint="mciSendString", CharSet = CharSet.Auto)]
public static extern int mciSendString (
string lpstrCommand,
string lpstrReturnString,
int uReturnLength,
int hwndCallback
);

}

}

二、用于测试媒体播放类的简单代码：
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Runtime.InteropServices;
using System.Text;
using System.IO ;
using clsMCIPlay;

namespace MCIPlay
{
/// <summary>
/// Form1 的摘要说明。
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
private System.ComponentModel.IContainer components;
private System.Windows.Forms.Timer timer1;
private System.Windows.Forms.Button Play;
private System.Windows.Forms.Button Stop;
private System.Windows.Forms.Button Puase;
private System.Windows.Forms.Label PlayFileName;
private System.Windows.Forms.Label Duration;
private System.Windows.Forms.Label CurrentPosition;
private System.Windows.Forms.OpenFileDialog openFileDialog1;
private System.Windows.Forms.Button BrowserFile;
clsMCI mp = new clsMCI();


public Form1()
{
//
// Windows 窗体设计器支持所必需的
//
InitializeComponent();

//
// TODO: 在 InitializeComponent 调用后添加任何构造函数代码
//
}

/// <summary>
/// 清理所有正在使用的资源。
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows 窗体设计器生成的代码
/// <summary>
/// 设计器支持所需的方法 - 不要使用代码编辑器修改
/// 此方法的内容。
/// </summary>
private void InitializeComponent()
{
this.components = new System.ComponentModel.Container();
this.Play = new System.Windows.Forms.Button();
this.PlayFileName = new System.Windows.Forms.Label();
this.Duration = new System.Windows.Forms.Label();
this.Stop = new System.Windows.Forms.Button();
this.Puase = new System.Windows.Forms.Button();
this.CurrentPosition = new System.Windows.Forms.Label();
this.timer1 = new System.Windows.Forms.Timer(this.components);
this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();
this.BrowserFile = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// Play
//
this.Play.Location = new System.Drawing.Point(102, 243);
this.Play.Name = "Play";
this.Play.Size = new System.Drawing.Size(78, 24);
this.Play.TabIndex = 0;
this.Play.Text = "Play";
this.Play.Click += new System.EventHandler(this.Play_Click);
//
// PlayFileName
//
this.PlayFileName.AutoSize = true;
this.PlayFileName.Location = new System.Drawing.Point(12, 15);
this.PlayFileName.Name = "PlayFileName";
this.PlayFileName.Size = new System.Drawing.Size(0, 17);
this.PlayFileName.TabIndex = 1;
//
// Duration
//
this.Duration.AutoSize = true;
this.Duration.Location = new System.Drawing.Point(15, 51);
this.Duration.Name = "Duration";
this.Duration.Size = new System.Drawing.Size(0, 17);
this.Duration.TabIndex = 2;
//
// Stop
//
this.Stop.Location = new System.Drawing.Point(282, 243);
this.Stop.Name = "Stop";
this.Stop.Size = new System.Drawing.Size(81, 24);
this.Stop.TabIndex = 3;
this.Stop.Text = "Stop";
this.Stop.Click += new System.EventHandler(this.Stop_Click);
//
// Puase
//
this.Puase.Location = new System.Drawing.Point(198, 243);
this.Puase.Name = "Puase";
this.Puase.Size = new System.Drawing.Size(72, 24);
this.Puase.TabIndex = 4;
this.Puase.Text = "Puase";
this.Puase.Click += new System.EventHandler(this.Puase_Click);
//
// CurrentPosition
//
this.CurrentPosition.AutoSize = true;
this.CurrentPosition.Location = new System.Drawing.Point(15, 87);
this.CurrentPosition.Name = "CurrentPosition";
this.CurrentPosition.Size = new System.Drawing.Size(0, 17);
this.CurrentPosition.TabIndex = 5;
//
// timer1
//
this.timer1.Enabled = true;
this.timer1.Interval = 1000;
this.timer1.Tick += new System.EventHandler(this.timer1_Tick);
//
// BrowserFile
//
this.BrowserFile.Location = new System.Drawing.Point(312, 165);
this.BrowserFile.Name = "BrowserFile";
this.BrowserFile.Size = new System.Drawing.Size(87, 24);
this.BrowserFile.TabIndex = 6;
this.BrowserFile.Text = "SelectFile";
this.BrowserFile.Click += new System.EventHandler(this.BrowserFile_Click);
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
this.ClientSize = new System.Drawing.Size(433, 287);
this.Controls.Add(this.BrowserFile);
this.Controls.Add(this.CurrentPosition);
this.Controls.Add(this.Puase);
this.Controls.Add(this.Stop);
this.Controls.Add(this.Duration);
this.Controls.Add(this.PlayFileName);
this.Controls.Add(this.Play);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);

}
#endregion

/// <summary>
/// 应用程序的主入口点。
/// </summary>
[STAThread]
static void Main()
{
Application.Run(new Form1());
}

//选择MP3文件播放
private void Play_Click(object sender, System.EventArgs e)
{
try
{
mp.play();
}
catch
{
MessageBox.Show("出错错误!");
}
}

//暂停播放
private void Puase_Click(object sender, System.EventArgs e)
{
try
{
mp.Puase();
}
catch
{
MessageBox.Show("出错错误!");
}

}

//停止播放
private void Stop_Click(object sender, System.EventArgs e)
{
try
{
mp.StopT();
}
catch
{
MessageBox.Show("出错错误!");
}
}

//每秒显示一次播放进度
private void timer1_Tick(object sender, System.EventArgs e)
{
CurrentPosition.Text = mp.CurrentPosition.ToString();
}

//浏览文件
private void BrowserFile_Click(object sender, System.EventArgs e)
{
try
{
openFileDialog1.Filter = "*.mp3|*.mp3";
openFileDialog1.FileName = "";
if(openFileDialog1.ShowDialog() == DialogResult.OK)
{
mp.FileName = openFileDialog1.FileName ;
PlayFileName.Text = openFileDialog1.FileName ;
Duration.Text = mp.Duration.ToString() ;
}
}
catch
{
MessageBox.Show("出错错误!");
}
}

}

}