学步园

　　有同学向我问这个问题，于是就Google了一下找到答案，不过是C下的，我将其改编成了C#的。

　　当设备被插入/拔出的时候，WINDOWS会向每个窗体发送WM_DEVICECHANGE 消息，当消息的wParam 值等于 DBT_DEVICEARRIVAL 时，表示Media设备被插入并且已经可用；如果wParam值等于DBT_DEVICEREMOVECOMPLETE，表示Media设备已经被移出。

它们的lParam都指向一个 DEV_BROADCAST_HDR结构体，其原形如下：

1 typedef struct _DEV_BROADCAST_HDR
2 {
3     DWORD dbch_size;
4     DWORD dbch_devicetype;
5     DWORD dbch_reserved;
6 } DEV_BROADCAST_HDR, *PDEV_BROADCAST_HDR;

这个结构体仅仅是一个“头”（HDR），其后还有附加数据，dbch_size表示结构体实例的字节数，当其中的dbch_devicetype字段值等于DBT_DEVTYP_VOLUME时，表示当前设备是逻辑驱动器，且lParam实际上指向的应该是DEV_BROADCAST_VOLUME 结构体实例（真佩服这种逻辑），DEV_BROADCAST_VOLUME 结构体原形如下：

1 typedef struct _DEV_BROADCAST_VOLUME {
2     DWORD dbcv_size;
3     DWORD dbcv_devicetype;
4     DWORD dbcv_reserved;
5     DWORD dbcv_unitmask;
6     WORD dbcv_flags;
7 } DEV_BROADCAST_VOLUME, *PDEV_BROADCAST_VOLUME;

其中dbcv_unitmask 字段表示当前改变的驱动器掩码，第一位表示驱动器号A，第二位表示驱动器号B，第三位表示驱动器号C，以此类推…… dbcv_flags 表示驱动器的类别，如果等于1，则是光盘驱动器；如果是2，则是网络驱动器；如果是硬盘、U盘则都等于0

　　所以，我只需要在程序中捕捉WM_DEVICECHANGE 消息，然后根据具体情况去处理即可，下面是我的测试代码：

using System;
using System.Runtime.InteropServices;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace UDiskDetect
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        [StructLayout(LayoutKind.Sequential)]
        struct DEV_BROADCAST_HDR
        {
            public UInt32 dbch_size;
            public UInt32 dbch_devicetype;
            public UInt32 dbch_reserved;
        }

        [StructLayout(LayoutKind.Sequential)]
        struct DEV_BROADCAST_VOLUME
        {
            public UInt32 dbcv_size;
            public UInt32 dbcv_devicetype;
            public UInt32 dbcv_reserved;
            public UInt32 dbcv_unitmask;
            public UInt16 dbcv_flags;
        }

        protected override void DefWndProc(ref Message m)
        {
            if (m.Msg == 0x0219)//WM_DEVICECHANGE
            {
                switch (m.WParam.ToInt32())
                {
                    case 0x8000://DBT_DEVICEARRIVAL
                        {
                            DEV_BROADCAST_HDR dbhdr = (DEV_BROADCAST_HDR)Marshal.PtrToStructure(m.LParam, typeof(DEV_BROADCAST_HDR));

                            if (dbhdr.dbch_devicetype == 0x00000002)//DBT_DEVTYP_VOLUME
                            {
                                DEV_BROADCAST_VOLUME dbv = (DEV_BROADCAST_VOLUME)Marshal.PtrToStructure(m.LParam, typeof(DEV_BROADCAST_VOLUME));
                                if (dbv.dbcv_flags == 0)
                                    AddVolumes(GetVolumes(dbv.dbcv_unitmask));
                            }
                            break;
                        }
                    case 0x8004://DBT_DEVICEREMOVECOMPLETE
                        {
                            DEV_BROADCAST_HDR dbhdr = (DEV_BROADCAST_HDR)Marshal.PtrToStructure(m.LParam, typeof(DEV_BROADCAST_HDR));

                            if (dbhdr.dbch_devicetype == 0x00000002)//DBT_DEVTYP_VOLUME
                            {
                                DEV_BROADCAST_VOLUME dbv = (DEV_BROADCAST_VOLUME)Marshal.PtrToStructure(m.LParam, typeof(DEV_BROADCAST_VOLUME));
                                if (dbv.dbcv_flags == 0)
                                    RemoveVolumes(GetVolumes(dbv.dbcv_unitmask));
                            }
                            break;
                        }
                }
            }
            base.DefWndProc(ref m);
        }

        /**//// <summary>
        /// 根据驱动器掩码返回驱动器号数组
        /// </summary>
        /// <param name="Mask">掩码</param>
        /// <returns>返回驱动器号数组</returns>
        public static char[] GetVolumes(UInt32 Mask)
        {
            List<char> Volumes = new List<char>();

            for (int i = 0; i < 32; i++)
            {
                uint p = (uint)Math.Pow(2, i);
                if ((p | Mask) == p)
                {
                    Volumes.Add((char)('A' + i));
                }
            }

            return Volumes.ToArray();
        }

        public void AddVolumes(char[] Volumes)
        {
            foreach (char volume in Volumes)
                listBox1.Items.Add(volume);
        }

        public void RemoveVolumes(char[] Volumes)
        {
            foreach (char volume in Volumes)
                listBox1.Items.Remove(volume);
        }

    }
}