// usb消息定义
public const int WM_DEVICE_CHANGE = 0x219;
public const int DBT_DEVICEARRIVAL = 0x8000;
public const int DBT_DEVICE_REMOVE_COMPLETE = 0x8004;
public const UInt32 DBT_DEVTYP_PORT = 0x00000003;

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

[StructLayout(LayoutKind.Sequential)]
protected struct DEV_BROADCAST_PORT_Fixed
{
public uint dbcp_size;
public uint dbcp_devicetype;
public uint dbcp_reserved;
// Variable?length field dbcp_name is declared here in the C header file.
}

/// <summary>
/// 检测USB串口的拔插
/// </summary>
/// <param name="m"></param>
protected override void WndProc(ref Message m)
{
if (m.Msg == WM_DEVICE_CHANGE) // 捕获USB设备的拔出消息WM_DEVICECHANGE
{
switch (m.WParam.ToInt32())
{
case DBT_DEVICE_REMOVE_COMPLETE: // USB拔出 
DEV_BROADCAST_HDR dbhd = (DEV_BROADCAST_HDR)Marshal.PtrToStructure(m.LParam, typeof(DEV_BROADCAST_HDR));
if (dbhd.dbch_devicetype == DBT_DEVTYP_PORT)
{
string portName = Marshal.PtrToStringUni((IntPtr)(m.LParam.ToInt32() + Marshal.SizeOf(typeof(DEV_BROADCAST_PORT_Fixed))));

if (cbPort.Items.Contains(portName))
{
cbPort.Items.Remove(portName);
}
if (wr != null)
{
wr.Close();
}
}

break;
case DBT_DEVICEARRIVAL: // USB插入获取对应串口名称
DEV_BROADCAST_HDR dbhdr = (DEV_BROADCAST_HDR)Marshal.PtrToStructure(m.LParam, typeof(DEV_BROADCAST_HDR));
if (dbhdr.dbch_devicetype == DBT_DEVTYP_PORT)
{
string portName = Marshal.PtrToStringUni((IntPtr)(m.LParam.ToInt32() + Marshal.SizeOf(typeof(DEV_BROADCAST_PORT_Fixed))));

if (!cbPort.Items.Contains(portName))
{
cbPort.Items.Add(portName);
}
}
break;
}
}
base.WndProc(ref m);
}