这个东西如何用

这个东西怎么用啊
Unit   USBUnit;
Interface
Uses
    Windows,   SysUtils,   Classes,   Messages,   Forms;
Type
    PDevBroadcastHdr   =   ^DEV_BROADCAST_HDR;
    DEV_BROADCAST_HDR   =   Packed   Record
        dbch_size:   DWORD;
        dbch_devicetype:   DWORD;
        dbch_reserved:   DWORD;
    End;
    PDevBroadcastDeviceInterface   =   ^DEV_BROADCAST_DEVICEINTERFACE;
    DEV_BROADCAST_DEVICEINTERFACE   =   Record
        dbcc_size:   DWORD;
        dbcc_devicetype:   DWORD;
        dbcc_reserved:   DWORD;
        dbcc_classguid:   TGUID;
        dbcc_name:   short;
    End;
    TUSB   =   Class(TObject)
    private
        FWindowHandle:   HWND;
        FOnUSBArrival:   TNotifyEvent;
        FOnUSBRemove:   TNotifyEvent;
        Procedure   WndProc(Var   Msg:   TMessage);
        Function   USBRegister:   Boolean;
    protected
        Procedure   WMDeviceChange(Var   Msg:   TMessage);   dynamic;
    public
        Constructor   Create;
        Destructor   Destroy;   override;
        Property   OnUSBArrival:   TNotifyEvent   read   FOnUSBArrival   write   FOnUSBArrival;
        Property   OnUSBRemove:   TNotifyEvent   read   FOnUSBRemove   write   FOnUSBRemove;
    End;
Const
    GUID_DEVINTERFACE_USB_DEVICE:   TGUID   =   '{A5DCBF10-6530-11D2-901F-00C04FB951ED} ';
    DBT_DEVICEARRIVAL   =   $8000;   //   system   detected   a   new   device
    DBT_DEVICEREMOVECOMPLETE   =   $8004;   //   device   is   gone
    DBT_DEVTYP_DEVICEINTERFACE   =   $00000005;   //   device   interface   class
Var
    USB:   TUSB;
Implementation
{   TUSB   }
Constructor   TUSB.Create;
Begin
    FWindowHandle   :=   AllocateHWnd(WndProc);
    USBRegister;
End;
Destructor   TUSB.Destroy;
Begin
    DeallocateHWnd(FWindowHandle);
    Inherited   Destroy;
End;
Function   TUSB.USBRegister:   Boolean;
Var
    dbi:   DEV_BROADCAST_DEVICEINTERFACE;
    Size:   Integer;
    r:   Pointer;
Begin
    Result   :=   False;
    Size   :=   Sizeof(DEV_BROADCAST_DEVICEINTERFACE);
    ZeroMemory(@dbi,   Size);
    dbi.dbcc_size   :=   Size;
    dbi.dbcc_devicetype   :=   DBT_DEVTYP_DEVICEINTERFACE;
    dbi.dbcc_reserved   :=   0;
    dbi.dbcc_classguid   :=   GUID_DEVINTERFACE_USB_DEVICE;
    dbi.dbcc_name   :=   0;
    r   :=   RegisterDeviceNotification(FWindowHandle,   @dbi,   DEVICE_NOTIFY_WINDOW_HANDLE);

    If   Assigned(r)   Then
        Result   :=   True;
End;
Procedure   TUSB.WMDeviceChange(Var   Msg:   TMessage);
Var
    devType:   Integer;
    Datos:   PDevBroadcastHdr;
Begin
    If   (Msg.wParam   =   DBT_DEVICEARRIVAL)   Or   (Msg.wParam   =   DBT_DEVICEREMOVECOMPLETE)   Then   Begin
        Datos   :=   PDevBroadcastHdr(Msg.lParam);
        devType   :=   Datos^.dbch_devicetype;
        If   devType   =   DBT_DEVTYP_DEVICEINTERFACE   Then   Begin   //   USB   Device
            If   Msg.wParam   =   DBT_DEVICEARRIVAL   Then   Begin
                If   Assigned(FOnUSBArrival)   Then
                    FOnUSBArrival(Self);
            End
            Else   Begin
                If   Assigned(FOnUSBRemove)   Then
                    FOnUSBRemove(Self);
            End;
        End;
    End;
End;
Procedure   TUSB.WndProc(Var   Msg:   TMessage);
Begin
    If   (Msg.Msg   =   WM_DEVICECHANGE)   Then   Begin
        Try
            WMDeviceChange(Msg);
        Except
            Application.HandleException(Self);
        End;
    End
    Else
        Msg.Result   :=   DefWindowProc(FWindowHandle,   Msg.Msg,   Msg.wParam,   Msg.lParam);
End;
Initialization
    If   Not   Assigned(USB)   Then
        USB   :=   TUSB.Create;
Finalization
    FreeAndNil(USB);
End.


[解决办法]
你把这个文件保存为 USBUnit.pas
之后在你delphi设置lib路径：tools-Environment Options-Library-Library path 加入这个文件路径
或者Component-Unit file name（Browse）加入这个文件

之后声明方法
procedure OnmyUSBArrival(Sender: TObject);
begin
ShowMessage( '插入了！！！ ');
end;

procedure OnmyUSBRemove(Sender: TObject);
begin
ShowMessage( '拔出了！！！ ');
end;

var
MYUSB：TUSB;
begin
MYUSB:=TUSB.Create;
MYUSB.OnUSBRemove:=OnmyUSBRemove;
MYUSB.OnUSBArrival:=OnmyUSBArrival;
MYUSB.free;
end;

当系统有usb插入的时候提示，插入了！
拔出的时候提示，拔出了！