Wie zu erkennen, wenn das USB-Gerät ist angeschlossen/nicht angeschlossen?

Diese Aufnahme wurde von erkennen, wenn usb-Gerät angeschlossen ist

 unit U_Usb;

 interface

uses
Windows, Messages, SysUtils, Classes, 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;

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

type

 TComponentUSB = class(TComponent)
   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(AOwner: TComponent); override;
  destructor Destroy; override;
  published
    property OnUSBArrival: TNotifyEvent read FOnUSBArrival write FOnUSBArrival;
    property OnUSBRemove: TNotifyEvent read FOnUSBRemove write FOnUSBRemove;
  end;

  implementation

constructor TComponentUSB.Create(AOwner: TComponent);
   begin
     inherited Create(AOwner);
     FWindowHandle := AllocateHWnd(WndProc);
     USBRegister;
   end;

   destructor TComponentUSB.Destroy;
    begin
   DeallocateHWnd(FWindowHandle);
    inherited Destroy;
   end;

 procedure TComponentUSB.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;

  procedure TComponentUSB.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;

  function TComponentUSB.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;

    end.