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// Component to detect when usb devices are connected or disconnected
// using RegisterDeviceNotification

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.