Mega Code Archive
USB and RegisterDeviceNotification
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Title: USB and RegisterDeviceNotification
Question: how do you can detect if a usb device is connected or disconnected?
Answer:
// 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.
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