Improve code for detecting USB drive insertion & removal
Dear Experts,
Please refer to the included code which detects when a USB device is connected or disconnected.
It worked perfectly for me. As you can see it handles the Windows message WM_DEVICECHANGE.
However as it stands its not that flexible for easily adding to a project..
It would be nice to have this in a self-contained unit that generates suitable events when a USB device is attached or removed. I would prefer that it not be made into a component that I have to install, in order to produce more portable code.
I don't know if its possible to handle a message without a form, but maybe it could be a small non-visible dummy form.
If it seems possible I would appreciate a working Delphi 5 compatible version.
Many thanks!
Please refer to the included code which detects when a USB device is connected or disconnected.
It worked perfectly for me. As you can see it handles the Windows message WM_DEVICECHANGE.
However as it stands its not that flexible for easily adding to a project..
It would be nice to have this in a self-contained unit that generates suitable events when a USB device is attached or removed. I would prefer that it not be made into a component that I have to install, in order to produce more portable code.
I don't know if its possible to handle a message without a form, but maybe it could be a small non-visible dummy form.
If it seems possible I would appreciate a working Delphi 5 compatible version.
Many thanks!
unit USBDetectF;
{taken from an Experts Exchange solution:
http://www.experts-exchange.com/Programming/Languages/Pascal/Delphi/
Q_21552015.html?sfQueryTermInfo=1+drive+letter+usb
ginsonic:
Here is a complete sample project. Use a form and a label.
}
interface
uses
Windows, Messages, Classes, Forms, Controls, StdCtrls, Buttons;
type
TUSBDetectForm = class(TForm)
Label1: TLabel;
BitBtn1: TBitBtn;
Label2: TLabel;
Label3: TLabel;
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
protected
procedure WMDEVICECHANGE(var Msg: TMessage); message WM_DEVICECHANGE;
public
{ Public declarations }
end;
var
USBDetectForm: TUSBDetectForm;
{----------------------------------------------------------------------------}
// Device constants
const
DBT_DEVICEARRIVAL = $00008000;
DBT_DEVICEREMOVECOMPLETE = $00008004;
DBT_DEVTYP_VOLUME = $00000002;
// Device structs
type
_DEV_BROADCAST_HDR = packed record
dbch_size: DWORD;
dbch_devicetype: DWORD;
dbch_reserved: DWORD;
end;
DEV_BROADCAST_HDR = _DEV_BROADCAST_HDR;
TDevBroadcastHeader = DEV_BROADCAST_HDR;
PDevBroadcastHeader = ^TDevBroadcastHeader;
type
_DEV_BROADCAST_VOLUME = packed record
dbch_size: DWORD;
dbch_devicetype: DWORD;
dbch_reserved: DWORD;
dbcv_unitmask: DWORD;
dbcv_flags: WORD;
end;
DEV_BROADCAST_VOLUME = _DEV_BROADCAST_VOLUME;
TDevBroadcastVolume = DEV_BROADCAST_VOLUME;
PDevBroadcastVolume = ^TDevBroadcastVolume;
implementation
{$R *.dfm}
procedure TUSBDetectForm.WMDEVICECHANGE(var Msg: TMessage);
var lpdbhHeader: PDevBroadcastHeader;
lpdbvData: PDevBroadcastVolume;
dwIndex: Integer;
lpszDrive: String;
begin
// Perform inherited
inherited;
// Get the device notification header
lpdbhHeader:=PDevBroadcastHeader(Msg.lParam);
// Handle the message
lpszDrive:='Drive ';
case Msg.WParam of
DBT_DEVICEARRIVAL : {a USB drive was connected}
begin
if (lpdbhHeader^.dbch_devicetype = DBT_DEVTYP_VOLUME) then
begin
lpdbvData:=PDevBroadcastVolume(Msg.lParam);
for dwIndex :=0 to 25 do
begin
if ((lpdbvData^.dbcv_unitmask shr dwIndex) = 1) then
begin
lpszDrive:=lpszDrive+Chr(65+dwIndex)+':';
break;
end;
end;
Label1.Caption:=lpszDrive + ' connected';
end;
end;
DBT_DEVICEREMOVECOMPLETE: {a USB drive was removed}
begin
if (lpdbhHeader^.dbch_devicetype = DBT_DEVTYP_VOLUME) then
begin
lpdbvData:=PDevBroadcastVolume(Msg.lParam);
for dwIndex:=0 to 25 do
begin
if ((lpdbvData^.dbcv_unitmask shr dwIndex) = 1) then
begin
lpszDrive:=lpszDrive+Chr(65+dwIndex)+':';
break;
end;
end;
Label1.Caption:=lpszDrive + ' removed';
end;
end;
end;
end;
procedure TUSBDetectForm.FormCreate(Sender: TObject);
begin
Label1.Caption := '';
end;
end.
Do more with
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i'm assuming any other object would do, provided we have a mechanism for capturing the windows messages
use below snippet like :
uses UsbDetector, StrUtils;
procedure TForm1.Usb(Sender: TObject; Drive: string; Attached: boolean);
begin
ShowMessage(Drive + IfThen(Attached, 'connected', 'disconnected'));
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
StartUsbDetector(Usb);
end;
use below snippet like :
uses UsbDetector, StrUtils;
procedure TForm1.Usb(Sender: TObject; Drive: string; Attached: boolean);
begin
ShowMessage(Drive + IfThen(Attached, 'connected', 'disconnected'));
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
StartUsbDetector(Usb);
end;
unit UsbDetector;
interface
uses Classes;
type
TUsbDriveChanged = procedure (Sender: TObject; Drive: string; Attached: boolean) of object;
procedure StartUsbDetector(NotifyProc: TUsbDriveChanged);
procedure StopUsbDetector;
implementation
uses Windows, Messages, Forms, SysUtils;
type
TUSBDetector = class(TObject)
private
fUsbDriveChanged: TUsbDriveChanged;
protected
procedure DeviceChanged(Msg: UINT; wParam, lParam: Longint);
procedure DoUsbDriveChanged(Drive: string; Attached: Boolean); dynamic;
public
constructor Create(NotifyProc: TUsbDriveChanged);
destructor Destroy; override;
property OnUsbDriveChanged: TUsbDriveChanged read fUsbDriveChanged;
end;
var mUSBDetector: TUSBDetector;
procedure StartUsbDetector(NotifyProc: TUsbDriveChanged);
begin
if not Assigned(mUsbDetector) then
mUsbDetector := TUsbDetector.Create(NotifyProc);
end;
procedure StopUsbDetector;
begin
FreeAndNil(mUsbDetector);
mUsbDetector := nil;
end;
{----------------------------------------------------------------------------}
// Device constants
const
DBT_DEVICEARRIVAL = $00008000;
DBT_DEVICEREMOVECOMPLETE = $00008004;
DBT_DEVTYP_VOLUME = $00000002;
// Device structs
type
_DEV_BROADCAST_HDR = packed record
dbch_size: DWORD;
dbch_devicetype: DWORD;
dbch_reserved: DWORD;
end;
DEV_BROADCAST_HDR = _DEV_BROADCAST_HDR;
TDevBroadcastHeader = DEV_BROADCAST_HDR;
PDevBroadcastHeader = ^TDevBroadcastHeader;
type
_DEV_BROADCAST_VOLUME = packed record
dbch_size: DWORD;
dbch_devicetype: DWORD;
dbch_reserved: DWORD;
dbcv_unitmask: DWORD;
dbcv_flags: WORD;
end;
DEV_BROADCAST_VOLUME = _DEV_BROADCAST_VOLUME;
TDevBroadcastVolume = DEV_BROADCAST_VOLUME;
PDevBroadcastVolume = ^TDevBroadcastVolume;
var
fPrevWndProc: TFNWndProc = nil;
function UsbWndProc(hWnd: HWND; Msg: UINT; wParam, lParam: Longint): Longint; stdcall;
begin
Result := CallWindowProc(fPrevWndProc, hWnd, Msg, wParam, lParam);
if (Msg = WM_DEVICECHANGE) and (mUsbDetector <> nil) then
mUsbDetector.DeviceChanged(Msg, wParam, lParam);
end;
constructor TUSBDetector.Create(NotifyProc: TUsbDriveChanged);
begin
inherited Create;
fUsbDriveChanged := NotifyProc;
fPrevWndProc := TFNWndProc(GetWindowLong(Application.Handle, GWL_WNDPROC));
SetWindowLong(Application.Handle, GWL_WNDPROC, LongInt(@UsbWndProc));
end;
destructor TUSBDetector.Destroy;
begin
//SetWindowLong(Application.Handle, GWL_WNDPROC, LongInt(@fPrevWndProc));
inherited Destroy;
end;
procedure TUSBDetector.DeviceChanged(Msg: UINT; wParam, lParam: LongInt);
var
lpdbhHeader: PDevBroadcastHeader;
lpdbvData: PDevBroadcastVolume;
dwIndex: Integer;
lpszDrive: string;
begin
// Get the device notification header
lpdbhHeader := PDevBroadcastHeader(lParam);
// Handle the message
lpszDrive := 'Drive ';
case WParam of
DBT_DEVICEARRIVAL: {a USB drive was connected}
begin
if lpdbhHeader^.dbch_devicetype = DBT_DEVTYP_VOLUME then
begin
lpdbvData := PDevBroadcastVolume(lParam);
for dwIndex := 0 to 25 do
begin
if (lpdbvData^.dbcv_unitmask shr dwIndex) = 1 then
begin
lpszDrive := lpszDrive + Chr(65 + dwIndex) + ':';
break;
end;
end;
DoUsbDriveChanged(lpszDrive, True);
end;
end;
DBT_DEVICEREMOVECOMPLETE: {a USB drive was removed}
begin
if lpdbhHeader^.dbch_devicetype = DBT_DEVTYP_VOLUME then
begin
lpdbvData := PDevBroadcastVolume(lParam);
for dwIndex := 0 to 25 do
begin
if (lpdbvData^.dbcv_unitmask shr dwIndex) = 1 then
begin
lpszDrive := lpszDrive + Chr(65 + dwIndex) + ':';
break;
end;
end;
DoUsbDriveChanged(lpszDrive, False);
end;
end;
end;
end;
procedure TUSBDetector.DoUsbDriveChanged(Drive: string; Attached: Boolean);
begin
if Assigned(fUsbDriveChanged) then
fUsbDriveChanged(Self, Drive, Attached);
end;
end.
stopping the UsbDetector gave an error, dunno why it doesn't want to put the old WndProc back
Closing the application gave AV priviliged instruction
with below code changes it should be solved
Closing the application gave AV priviliged instruction
with below code changes it should be solved
constructor TUSBDetector.Create(NotifyProc: TUsbDriveChanged);
begin
inherited Create;
fUsbDriveChanged := NotifyProc;
if not Assigned(fPrevWndProc) then
begin
fPrevWndProc := TFNWndProc(GetWindowLong(Application.Handle, GWL_WNDPROC));
SetWindowLong(Application.Handle, GWL_WNDPROC, LongInt(@UsbWndProc));
end;
end;
procedure StopUsbDetector;
begin
FreeAndNil(mUsbDetector);
end;
Hi!
Thanks for a great solution that does *exactly* what I wanted! So nice to get a solution where you can just copy and paste it into Delphi without having to add missing identifiers or debug it first! I just made a minor change to suit my preferences (to the returned Drive string)
Some of your code is outside my Delphi level so it will be great to go through it and learn some new techniques.
Mike
Thanks for a great solution that does *exactly* what I wanted! So nice to get a solution where you can just copy and paste it into Delphi without having to add missing identifiers or debug it first! I just made a minor change to suit my preferences (to the returned Drive string)
Some of your code is outside my Delphi level so it will be great to go through it and learn some new techniques.
Mike
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