Answer:
Typically, an application does not need to be notified when a session switch
occurs. However, if the application needs to be aware when its desktop is
current, it can register for session switch notifications. Applications that
access the serial port or another shared resource on the computer should
check for this. To register for a notification, use the following function:
function WTSRegisterSessionNotification(
hWnd: HWND; // Window handle
dwFlags: DWORD // Flags
): Bool; // Return value
The registered HWND receives the message WM_WTSSESSION_CHANGE
through its WindowProc function.
In dwFlags you can specify:
a) NOTIFY_FOR_THIS_SESSION. A window is notified only about the session
change events that affect the session to which window belongs.
b) NOTIFY_FOR_ALL_SESSIONS. A window is notified for all session change
events.
The action happening on the session can be found in wParam code, which may
contain one of the following flags.
WTS_CONSOLE_CONNECT: A session was connected to the console session.
WTS_CONSOLE_DISCONNECT: A session was disconnected from the console session.
WTS_REMOTE_CONNECT: A session was connected to the remote session.
WTS_REMOTE_DISCONNECT: A session was disconnected from the remote session.
WTS_SESSION_LOGON: A user has logged on to the session.
WTS_SESSION_LOGOFF: A user has logged off the session.
WTS_SESSION_LOCK: A session has been locked.
WTS_SESSION_UNLOCK: A session has been unlocked.
WTS_SESSION_REMOTE_CONTROL: A session has changed its remote controlled status.
lParam contains the sessionId for the session affected.
When your process no longer requires these notifications or is terminating,
it should call the following to unregister its notification.
function WTSUnRegisterSesssionNotification(
hWnd: HWND // window handle.
): Boolean; // Result
The HWND values passed to WTSRegisterSessionNotification are reference
counted, so you must call WTSUnRegisterSessionNotification exactly the same
number of times that you call WTSRegisterSessionNotification.
Applications can use the WTS_CONSOLE_CONNECT, WTS_CONSOLE_DISCONNECT,
WTS_REMOTE_CONNECT, WTS_REMOTE_DISCONNECT messages to track their state, as
well as to release and acquire console specific resources.
{********************************************************************
Unit Wtsapi
********************************************************************}
Unit Wtsapi;
interface
{
Copyright(c) By Thomas Stutz
Date: 10. April 2002
Version: 1.0.0
}
uses
Windows;
const
// The WM_WTSSESSION_CHANGE message notifies applications of changes in session state.
WM_WTSSESSION_CHANGE = $2B1;
// wParam values:
WTS_CONSOLE_CONNECT = 1;
WTS_CONSOLE_DISCONNECT = 2;
WTS_REMOTE_CONNECT = 3;
WTS_REMOTE_DISCONNECT = 4;
WTS_SESSION_LOGON = 5;
WTS_SESSION_LOGOFF = 6;
WTS_SESSION_LOCK = 7;
WTS_SESSION_UNLOCK = 8;
WTS_SESSION_REMOTE_CONTROL = 9;
// Only session notifications involving the session attached to by the window
// identified by the hWnd parameter value are to be received.
NOTIFY_FOR_THIS_SESSION = 0;
// All session notifications are to be received.
NOTIFY_FOR_ALL_SESSIONS = 1;
function RegisterSessionNotification(Wnd: HWND; dwFlags: DWORD): Boolean;
function UnRegisterSessionNotification(Wnd: HWND): Boolean;
function GetCurrentSessionID: Integer;
implementation
function RegisterSessionNotification(Wnd: HWND; dwFlags: DWORD): Boolean;
// The RegisterSessionNotification function registers the specified window
// to receive session change notifications.
// Parameters:
// hWnd: Handle of the window to receive session change notifications.
// dwFlags: Specifies which session notifications are to be received:
// (NOTIFY_FOR_THIS_SESSION, NOTIFY_FOR_ALL_SESSIONS)
type
TWTSRegisterSessionNotification = function(Wnd: HWND; dwFlags: DWORD): BOOL; stdcall;
var
hWTSapi32dll: THandle;
WTSRegisterSessionNotification: TWTSRegisterSessionNotification;
begin
Result := False;
hWTSAPI32DLL := LoadLibrary('Wtsapi32.dll');
if (hWTSAPI32DLL > 0) then
begin
try @WTSRegisterSessionNotification :=
GetProcAddress(hWTSAPI32DLL, 'WTSRegisterSessionNotification');
if Assigned(WTSRegisterSessionNotification) then
begin
Result:= WTSRegisterSessionNotification(Wnd, dwFlags);
end;
finally
if hWTSAPI32DLL > 0 then
FreeLibrary(hWTSAPI32DLL);
end;
end;
end;
function UnRegisterSessionNotification(Wnd: HWND): Boolean;
// The RegisterSessionNotification function unregisters the specified window
// Parameters:
// hWnd: Handle to the window
type
TWTSUnRegisterSessionNotification = function(Wnd: HWND): BOOL; stdcall;
var
hWTSapi32dll: THandle;
WTSUnRegisterSessionNotification: TWTSUnRegisterSessionNotification;
begin
Result := False;
hWTSAPI32DLL := LoadLibrary('Wtsapi32.dll');
if (hWTSAPI32DLL > 0) then
begin
try @WTSUnRegisterSessionNotification :=
GetProcAddress(hWTSAPI32DLL, 'WTSUnRegisterSessionNotification');
if Assigned(WTSUnRegisterSessionNotification) then
begin
Result:= WTSUnRegisterSessionNotification(Wnd);
end;
finally
if hWTSAPI32DLL > 0 then
FreeLibrary(hWTSAPI32DLL);
end;
end;
end;
function GetCurrentSessionID: Integer;
// Getting the session id from the current process
type
TProcessIdToSessionId = function(dwProcessId: DWORD; pSessionId: DWORD): BOOL; stdcall;
var
ProcessIdToSessionId: TProcessIdToSessionId;
hWTSapi32dll: THandle;
Lib : THandle;
pSessionId : DWord;
begin
Result := -1;
Lib := GetModuleHandle('kernel32');
if Lib <> 0 then
begin
ProcessIdToSessionId := GetProcAddress(Lib, '1ProcessIdToSessionId');
if Assigned(ProcessIdToSessionId) then
begin
ProcessIdToSessionId(GetCurrentProcessId(), DWORD(@pSessionId));
Result:= pSessionId;
end;
end;
end;
end.
{********************************************************************
Example:
********************************************************************}
unit Unit1;
interface
uses
Windows, Messages, {...}, Wtsapi;
type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
{ Private declarations }
FRegisteredSessionNotification : Boolean;
procedure AppMessage(var Msg: TMSG; var HAndled: Boolean);
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.AppMessage(var Msg: TMSG; var Handled: Boolean);
var
strReason: string;
begin
Handled := False;
// Check for WM_WTSSESSION_CHANGE message
if Msg.Message = WM_WTSSESSION_CHANGE then
begin
case Msg.wParam of
WTS_CONSOLE_CONNECT:
strReason := 'WTS_CONSOLE_CONNECT';
WTS_CONSOLE_DISCONNECT:
strReason := 'WTS_CONSOLE_DISCONNECT';
WTS_REMOTE_CONNECT:
strReason := 'WTS_REMOTE_CONNECT';
WTS_REMOTE_DISCONNECT:
strReason := 'WTS_REMOTE_DISCONNECT';
WTS_SESSION_LOGON:
strReason := 'WTS_SESSION_LOGON';
WTS_SESSION_LOGOFF:
strReason := 'WTS_SESSION_LOGOFF';
WTS_SESSION_LOCK:
strReason := 'WTS_SESSION_LOCK';
WTS_SESSION_UNLOCK:
strReason := 'WTS_SESSION_UNLOCK';
WTS_SESSION_REMOTE_CONTROL:
begin
strReason := 'WTS_SESSION_REMOTE_CONTROL';
// GetSystemMetrics(SM_REMOTECONTROL);
end;
else
strReason := 'WTS_Unknown';
end;
// Write strReason to a Memo
Memo1.Lines.Add(strReason + ' ' + IntToStr(msg.Lparam));
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
// register the window to receive session change notifications.
FRegisteredSessionNotification := RegisterSessionNotification(Handle, NOTIFY_FOR_THIS_SESSION);
Application.OnMessage := AppMessage;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
// unregister session change notifications.
if FRegisteredSessionNotification then
UnRegisterSessionNotification(Handle);
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
// retrieve current session ID
ShowMessage(Inttostr(GetCurrentSessionID));
end;
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