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<H1><A NAME="api0">How Can I Prevent Multiple Instances of My Application?</A></H1>
<H2> Solution 1</H2>
<I><P>From: "David S. Lee" <davidlee@crl.com></P>
</I><P>This is the way I do it:</P>
<P>In the begin..end block of the .dpr:</P>
<PRE>begin
if HPrevInst <>0 then begin
ActivatePreviousInstance;
Halt;
end;
end;</PRE>
<P>Here is the unit I use:</P>
<HR><PRE>unit PrevInst;
interface
uses
WinProcs,
WinTypes,
SysUtils;
type
PHWnd = ^HWnd;
function EnumApps(Wnd: HWnd; TargetWindow: PHWnd): bool; export;
procedure ActivatePreviousInstance;
implementation
function EnumApps(Wnd: HWnd; TargetWindow: PHWnd): bool;
var
ClassName : array[0..30] of char;
begin
Result := true;
if GetWindowWord(Wnd, GWW_HINSTANCE) = HPrevInst then begin
GetClassName(Wnd, ClassName, 30);
if STRIComp(ClassName,'TApplication')=0 then begin
TargetWindow^ := Wnd;
Result := false;
end;
end;
end;
procedure ActivatePreviousInstance;
var
PrevInstWnd: HWnd;
begin
PrevInstWnd := 0;
EnumWindows(@EnumApps,LongInt(@PrevInstWnd));
if PrevInstWnd <> 0 then
if IsIconic(PrevInstWnd) then
ShowWindow(PrevInstWnd,SW_Restore)
else
BringWindowToTop(PrevInstWnd);
end;
end.</PRE><HR>
<H2> Solution 2</H2>
<I><P>From: "The Graphical Gnome" <rdb@ktibv.nl></P>
</I><P>Taken from Delphi 2 Developers Guide by Pacheco and Teixeira with heavy modifications.</P>
<P>Usage: In the Project source change to the following </P>
<HR><PRE>if InitInstance then
begin
Application.Initialize;
Application.CreateForm(TFrmSelProject, FrmSelProject);
Application.Run;
end;
unit multinst;
{
Taken from Delphi 2 Developers Guide by Pacheco and Teixeira
With heavy Modifications.
Usage:
In the Project source change to the following
if InitInstance then
begin
Application.Initialize;
Application.CreateForm(TFrmSelProject, FrmSelProject);
Application.Run;
end;
That's all folks ( I hope ;()
}
interface
uses Forms, Windows, Dialogs, SysUtils;
const
MI_NO_ERROR = 0;
MI_FAIL_SUBCLASS = 1;
MI_FAIL_CREATE_MUTEX = 2;
{ Query this function to determine if error occurred in startup. }
{ Value will be one or more of the MI_* error flags. }
function GetMIError: Integer;
Function InitInstance : Boolean;
implementation
const
UniqueAppStr : PChar; {Change for every Application}
var
MessageId: Integer;
WProc: TFNWndProc = Nil;
MutHandle: THandle = 0;
MIError: Integer = 0;
function GetMIError: Integer;
begin
Result := MIError;
end;
function NewWndProc(Handle: HWND; Msg: Integer; wParam,
lParam: Longint): Longint; StdCall;
begin
{ If this is the registered message... }
if Msg = MessageID then begin
{ if main form is minimized, normalize it }
{ set focus to application }
if IsIconic(Application.Handle) then begin
Application.MainForm.WindowState := wsNormal;
ShowWindow(Application.Mainform.Handle, sw_restore);
end;
SetForegroundWindow(Application.MainForm.Handle);
end
{ Otherwise, pass message on to old window proc }
else
Result := CallWindowProc(WProc, Handle, Msg, wParam, lParam);
end;
procedure SubClassApplication;
begin
{ We subclass Application window procedure so that }
{ Application.OnMessage remains available for user. }
WProc := TFNWndProc(SetWindowLong(Application.Handle, GWL_WNDPROC,
Longint(@NewWndProc)));
{ Set appropriate error flag if error condition occurred }
if WProc = Nil then
MIError := MIError or MI_FAIL_SUBCLASS;
end;
procedure DoFirstInstance;
begin
SubClassApplication;
MutHandle := CreateMutex(Nil, False, UniqueAppStr);
if MutHandle = 0 then
MIError := MIError or MI_FAIL_CREATE_MUTEX;
end;
procedure BroadcastFocusMessage;
{ This is called when there is already an instance running. }
var
BSMRecipients: DWORD;
begin
{ Don't flash main form }
Application.ShowMainForm := False;
{ Post message and inform other instance to focus itself }
BSMRecipients := BSM_APPLICATIONS;
BroadCastSystemMessage(BSF_IGNORECURRENTTASK or BSF_POSTMESSAGE,
@BSMRecipients, MessageID, 0, 0);
end;
Function InitInstance : Boolean;
begin
MutHandle := OpenMutex(MUTEX_ALL_ACCESS, False, UniqueAppStr);
if MutHandle = 0 then
begin
{ Mutex object has not yet been created, meaning that no previous }
{ instance has been created. }
ShowWindow(Application.Handle, SW_ShowNormal);
Application.ShowMainForm:=True;
DoFirstInstance;
result := True;
end
else
begin
BroadcastFocusMessage;
result := False;
end;
end;
initialization
begin
UniqueAppStr := Application.Exexname;
MessageID := RegisterWindowMessage(UniqueAppStr);
ShowWindow(Application.Handle, SW_Hide);
Application.ShowMainForm:=FALSE;
end;
finalization
begin
if WProc <> Nil then
{ Restore old window procedure }
SetWindowLong(Application.Handle, GWL_WNDPROC, LongInt(WProc));
end;
end.</PRE><HR>
<H2> Solution 3</H2>
<I><P>From: "Jerzy A.Radzimowski" <jerzyara@odn.zgora.pl></P>
</I>
<HR><PRE>VAR MutexHandle:THandle;
Var UniqueKey : string;
FUNCTION IsNextInstance:BOOLEAN;
BEGIN
Result:=FALSE;
MutexHandle:=0;
MutexHandle:=CREATEMUTEX( NIL,TRUE, UniqueKey);
IF MutexHandle<>0 THEN
BEGIN
IF GetLastError=ERROR_ALREADY_EXISTS THEN
BEGIN
Result:=TRUE;
CLOSEHANDLE(MutexHandle);
MutexHandle:=0;
END;
END;
END;
begin
CmdShow:=SW_HIDE;
MessageId:=RegisterWindowMessage(zAppName);
Application.Initialize;
IF IsNextInstance
THEN
PostMessage(HWND_BROADCAST, MessageId,0,0)
ELSE
BEGIN
Application.ShowMainForm:=FALSE;
Application.CreateForm(TMainForm, MainForm);
MainForm.StartTimer.Enabled:=TRUE;
Application.Run;
END;
IF MutexHandle<>0 THEN CLOSEHANDLE(MutexHandle);
end.</PRE><HR>
<P>in MainForm you need add code for process private message</P>
<HR><PRE>PROCEDURE TMainForm.OnAppMessage( VAR M:TMSG; VAR Ret:BOOLEAN );
BEGIN
IF M.Message=MessageId THEN
BEGIN
Ret:=TRUE;
// BringWindowToTop !!!!!!!!
END;
END;
INITIALIZATION
ShowWindow(Application.Handle, SW_Hide);
END.</PRE><HR>
<!---------------------------------------------------------------------------------------------------------------------------------------------------->
<H1><A NAME="api1">Performing an action when Windows shuts down a Delphi app</A></H1>
<I><P>From: wesjones@hooked.net (Wes Jones)</P>
</I><P>I did a little investigation, and here is what seems to be happening:</P>
<P>Normally, when you exit a Delphi application by using the system menu or by calling the Form's Close method,
the following event handlers are called:</P>
<OL>
<LI> FormCloseQuery - the default action sets the variable CanClose=TRUE so form close will continue.
<LI>FormClose
<LI>FormDestroy
</OL>
<P>If the application is active and you attempt to exit Windows, the event handlers are called in the following sequence:</P>
<OL>
<LI>FormCloseQuery
<LI> FormDestroy
</OL>
<P>The FormClose method never seems to be called.</P>
<P>Here is the flow of events when the user chooses to end the Windows session:</P>
<OL>
<LI>Windows sends out a WM_QUERYENDSESSION message to all application windows one by one and awaits a response
<LI>Each application window receives the message and returns a non-zero value if it is OK to terminate, or 0 if it is not OK to terminate.
<LI>If any application returns 0, the Windows session is not ended, otherwise, Windows sends a WM_ENDSESSION message to all
application windows
<LI>Each Application Window responds with a TRUE value indicating that Windows can terminate any
time after all applications have returned from processing this message. This appears to be the location of the Delphi problem:
Delphi applications seem to return TRUE and the FormDestroy method is called immediately, bypassing the FormClose method.
<LI>Windows exits
</OL>
<P>One solution is to respond to the WM_QUERYENDSESSION message in the Delphi application and prevent Windows
from exiting by returning a 0 result. This can't be done in the FormCloseQuery method because there is no way to
determine the source of the request (it can either be the result of the WM_QUERYENDSESSION message or the user just simply
closing the application). </P>
<P>Another solution is to respond to the WM_QUERYENDSESSION message by calling the same cleanup procedure you call in
the FormClose method.</P>
<P>Example:</P>
<HR><PRE>unit Unit1;
interface
uses
SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls, Forms,
Dialogs;
type
TForm1 = class(TForm)
procedure FormClose(Sender: TObject; var Action: TCloseAction);
private
{---------------------------------------------------------------}
{ Custom procedure to respond to the WM_QUERYENDSESSION message }
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