Mega Code Archive
Switch between one or many instances
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Title: Switch between one or many instances
Question: Under Win16, you could check the value of hPrevInst at startup.
Under Win32, on hPrevInst you can't rely upon; we can create a uniquely named mutex. But if you want to control instances of forms (not the app) at runtime or change the behaviour at starttime with the commandline, here's a straight solution:
Answer:
The default check of the function is to allow one instance.
But you can control the start of many instances at the commandline prompt with:
: yourApplication.exe /allowinstances
The function itself:
If the window is running and you don't want multiple instance at the command line then no further creation of another instance is possible; the function letAllowInstances() returns false else true.
uses HWND.windows, FindCmdLineSwitch.SysUtils
function letAllowInstances(const mainForm, cmdLine: PAnsiChar): boolean;
var keyWindow: HWND;
begin
result:= false;
keyWindow:= 0;
keyWindow:= FindWindow(mainForm, NIL);
//check if delphi is at design time and creation is allowed
if FindWindow('TAppBuilder',NIL) 0
then keywindow:= 0;
if (keyWindow 0) and not FindCmdLineSwitch(cmdLine, true) then
//then set existing instance
ShowWindow(keyWindow, SW_SHOWNORMAL)
else
result:= true;
end;
and the integration call of the func() into the project-file:
begin
if letAllowInstances('TKeyHandlingDialogForm', 'allowinstances')
then begin
Application.Initialize;
Application.CreateForm(TKeyHandlingDialogForm, KeyHandlingDialogForm);
Application.CreateForm(TPasswordInputDialog, PasswordInputDialog);
Application.CreateForm(TGeneratingKeyDialog, GeneratingKeyDialog);
Application.Run;
end;
end.
FindWindow will return a valid handle if it finds the window class in the current active session (desktop).
While using a mutex will prevent the user to start an application allready running in another session.
Link to mutex solution:
http://www.delphi3000.com/articles/article_870.asp?SK=mutex
-------------------------------------------------------------
Update 13.11.2008
a big tip is to close your application and restart it:
uses ShellAPI;
procedure RestartApplication(sender: TObject);
begin
shellExecute(handle, 'open', PChar(application.ExeName), NIL, NIL,
SW_SHOWNORMAL);
Application.Terminate;
end;
Update 25.6.2009
function winExecAndWait(const sAppPath: string; wVisible: word): boolean
var
si: TStartupInfo;
pi: TProcessInformation;
proc: THandle;
begin
result:= false;
fillChar(si, sizeOf(TStartupInfo),0);
with si do begin
cb:= sizeOf(TStartupInfo);
dwFlags:= STARTF_USESHOWWINDOW OR START_FORCEONFEEDBACK;
wShowWindow:= wVisible;
end;
if NOT CreateProcess(NIL, pChar(sAppPath), NIL, NIL, false,
normal_Priority_class, NIL, NIL, si, pi)
then begin
raise Exception.CreateFmt('error during run'+'errcode %d',
[getLastError]);
end;
proc:= pi.hProcess;
closeHandle(pi.hThread);
if waitForSingleObject(proc, infinite) wait_failed then
result:= true;
closeHandle(proc);
end;
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