Mega Code Archive
Allow only one instance of your application
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Title: Allow only one instance of your application
Question: How to prevent a second launch of your application ?
Answer:
var AtomText: array[0..31] of Char;
procedure LookForPreviousInstance;
var
PreviousInstanceWindow : hWnd;
AppName : array[0..30] of char;
FoundAtom : TAtom;
begin
// put the app name into AtomText
StrFmt(AtomText, 'OnlyOne%s', [Copy(Application.Title,1,20)]);
// check to see if there's a global atom based on the app name
FoundAtom := GlobalFindAtom(AtomText);
if FoundAtom 0 then // another instance exists
begin
StrFmt(AppName,'%s', [Application.Title]);
// change current title so that FindWindow doesn't see it
Application.ShowMainForm := false;
Application.Title := 'destroy me';
// locate the previous instance of the app
PreviousInstanceWindow := FindWindow(nil,AppName);
// give focus to the previous instance of the app
// stop the current instance of the application
Application.Terminate;
if PreviousInstanceWindow 0 then
if IsIconic(PreviousInstanceWindow) then
ShowWindow(PreviousInstanceWindow,SW_RESTORE)
else SetForegroundWindow(PreviousInstanceWindow);
end;
// make the global atom so no other instances can occur
FoundAtom := GlobalAddAtom(AtomText);
end;
constructor TForm.Create(AOwner: TComponent);
begin
inherited;
LookForPreviousInstance;
...
end;
destructor TForm.Destroy;
var
FoundAtom : TAtom;
ValueReturned : word;
begin
// must not forget to remove the global atom, so first check to see if
// there's a global atom already
FoundAtom := GlobalFindAtom(AtomText);
if FoundAtom 0 then ValueReturned := GlobalDeleteAtom(FoundAtom);
inherited Destroy;
end;
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