There are components available on the Delphi sites that provide this
functionality for you if you want the easy way out. The most reliable
method of ensuring only one instance of your application is running is to
use a mutex (MUTual EXclusive). Take a look at the CreateMutex function in
the Win32 API help file for more info. From memory, it goes something like
this.
var
Mutex: THandle;
begin
Application.Title := 'MyApplicationName';
{ Check for another application instance. }
Mutex := CreateMutex(nil, False, PChar(Application.Title + 'Mutex'));
if GetLastError = ERROR_ALREADY_EXISTS then
Exit;
Application.CreateForm(TForm1, Form1);
Application.Run;
end;
**************************************************
and (separate code to create a mutex)...
***************** START PROJECT FILE EXAMPLE ****************
program Project1;
uses
Forms,
Windows, // necessary for the THandle and CreateMutex
Unit1 in 'Unit1.pas' {Form1};
{$R *.RES}
var
AppMutex : THandle;
begin
AppMutex := CreateMutex(nil, true, 'MY_APP_MUTEX_NAME');
if GetLastError <> ERROR_ALREADY_EXISTS then begin
Application.Initialize;
Application.CreateForm(TForm1, Form1);
Application.Run;
end;
end.
***************** END PROJECT FILE EXAMPLE ****************