UTILISER LES MESSAGES WINDOWS POUR GERER LE NOMBRE D'INSTANCES

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Panel1: TPanel;
    procedure FormCreate(Sender: TObject);
  private
    { Déclarations privées }
    procedure DefaultHandler(var Msg);override;
  public
    { Déclarations publiques }
  end;

var
  Form1: TForm1;
  MessageSys:UINT;

implementation

{$R *.dfm}

procedure TForm1.DefaultHandler(var Msg);
begin
  inherited DefaultHandler(Msg);
  if TMessage(Msg).Msg=MessageSys then
    case TMessage(Msg).WParam of
      0:if TMessage(Msg).LParam<>Application.Handle Then
          //if MessageDlg('New Instance is about to start,Start it?',mtConfirmation,[mbYes,mbNo],0)=mrNo then
            begin
              SendMessage(HWND_BROADCAST,MessageSys,1,application.Handle);
            end;
      1:if TMessage(Msg).LParam<>Application.handle then
          begin
            application.Terminate;
          end;
    end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  MessageSys:=RegisterWindowMessage('MsgOneInst12');
  SendMessage(HWND_BROADCAST,MessageSys,0,Application.Handle);
end;

end.