Fórum Como abir aplicação somente uma vez #403536

var
  HprevHist : HWND;
Begin
  frmSplash := TfrmSplash.Create(Application);
  frmSplash.Show;
  frmSplash.Update;
  sleep(5);

  HprevHist := FindWindow(Nil, PChar('NOME_SISTEMA'));
  if HprevHist = 0 then begin
    Application.Title := 'NOME_SISTEMA';
    frmSplash.Hide;
    frmSplash.Close;
    frmSplash.Free;
    Application.CreateForm(TfrmPrincipal, frmPrincipal);
    Application.Run;
  end else
    Application.MessageBox(Pchar('O Aplicativo já esta sendo Executado '), 'Erro.', MB_ICONERROR);
end.

program Vendas;
uses
  Forms,
  Windows, Messages,
  uPrincipal in 'uPrincipal.pas' ,
  uDMPrincipal in 'uDMPrincipal.pas' {DM: TDataModule},
  uModeloCadastro in 'uModeloCadastro.pas' ;
{$R *.res}
var
  HprevHist : HWND;
begin
  HprevHist := FindWindow(Nil, PChar('Vendas'));
  if HprevHist = 0 then 
  begin
  
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.Title := 'Sistema de Vendas';
  Application.CreateForm(TDM, DM);
  Application.CreateForm(TfrmPrincipal, frmPrincipal);
  Application.CreateForm(TfrmModelo, frmModelo);
  Application.Run;
  end else
  Application.MessageBox(Pchar('Sistema já está em execução!'), 'Erro', MB_ICONERROR);
end.

var
MutexHandle: THandle;
hwind:HWND;

begin
  MutexHandle:= CreateMutex(nil,True,AppVendas);
  if MutexHandle  0 then
  begin
    if GetLastError = ERROR_ALREADY_EXISTS then
    begin
      MessageBox(0,Sistema aberto em outra Janela!,,mb_IconHand);
      CloseHandle(MutexHandle);
      hwind:=0;
      repeat
      hwind:= Windows.FindWindowEx(0,hwind,TApplication,AppVendas);
      until(hwindApplication.Handle);
      if (hwind0) then
  begin
    Windows.ShowWindow(hwind,SW_SHOWNORMAL);
    Windows.SetForegroundWindow(hwind);
  end;
    Halt;
    end
  end;