Delphi 讓程序只運行一次[高人寫的代碼]

unit RunOne;
interface
const
  MI_QUERYWINDOWHANDLE = 1;
  MI_RESPONDWINDOWHANDLE = 2;
  MI_ERROR_NONE = 0;
  MI_ERROR_FAILSUBCLASS = 1;
  MI_ERROR_CREATINGMUTEX = 2;
// Call this function to determine if error occurred in startup.
// Value will be one or more of the MI_ERROR_* error flags.
function GetMIError: Integer;

implementation
uses Forms, Windows, SysUtils;

const
  UniqueAppStr = 'NewCQ';

 
var
  MessageId: Integer;
  WProc: TFNWndProc;
  MutHandle: THandle;
  MIError: Integer;

function GetMIError: Integer;
begin
  Result := MIError;
end;

function NewWndProc(Handle: HWND; Msg: Integer; wParam, lParam: Longint):
  Longint; stdcall;
begin
  Result := 0;
// If this is the registered message...
  if Msg = MessageID then
  begin
    case wParam of
      MI_QUERYWINDOWHANDLE:
// A new instance is asking for main window handle in order
// to focus the main window, so normalize app and send back
// message with main window handle.
        begin
          if IsIconic(Application.Handle) then
          begin
            Application.MainForm.WindowState := wsNormal;
            Application.Restore;
          end;
          PostMessage(HWND(lParam), MessageID, MI_RESPONDWINDOWHANDLE,
            Application.MainForm.Handle);
        end;
      MI_RESPONDWINDOWHANDLE:
// The running instance has returned its main window handle,
// so we need to focus it and go away.
        begin
          SetForegroundWindow(HWND(lParam));
          Application.Terminate;
        end;
    end;
  end
// Otherwise, pass message on to old window proc
  else
    Result := CallWindowProc(WProc, Handle, Msg, wParam, lParam);
end;

procedure SubClassApplication;
begin
// We subclass Application window procedure so that
// Application.OnMessage remains available for user.
  WProc := TFNWndProc(SetWindowLong(Application.Handle, GWL_WNDPROC,
    Longint(@NewWndProc)));
// Set appropriate error flag if error condition occurred
  if WProc = nil then
    MIError := MIError or MI_ERROR_FAILSUBCLASS;
end;

procedure DoFirstInstance;
// This is called only for the first instance of the application
begin
// Create the mutex with the (hopefully) unique string
  MutHandle := CreateMutex(nil, False, UniqueAppStr);
  if MutHandle = 0 then
    MIError := MIError or MI_ERROR_CREATINGMUTEX;
end;

procedure BroadcastFocusMessage;
// This is called when there is already an instance running.
var
  BSMRecipients: DWORD;
begin
// Prevent main form from flashing
  Application.ShowMainForm := False;
// Post message to try to establish a dialogue with previous instance
  BSMRecipients := BSM_APPLICATIONS;
  BroadCastSystemMessage(BSF_IGNORECURRENTTASK or BSF_POSTMESSAGE,
    @BSMRecipients, MessageID, MI_QUERYWINDOWHANDLE,
    Application.Handle);
end;

procedure InitInstance;
begin
  SubClassApplication; // hook application message loop
  MutHandle := OpenMutex(MUTEX_ALL_ACCESS, False, UniqueAppStr);
  if MutHandle = 0 then
// Mutex object has not yet been created, meaning that no previous
// instance has been created.
    DoFirstInstance
  else
    BroadcastFocusMessage;
end;
initialization
  MessageID := RegisterWindowMessage(UniqueAppStr);
  InitInstance;
finalization
// Restore old application window procedure
  if WProc <> nil then
    SetWindowLong(Application.Handle, GWL_WNDPROC, LongInt(WProc));
  if MutHandle <> 0 then CloseHandle(MutHandle); // Free mutex
end.