unit MultInst;

interface

uses
Windows ,Messages, SysUtils, Classes, Forms;

implementation

const
STR_UNIQUE = '{2BE6D96E-827F-4BF9-B33E-8740412CDE96}';
MI_ACTIVEAPP = 1; {激活应用程序}
MI_GETHANDLE = 2; {取得句柄}

var
iMessageID : Integer;
OldWProc : TFNWndProc;
MutHandle : THandle;
BSMRecipients : DWORD;

function NewWndProc(Handle: HWND; Msg: Integer; wParam, lParam: Longint):
Longint; stdcall;
begin
Result := 0;
if Msg = iMessageID then
begin
case wParam of
MI_ACTIVEAPP: {激活应用程序}
if lParam<>0 then
begin
{收到消息的激活前一个实例}
{为什么要在另一个程序中激活?}
{因为在同一个进程中SetForegroundWindow并不能把窗体提到最前}
if IsIconic(lParam) then
OpenIcon(lParam)
else
SetForegroundWindow(lParam);
Application.Terminate; {终止本实例}
end;
MI_GETHANDLE: {取得程序句柄}
begin
PostMessage(HWND(lParam), iMessageID, MI_ACTIVEAPP,
Application.Handle);
end;
end;
end
else
Result := CallWindowProc(OldWProc, Handle, Msg, wParam, lParam);
end;

procedure InitInstance;
begin
{取代应用程序的消息处理}
OldWProc := TFNWndProc(SetWindowLong(Application.Handle, GWL_WNDPROC,
Longint(@NewWndProc)));

{打开互斥对象}
MutHandle := OpenMutex(MUTEX_ALL_ACCESS, False, STR_UNIQUE);
if MutHandle = 0 then
begin
{建立互斥对象}
MutHandle := CreateMutex(nil, False, STR_UNIQUE);
end
else begin
Application.ShowMainForm := False;
{已经有程序实例,广播消息取得实例句柄}
BSMRecipients := BSM_APPLICATIONS;
BroadCastSystemMessage(BSF_IGNORECURRENTTASK or BSF_POSTMESSAGE,
@BSMRecipients, iMessageID, MI_GETHANDLE,Application.Handle);
end;
end;

initialization
{注册消息}
iMessageID := RegisterWindowMessage(STR_UNIQUE);
InitInstance;

finalization
{还原消息处理过程}
if OldWProc <> Nil then
SetWindowLong(Application.Handle, GWL_WNDPROC, LongInt(OldWProc));

{关闭互斥对象}
if MutHandle <> 0 then CloseHandle(MutHandle);

end.