如何让一个应用程序只创建一次,在关闭前,如果双击它的图标只激活这程序的主窗体

Question

如何让一个应用程序只创建一次,在关闭前,如果双击它的图标只激活这程序的主窗体

Answer 1

// usage: just add this unit to your project
unit ZsSingleInstance;interfaceprocedure SingleInstance;implementationuses Windows, Messages, Forms;type
  PShareMem = ^TShareMem;
  TShareMem = record
    AppHandle: THandle;
  end;var
  GMapFileHandle: THandle;
  GShareMem: PShareMem;procedure InitMapFile;
const MAP_FILE_NAME = '{D96D0544-6ADB-408F-9EEF-D1694264C955}';// please change it to your own unique GUID
begin
  // try to open file mapping
  GMapFileHandle := OpenFileMapping(FILE_MAP_ALL_ACCESS, False, PChar(MAP_FILE_NAME));
  // first run
  if GMapFileHandle = 0 then begin
    GMapFileHandle := CreateFileMapping($FFFFFFFF, nil, PAGE_READWRITE, 0, SizeOf(TShareMem), MAP_FILE_NAME);
    GShareMem := MapViewOfFile(GMapFileHandle, FILE_MAP_WRITE or FILE_MAP_READ, 0, 0, 0);
    if GShareMem = nil then CloseHandle(GMapFileHandle)
    else GShareMem^.AppHandle := 0;// set previous app handle to 0 if first run
  end
  else begin// get previous instance shared mem
    GShareMem := MapViewOfFile(GMapFileHandle, FILE_MAP_WRITE or FILE_MAP_READ, 0, 0, 0);
    if GShareMem = nil then CloseHandle(GMapFileHandle);
  end;
end;procedure SingleInstance;
var top_window: HWND;
begin
  try
    if GShareMem <> nil then begin
      if GShareMem^.AppHandle = 0 then GShareMem^.AppHandle := Application.Handle
      else begin
        SendMessage(GShareMem^.AppHandle, WM_SYSCOMMAND, SC_RESTORE, 0);
        top_window := GetLastActivePopup(GShareMem^.AppHandle);
        if (top_window <> 0) and
           (top_window <> GShareMem^.AppHandle) and
           IsWindowVisible(top_window) and
           IsWindowEnabled(top_window) then
          SetForegroundWindow(top_window);// restore last active window
        // terminate current instance
        Halt(0);
      end;
    end;
  except end;
end;initialization
  try// open or create map file
    InitMapFile;
    SingleInstance;
  except end;finalization
  try// free map file
    UnMapViewOfFile(GShareMem);
    CloseHandle(GMapFileHandle);
  except end;end.