delphi中application．messagebox和messagebox有什么区别？

Application是Form单元的一个全局对象
具体实现是
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function TApplication.MessageBox(const Text, Caption: PChar; Flags: Longint): Integer;
var
  ActiveWindow: HWnd;
  WindowList: Pointer;
  MBMonitor, AppMonitor: HMonitor;
  MonInfo: TMonitorInfo;
  Rect: TRect;
  FocusState: TFocusState;
begin
  ActiveWindow := GetActiveWindow;
  MBMonitor := MonitorFromWindow(ActiveWindow, MONITOR_DEFAULTTONEAREST);
  AppMonitor := MonitorFromWindow(Handle, MONITOR_DEFAULTTONEAREST);
  if MBMonitor <> AppMonitor then
  begin
    MonInfo.cbSize := Sizeof(TMonitorInfo);
    GetMonitorInfo(MBMonitor, @MonInfo);
    GetWindowRect(Handle, Rect);
    SetWindowPos(Handle, 0,
      MonInfo.rcMonitor.Left + ((MonInfo.rcMonitor.Right - MonInfo.rcMonitor.Left) div 2),
      MonInfo.rcMonitor.Top + ((MonInfo.rcMonitor.Bottom - MonInfo.rcMonitor.Top) div 2),
      0, 0, SWP_NOACTIVATE or SWP_NOREDRAW or SWP_NOSIZE or SWP_NOZORDER);
  end;
  WindowList := DisableTaskWindows(0);
  FocusState := SaveFocusState;
  if UseRightToLeftReading then Flags := Flags or MB_RTLREADING;
  try
    Result := Windows.MessageBox(Handle, Text, Caption, Flags);
  finally
    if MBMonitor <> AppMonitor then
      SetWindowPos(Handle, 0,
        Rect.Left + ((Rect.Right - Rect.Left) div 2),
        Rect.Top + ((Rect.Bottom - Rect.Top) div 2),
        0, 0, SWP_NOACTIVATE or SWP_NOREDRAW or SWP_NOSIZE or SWP_NOZORDER);
    EnableTaskWindows(WindowList);
    SetActiveWindow(ActiveWindow);
    RestoreFocusState(FocusState);
  end;
end;
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MessageBox是Windows单元的函数
可以看到Application.MessageBox调用了Windows.MessageBox

编译时要包含相应的单元
比如用到Application.Messagebox就包含Form
用到MessageBox要包含WIndows