NSSavePanel获取取消按钮对象

Question

我想显示相对于＆＃34;取消＆＃34;我的NSSavePanel按钮，但这似乎不可能。这是一个示例代码，解释了我需要做的事情：

    // the save panel is called when the _window3 get closed..
[panel beginSheetModalForWindow:_window3 completionHandler:^(NSInteger result)
  {

      if (result == NSFileHandlingPanelOKButton)
      {

          // ok, saving my file! (also the app get closed)
      }
      else
      {
          /* (the app get closed w/o saving anything ATM)
           but... you are really sure????
           Since you have done a long job with this app you can also push the button by mistake.. (OMG)

           Nice should be to add a Popover relative to the cancel button rect, where the user can see and push
           on a "go back" and the "Exit w/o saving" buttons
           */

          // normally I call a popover this way:
          [_goBackOrExitPopover showRelativeToRect:[cancelBtn bounds] ofView:cancelBtn preferredEdge:NSMinYEdge];
           // ... but how to intercept the cancel button (cancelBtn)??
      }
  }];

如何找到取消按钮对象？