QWidget::winId() failed to get native window

1.setQuitOnLastWindowClosed(true);

2.create a widget

3.use QWidget::winId() to get a native window

4.use NSView *view = (NSView*)widget->winId() conver to NSView , and it works.

On the first time I can get a native NSView, but if i close the widget by click the native close button, and then I call show() to make the widget visible again. After that, the value winId() returned is no longer a valid NSView.