qml问题之Loader二次show时继承父类窗口层次的解决

环境：win10；Qt Creator 4.11.2；Qt 5.14.2

前言：qml的Loader加载窗口时有时候不想释放资源而是想要hide()窗口，这是会出现一个问题，那就是二次show时会出现重继承Loader父类窗口的层次。

现象：窗口visible=false时，窗口继承窗口层次

解决：quitOnLastWindowClosed设置为true(默认)；在onClosing槽函数里用opacity=0.0替换掉 visible=false方法；让窗口一直可视也就规避了这个规律。然后设置close.accepted = false规避掉quitOnLastWindowClosed这个窗口决策。

onClosing官方说明:

closing(CloseEvent close)

This signal is emitted when the user tries to close the window.

This signal includes a close parameter. The close.accepted property is true by default so that the window is allowed to close; but you can implement an onClosing handler and set close.accepted = false if you need to do something else before the window can be closed.

The corresponding handler is onClosing.

This signal was introduced in Qt 5.1.