qml 弹出窗口的Z序问题

1、pop窗口：窗口为parent的子控件，并非独立窗口，z序和父窗口一样

Popup {
         id: popup
         x: 0
         y: 0            
         parent: Overlay.overlay
         width: 300
         height: 500
         modal: true // 使弹出窗口为模态
         focus: true // 设置弹出窗口获得焦点

         background: Rectangle {
                color: "red"
         }
         closePolicy: Popup.CloseOnEscape | Popup.CloseOnPressOutside

         contentItem: Text {
                text: qsTr("Hello!")
                color: "black"
                font.pixelSize: 14
                horizontalAlignment: Text.AlignHCenter
                verticalAlignment: Text.AlignVCenter
        }
}

id：popup显示时会至于父窗口上方

2、设计一个独立窗口：MyDialog.qml

import QtQuick 2.0
import QtQuick.Window 2.12
import QtQuick.Controls 2.12

Window {
    id: dialog
    width: 500
    height: 300
    title: "MyDialog"
    color: "transparent"
    signal back
    
    flags: Qt.FramelessWindowHint | Qt.Window
    
}

CNCDialog {
     id: dlg
｝

独立窗口，Z序高于父窗口，同时也高于其他父窗口的子窗口