title: Qt QML binding child property to parent property
body: <p>I want to set the ApplicationWindow to minimum width and height by the minimum width and height of the child element "mainLayout". I am having trouble to use the property of "mainLayout" in the parent QML ApplicationWindow. I tried to make the property viewable by making an alias. Not sure if it is the right solution. It does not work. But there is also no Error when I run.</p>
  
  <p>My code looks like this:</p>
  
  <p>main.qml</p>
  
  <pre><code>import QtQuick 2.2
  import QtQuick.Controls 1.2
  import QtQuick.Layouts 1.3
  import QtQuick.Window 2.2
  
  ApplicationWindow {
  visible: true
  width: 1500
  height: 1200
  property int margin: 11
  
  minimumWidth: serial.mainLayout.minimumWidth + 2 * margin //this one is not working
  minimumHeight: serial.mainLayout.minimumHeight + 2 * margin //this one is not working
  
  
  Serial {
          id: serial
          anchors.fill: parent
      }
  }
  </code></pre>
  
  <p>Serial.qml</p>
  
  <pre><code>import QtQuick 2.7
  import QtQuick.Controls 1.4
  import QtQuick.Layouts 1.3
  import io.qt.serialComm 1.0
  
  Item {
  
      anchors.fill: parent
      id: item
      property alias mainLayout: mainLayout
  
      ColumnLayout {
          id: wrapper
          width: parent.width/2
          height: parent.height/2
  
          ColumnLayout {
              id: mainLayout
              anchors.fill: parent
              anchors.margins: margin
              GroupBox {
                  id: rowBox
                  title: "Row layout"
                  Layout.fillWidth: true
  
                  RowLayout {
                      id: rowLayout
                      anchors.fill: parent
                      TextField {
                          placeholderText: "This wants to grow horizontally"
                          Layout.fillWidth: true
                      }
                      Button {
                          text: "Button"
                      }
                  }
              }
  
              GroupBox {
                  id: gridBox
                  title: "Grid layout"
                  Layout.fillWidth: true
  
                  GridLayout {
                      id: gridLayout
                      rows: 3
                      flow: GridLayout.TopToBottom
                      anchors.fill: parent
  
                      Label { text: "Line 1" }
                      Label { text: "Line 2" }
                      Label { text: "Line 3" }
  
                      TextField { }
                      TextField { }
                      TextField { }
  
                      TextArea {
                          text: "This widget spans over three rows in the GridLayout.\n"
                              + "All items in the GridLayout are implicitly positioned from top to bottom."
                          Layout.rowSpan: 3
                          Layout.fillHeight: true
                          Layout.fillWidth: true
                      }
                  }
              }
              TextArea {
                  id: t3
                  text: "This fills the whole cell"
                  Layout.minimumHeight: 30
                  Layout.fillHeight: true
                  Layout.fillWidth: true
              }
              GroupBox {
                  id: stackBox
                  title: "Stack layout"
                  implicitWidth: 200
                  implicitHeight: 60
                  Layout.fillWidth: true
                  Layout.fillHeight: true
                  StackLayout {
                      id: stackLayout
                      anchors.fill: parent
  
                      function advance() { currentIndex = (currentIndex + 1) % count }
  
                      Repeater {
                          id: stackRepeater
                          model: 5
                          Rectangle {
                              color: Qt.hsla((0.5 + index)/stackRepeater.count, 0.3, 0.7, 1)
                              Button { anchors.centerIn: parent; text: "Page " + (index + 1); onClicked: { stackLayout.advance() } }
                          }
                      }
                  }
              }
          }
      }
  }
  </code></pre>
  
  <p>When I put the code in one file, it works and the ApplicationWindow does not get smaller than the minimum height and width of the child element "mainLayout". But splitting into 2 files does not work..</p>