Anchors in a loaded file are not working correct - why?

[robro]

Hello,

I have a small problem with anchors.
I do load pages via a loader to a StackLayout.
Somehow the size of the parent (StackLayout) it not populated correctly to the loaded file, so that e.g. in the following example the button is not horizontally centerted.

Why is that and how can I solve that?

Thank you very much!

main.qml

import QtQuick.Controls 2.2
import QtQuick.Layouts 1.3
import QtQuick 2.7


ApplicationWindow {
    id: root
    width: 500
    height: 800
    title: qsTr("Settings")
    visible: true


    header: TabBar {
        id: bar
        width: parent.width
        TabButton {
            text: qsTr("Home")
        }
    }


    StackLayout {
        anchors.fill: parent
        currentIndex: bar.currentIndex

        Item {
            id: envi
            anchors.centerIn: parent
            Loader {
                source: "qrc:/Page1.qml"
            }
        }
    }
}

page1.qml:

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3

Item {
    anchors.centerIn: parent

    Button {
        id: buttonStop
        text: qsTr("Stop")
        font.pixelSize: 18
        anchors.top: parent.top
        anchors.topMargin: 50
        anchors.horizontalCenter: parent.horizontalCenter
    }
}

[Diracsbracket]

@robro
You need to give your Items some dimensions: e.g. the parent of Button is an Item with zero dimensions...

Furthermore, in

StackLayout {
        anchors.fill: parent
        currentIndex: bar.currentIndex

        Item {
            id: envi
            anchors.centerIn: parent
           ....
      }

, the line anchors.centerIn: parent produces the following warning:

qrc:/main.qml:31:9: QML QQuickItem: Detected anchors on an item that is managed by a layout.
This is undefined behavior; use Layout.alignment instead.

so, you can use instead: e.g.

Item {
            id: envi

            //anchors.centerIn: parent //undefined behavior
            Layout.alignment: Qt.AlignVCenter | Qt.AlignHCenter

            width: root.width
            height: root.height
           ...
}

Also give Item in page1.qml some dimensions...

[robro]

Thanks a lot, especially for the additional information :-)