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Details

Type: Bug
Resolution: Unresolved
Priority: P3: Somewhat important
Fix Version/s: None
Affects Version/s: 5.5.1, 5.6.0 Beta
Component/s: Quick: Layouts
Labels:
None
Environment:
Windows 8.1 64bit, QtCreator 3.6.0

Commits:
f55deac59 (dev), 55b1c49f8 (6.9), ec1e3bb09 (tqtc/lts-6.8), 9141bd2da (tqtc/lts-6.5)

Description

While trying to nest a RowLayout into a ColumnLayout, I encountered these warnings:

<Unknown File>: QML QQuickLayoutAttached: Binding loop detected for property "preferredWidth"

Here is an example which generates three such warnings:

import QtQuick 2.5
import QtQuick.Layouts 1.2

Rectangle {
    id: component_root

    width: 600
    height: 400

    ColumnLayout {
        width: parent.width

        RowLayout {
            Layout.preferredWidth: parent.width
            Layout.fillWidth: false

            spacing: 5

            Rectangle {
                Layout.preferredWidth: 0.4 * parent.width
                Layout.preferredHeight: 20
                Layout.alignment: Qt.AlignCenter
                color: "red"
            }

            Rectangle {
                Layout.preferredWidth: 0.4 * parent.width
                Layout.preferredHeight: 20
                Layout.alignment: Qt.AlignCenter
                color: "blue"
            }
        }
    }
}

Changing spacing to 0 (instead of the current 5) gets rid of the warnings, but I don't understand why the warnings are generated in the first place and even less why they disappear when I set the spacing to 0. As far as I can see, there is no loop in the width, it's all top-down.