Loader will disturb the layout of the header of ApplicationWindow(QtQuick 2)

[tham]

This is easier to explain by the example. Following codes work as expected

main.qml

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.0

ApplicationWindow {
    visible: true
    width: 640
    height: 480        

    header: CustomToolBar{

    }
}

CustomToolBar.qml

import QtQuick 2.6
import QtQuick.Controls 2.0

ToolBar {
    id : toolBar

    /*Loader{
        id: loader
    }//*/

    Row{
        spacing: 20
        anchors.fill: parent

        ToolButton {
            contentItem: Image {
                fillMode: Image.PreserveAspectFit
                horizontalAlignment: Image.AlignHCenter
                verticalAlignment: Image.AlignVCenter
                source: "qrc:/icons/settings.svg"
                sourceSize.width: 40
                width: sourceSize.width
            }            
        }
    }
}

Without the loader, the result looks good, the icon is within the Toolbar.

If I enable the loader, the icon will offset a little bit, this make the view looks bad

How could I fix this issue?Thanks

[Roumed]

@tham if i'm not mistaking, the height of the header becomes smaller.
This is about using the only element to make layout of the header.
Try to set header height equals to row containing your toolbuttons explicitly.

[jpnurmi]

A quote the docs:

If only a single item is used within the ToolBar, it will resize to fit the implicit size of its contained item.

If you add multiple children into ToolBar, it can no longer use the implicit size of the content, and falls back to the default height.