How to avoid binding loop when setting padding? - qt

Question

I want to update the padding of a ScrollView if there is a scrollbar visible, but on the other hand, the visibility of the scrollbar is dependent on the height/width of the content inside the scrollbar, which changes when the padding changes. The following causes a binding loop:
ScrollView {
id: control
rightPadding: Scrollbar.vertical.visible ? Scrollbar.vertical.width : 0
....
ScrollBar.vertical: ScrollBar {
parent: control
visible: control.height < height
...
}
}
How can I achieve this without a binding loop? Thanks

Answer 1

I was unable to get your code frag to work - it seems like your code should depend on the contents of your ScrollView, but this is not included in your code frag, and it may be missing some other references.
Anyway, I suggest approaching this a little differently - change the ScrollView's content's width based on whether or not the ScrollBar is visible. I also set the ScrollBar policy instead of visibility. I have created a full example where you can add or remove content using a slider for demonstration:
import QtQuick 2.15
import QtQuick.Layouts 1.12
import QtQuick.Controls 2.12
ApplicationWindow {
id: root
visible: true
height: 500
width: 500
ColumnLayout {
anchors {
fill: parent
}
Slider {
// use slider to add delegates to the ScrollView to toggle the scroll bar visibility
id: slider
to: 20
}
ScrollView {
id: scroll
Layout.fillHeight: true
Layout.fillWidth: true
ScrollBar.vertical.policy: scrollBarVisible ? ScrollBar.AlwaysOn : ScrollBar.AlwaysOff
property bool scrollBarVisible: scroll.contentHeight > scroll.height
ColumnLayout {
width: scroll.scrollBarVisible ? scroll.width - scroll.ScrollBar.vertical.width : scroll.width // change the width of the
Repeater {
model: slider.value
delegate: Rectangle {
color: "tomato"
Layout.fillWidth: true
Layout.preferredHeight: 150
}
}
}
}
}
}
One thing to note though - your ScrollView content cannot have its height depend on its width, for example, if the content had some Text that wraps if there is not enough width, causing it to get taller when the width decreases. This would get back into infinite-loop territory.