Binding loop detection seems very sensitive

fcarney

I found this trivial bind that was created in my code. I wanted to signal off the change of a value that was not a property of value injected by a ListView to a delegate which is called: update_. So I made it assign a value to a property called refresh.

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Binding Loop")

    property bool bind: true

    property bool update_: false

    property bool refresh: update_
    onRefreshChanged: {
        console.log("refresh", refresh)
        if(refresh){
            if(bind){
                update_ = false
            }else{
                Qt.callLater(resetUpdate)
            }
        }
    }

    function resetUpdate(){
        update_ = false
    }

    Component.onCompleted: update_ = true
}

Anytime it changes update_ it will change refresh and trigger the onRefreshChanged. What is interesting to me is that it detects a binding loop on the second call. It seems to me this would be a common use case. So having be this sensitive is also interesting to me. But if I use a Binding {} object or use Qt.callLater I can avoid this binding loop error. I don't remember this being this sensitive before. But I do remember creating binding loops that locked my machine up. So maybe it is for the better.

fcarney

Which begs the question: Can I provide just a signal from a model to a delegate?
I suppose I could change it to an int and just accumulate the change so there is no updating of the value by the detection code. I am already treating it like an event anyway. It is probably an indication of code smell in the design anyway.

fcarney

BTW, out of curiosity, I found you can break the detection this way and create programs that will lock up. So be careful:

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Binding Loop")

    property bool bind: false

    property bool update_: false

    property bool refresh: update_
    onRefreshChanged: {
        console.log("refresh", refresh)
        if(refresh){
            if(bind){
                update_ = false
            }else{
                Qt.callLater(resetUpdate)
            }
        }
    }

    function resetUpdate(){
        update_ = false

        //Qt.callLater(()=>{update_ = true}) // can easily break detection
    }

    Component.onCompleted: update_ = true
}