Can't get my ListView Scrollbehavior correct in my simple example

LowLevelM

cross-posted from: https://stackoverflow.com/questions/57079018/qml-cant-get-my-listview-scrollbehavior-correct-in-my-simple-example

Its my first time to use ListView and i need to implement a decent scroll behavior for my application
it "works" but sometimes the animation behavior is a little bit strange

I've wrote a small QML example (runnable with qmlscene tool) to show my problem

alt text

Sample source code:

import QtQuick 2.2
import QtQuick.Window 2.5

Window {
    width: 500
    height: 700
    visible: true

    // my model ctrl is in C++
    // faked it here with pure QML to simplify the example
    ListModel {
        id: cppModel
        // different size - item type depdendend (just const here)
        ListElement { name: "Item 1"; active: false; height: 50 }
        ListElement { name: "Item 2"; active: false; height: 100 }
        ListElement { name: "Item 3"; active: false; height: 150 }
        ListElement { name: "Item 4"; active: false; height: 200 }
        ListElement { name: "Item 5"; active: false; height: 250 }
        ListElement { name: "Item 6"; active: false; height: 300 }

        property int currentItemIndex: -1

        function activate_item(index) {
            // auto deactivate all others
            for(var i = 0; i < rowCount(); i++) {
                var active = (index === i)
                get(i).active = active
                if(active) {
                    currentItemIndex = i
                }
            }
        }
    }

    Component {
        id: listViewDelegate

        Rectangle
        {
            height: model.active ? model.height : 30
            width: 600
            color: "transparent"
            border {color: model.active ? "yellow" : "black"; width: 2}

            Behavior on height {
                NumberAnimation {
                    easing.type: Easing.InCirc
                    duration: 5000
                }
            }

            Text {
                text: model.name;
                font.pixelSize: 24
            }

            MouseArea {
                anchors.fill: parent
                onClicked: {
                    cppModel.activate_item(model.index)
                }
            }
        }
    }

    Rectangle
    {
        width: 400
        height: 600
        border {color: "steelblue"; width: 2}

        ListView {
            id: myList
            anchors.fill: parent
            clip: true
            model: cppModel
            delegate: listViewDelegate

            header: Rectangle {
                width: parent.width; height: 50
                border {color: "red"; width: 2}
                Text {
                    anchors.centerIn: parent
                    text: "Header"
                    font.pixelSize: 32
                }
            }

            highlightMoveDuration: 5000
            highlightMoveVelocity: -1
            highlightResizeDuration: 5000
            highlightResizeVelocity: -1

            preferredHighlightBegin: 0
            preferredHighlightEnd: currentItem.height
            highlightRangeMode: ListView.StrictlyEnforceRange

            snapMode: ListView.SnapToItem

            currentIndex: -1

            onMovementStarted: {
                // show header again
                highlightRangeMode = ListView.ApplyRange
            }
            onCurrentIndexChanged: {
                // highlight current
                highlightRangeMode = ListView.StrictlyEnforceRange
            }
        }

        Connections {
            target: cppModel
            onCurrentItemIndexChanged: { // change comming from C++
                if ( myList.currentIndex !== cppModel.currentItemIndex ) {
                    myList.currentIndex = cppModel.currentItemIndex
                }
            }
        }
    }
}

first: the item that is activated should be scrolled to top (that works) seems ok, only the animation i get are a little strange

my 2 "bad" animation scenarios:

if you activate Item 1..6 downwards, starting with Item 3 the Item Text is moved too far up and then comes back, the up scrolling should always stop at the items top, no bouncing etc. - i've already tried to replace the highlighter but gives me no better result

if you open for example Item 6 and the scroll with mouse to Item 1 and activates item 1, the animation (seems to) first closes the Item 6 and then scrolls the list, better would be that the scrolling/and resize to the activated item 1 is prio and the closing animation of the former item does not block/stutter the item 1 animation

would be glad if someone could kick me in the right direction how to solve the animation problems

thanks

LowLevelM

a played a while with the ListView options but can't get the animations right
so i've tried to implement my own list view like item - as an example how the animation would feel

working sample, with an fake c++ model, with the animations i want to see

import QtQuick 2.5
import QtQuick.Controls 2.5
import QtQuick.Window 2.5

Window {
    width: 500
    height: 700
    visible: true

    // my model ctrl is in C++
    // faked it here with pure QML to simplify the example
    ListModel {
        id: cppModel
        // different size - item type depdendend (just const here)
        ListElement { name: "Item 1"; active: false; height: 100 }
        ListElement { name: "Item 2"; active: false; height: 150 }
        ListElement { name: "Item 3"; active: false; height: 200 }
        ListElement { name: "Item 4"; active: false; height: 250 }
        ListElement { name: "Item 5"; active: false; height: 300 }
        ListElement { name: "Item 6"; active: false; height: 350 }

        property int currentItemIndex: -1

        function activate_item(index) {
            // auto deactivate all others
            for(var i = 0; i < rowCount(); i++) {
                var active = (index === i)
                get(i).active = active
                if(active) {
                    currentItemIndex = i
                }
            }
        }

        function remove_item(index) {
            if(currentItemIndex === -1) {
                console.log("can remove not active item")
                return
            }

            remove(currentItemIndex);
        }

        function deactivate_current_item()
        {
            if(currentItemIndex === -1) {
                console.log("can remove not active item")
                return
            }
            get(currentItemIndex).active = false
        }
    }

    Column {

        Rectangle {
            width: 320
            height: 480

            border { width: 2; color: "steelblue" }

            Flickable {
                id: flickable
                clip: true
                anchors.fill: parent
                contentWidth: 320
                contentHeight: 600

                function goto_header()
                {
                    contentY = 0
                }

                Behavior on contentY {
                    NumberAnimation {
                        easing.type: Easing.OutCubic
                        duration: 500
                    }
                }

                Rectangle {
                    id: myList

                    anchors.top: parent.top
                    anchors.left: parent.left
                    width: flickable.contentWidth
                    height: flickable.contentHeight

                    Column {
                        Rectangle {
                            id: header
                            width: 320
                            height: 40
                            color: "red"
                            border { width: 2; color: "black" }
                            Text { text: "Header"}
                        }

                        Repeater {
                            model: cppModel
                            Rectangle {
                                readonly property int reducedSize: 30
                                width: 320
                                height: model.active ? model.height : reducedSize
                                border { width: 2; color: "black" }
                                Text {
                                    text: model.name
                                }

                                MouseArea {
                                    anchors.fill: parent
                                    onClicked: {
                                        // find new list contentY
                                        // works also if item above is shrinking
                                        // but only if shrinked height is for all items the same
                                        var newContentY = (model.index * reducedSize) + header.height

                                        cppModel.activate_item(model.index)

                                        // scroll to this element
                                        flickable.contentY = newContentY
                                    }
                                }

                                Behavior on height {
                                    NumberAnimation {
                                        easing.type: Easing.OutCubic
                                        duration: 500
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }

        Rectangle {
            height: 100
            width: 320

            Row
            {
                Button {
                    text: "Delete"
                    onClicked: {
                        console.log("Delete clicked")
                        cppModel.remove_item();
                        flickable.goto_header();
                    }
                }
                Button {
                    text: "Save"
                    onClicked: {
                        console.log("Save clicked")
                        cppModel.deactivate_current_item()
                    }
                }
            }
        }
    }
}

Screenshot of the sample program

0_1563517642889_Screenshot from 2019-07-19 08-27-03.png