ListView -> How to set specific item in specific position

[PawlosCK]

I am trying to set specific item in center of listview, but I don't know how to do that.
Wrong item is visible. When I am trying to change first and last value, visible item is changing, but still is wrong.

I tried to use currentIndex and positionViewAtIndex and it doesn't work as expected.

You can run this using

property var component_infinite: Qt.createComponent("infinite_listview/infinite_listview.qml")
property var object_infinite: component_infinite.createObject(mainWindow)

    object_infinite.visible = true
    object_infinite.setValues(99, 150, 4)

// object_infinite.setValues()

import QtQuick 2.3
import QtQuick.Window 2.15
import QtQuick.Controls 1.4
import QtQuick.Layouts 1.15
import QtQml 2.12

Item
//Window
{
    width: 30
    height: 60
    ListModel
    {
        id: modelID

//        ListElement
//        {
//            itemID: 0
//            number: 0
//        }
    }

    Component
    {
        id: delegateID
        Rectangle
        {
            id: itemDelegate
            height: listviewID.height/3
            width: listviewID.width
            x: 0
            y: 0

            Text
            {
                horizontalAlignment: Text.AlignHCenter
                verticalAlignment: Text.AlignVCenter
                height: parent.height
                width: parent.width
                text: number

                font.pixelSize: parent.height
                fontSizeMode: Text.Fit
            }
        }
    }

    ListView
    {

        onCurrentItemChanged:
        {
            console.log("listviewID.currentIndex: " + listviewID.currentIndex)
            if(listviewID.currentIndex < (modelID.count/2))
            {
                console.log("currentIndex <")
                modelID.move(modelID.count - 1, 0, 1)
            }

            if(listviewID.currentIndex > (modelID.count/2))
            {
                console.log("currentIndex >")
                modelID.move(0, modelID.count - 1, 1)
            }
        }

        id: listviewID

        property var first_value: 0
        property var last_value: 99
        property var fill_length_value: 2
        property var fill_sign_value: '0'

        width: parent.width
        height: parent.height

        //Ucina listview do konkretnego rozmiaru. PRzydatne, gdy uzyje sie opcji preferredHighlightBegin i preferredHighlightEnd
        clip: true

        //Ustawia ilosc widocznego listview na poczatku i na koncu. To jest dodatkowa przestrzen widoczna. PRzydaje sie, zeby elementy plynnie pojawialy sie i znikaly Dane podawane w pikselach.
        preferredHighlightBegin: parent.height/3
        preferredHighlightEnd: parent.height/3
        highlightRangeMode: ListView.StrictlyEnforceRange

        highlightMoveDuration: 1000
        highlightMoveVelocity: -1

        model: modelID
        delegate: delegateID

        Rectangle
        {
            id: current_index_border
            x: 0
            y: parent.height/3
            width: parent.width
            height: parent.height/3
            color: "transparent"
            border.width: 1
        }

        MouseArea
        {
            anchors.fill: parent
            onWheel:
            {
                console.log( listviewID.currentIndex )
                if (wheel.angleDelta.y < 0)
                {
                    console.log("W DOL 1->2")
                    console.log(listviewID.currentIndex)
                    var curr_index_tmp = listviewID.currentIndex
                    if(listviewID.currentIndex < (modelID.count/2))
                    {
                        modelID.move(modelID.count - 1, 0, 1)
                    }

                    listviewID.incrementCurrentIndex()
                }
                else if (wheel.angleDelta.y > 0)
                {
                    console.log("W GORE 2->1")
                    console.log(listviewID.currentIndex)
                    if(listviewID.currentIndex > (modelID.count/2))
                    {
                        modelID.move(0, modelID.count - 1, 1)
                    }
                    listviewID.decrementCurrentIndex()
                }
            }
        }

        Component.onCompleted:
        {

        }
    }

    function setValues(first = 0, last = 59, fill_length = 2, fill_value = '0')
    {
        listviewID.first_value = first
        listviewID.last_value = last
        listviewID.fill_length_value = fill_length
        listviewID.fill_sign_value = fill_value

        var sum = numberOfElements(first, last)
        var half1 = 0
        var half2 = 0

        var resultOfMod = sum % 2
        if (resultOfMod === 0)
        {
            half1 = Math.floor(sum/2)
        }
        else
        {
            half1 = Math.floor(sum/2)
            half2 = sum - half1
        }


        modelID.clear()

        var index = listviewID.last_value - half1
        for (var i = (listviewID.first_value) ; i <= listviewID.last_value; i++)
        {
            console.log("index: " + index + " : i: " + i + " : listviewID.first_value: " + listviewID.first_value)

            if ( index <= listviewID.last_value)
            {
                modelID.append( {"itemID": index, "number": index.toString().padStart(listviewID.fill_length_value, listviewID.fill_sign_value)} )
            }
            else
            {
                index = listviewID.first_value
                modelID.append( {"itemID": index, "number": index.toString().padStart(listviewID.fill_length_value, listviewID.fill_sign_value)} )
            }

            index++
        }

        for (var i = listviewID.first_value, index = 0 ; i <= listviewID.last_value; i++, index++)
        {
            if(modelID.get(index).itemID === 111)
            {
                listviewID.positionViewAtIndex(index, ListView.Center)
                break
            }
        }
    }

    function numberOfElements(a, b)
    {
        //Zwraca ilosc elementow, niezaleznie, czy pierwsza, lub ostatnia liczba jest dodatnia, lub ujemna
        return Math.abs(a-b) + 1
    }
}

I am trying to do that here. Number 111 is value which should be visible in center of listview. Other value is at startup and later, when I am trying to run setValues with values from spinbox.

        for (var i = listviewID.first_value, index = 0 ; i <= listviewID.last_value; i++, index++)
        {
            if(modelID.get(index).itemID === 111)
            {
                listviewID.positionViewAtIndex(index, ListView.Center)
                break
            }
        }

[PawlosCK]

I don't know how it works, but it works. If someone explain how it works, it would be nice. Below full code of control

import QtQuick 2.3
import QtQuick.Window 2.15
import QtQuick.Controls 1.4
import QtQuick.Layouts 1.15
import QtQml 2.12

Item
//Window
{

    id: mainListView

    width: 30
    height: 60
    ListModel
    {
        id: modelID

//        ListElement
//        {
//            itemID: 0
//            number: 0
//        }
    }

    Component
    {
        id: delegateID
        Rectangle
        {
            id: itemDelegate
            height: listviewID.height/3
            width: listviewID.width
            x: 0
            y: 0

            Text
            {
                horizontalAlignment: Text.AlignHCenter
                verticalAlignment: Text.AlignVCenter
                height: parent.height
                width: parent.width
                text: number

                font.pixelSize: parent.height
                fontSizeMode: Text.Fit
            }
        }
    }

    ListView
    {
        onCurrentItemChanged:
        {
            if(listviewID.currentIndex < (modelID.count/2))
            {
                modelID.move(modelID.count - 1, 0, 1)
            }

            if(listviewID.currentIndex > (modelID.count/2))
            {
                modelID.move(0, modelID.count - 1, 1)
            }
        }

        id: listviewID

        property var first_value: 0
        property var last_value: 99
        property var fill_length_value: 2
        property var fill_sign_value: '0'

        width: parent.width
        height: parent.height

        //Ucina listview do konkretnego rozmiaru. PRzydatne, gdy uzyje sie opcji preferredHighlightBegin i preferredHighlightEnd
        clip: true

        //Ustawia ilosc widocznego listview na poczatku i na koncu. To jest dodatkowa przestrzen widoczna. PRzydaje sie, zeby elementy plynnie pojawialy sie i znikaly Dane podawane w pikselach.
        preferredHighlightBegin: parent.height/3
        preferredHighlightEnd: parent.height/3
        highlightRangeMode: ListView.StrictlyEnforceRange

        highlightMoveDuration: 1000
        highlightMoveVelocity: -1

        property bool set_values_first_time: false

        model: modelID
        delegate: delegateID

        Rectangle
        {
            id: current_index_border
            x: 0
            y: parent.height/3
            width: parent.width
            height: parent.height/3
            color: "transparent"
            border.width: 1
        }

        MouseArea
        {
            anchors.fill: parent
            onWheel:
                        {
                            console.log( listviewID.currentIndex )
                            if (wheel.angleDelta.y < 0)
                            {
                                console.log("W DOL 1->2")
                                console.log(listviewID.currentIndex)
                                var curr_index_tmp = listviewID.currentIndex
                                if(listviewID.currentIndex > (modelID.count/2))
                                {
                                    modelID.move(0, modelID.count - 1, 1)
                                    modelID.move(0, modelID.count - 1, 1)
                                    modelID.move(0, modelID.count - 1, 1)
            //                        modelID.move(0, modelID.count - 1, 1)
            //                        modelID.move(0, modelID.count - 1, 1)
                                    listviewID.currentIndex = curr_index_tmp-3
                                }
                                listviewID.incrementCurrentIndex()
                            }
                            else if (wheel.angleDelta.y > 0)
                            {
                                console.log("W GORE 2->1")
                                console.log(listviewID.currentIndex)
                                var curr_index_tmp = listviewID.currentIndex
                                if(listviewID.currentIndex < (modelID.count/2))
                                {
                                    modelID.move(modelID.count - 1, 0, 1)
                                    modelID.move(modelID.count - 1, 0, 1)
                                    modelID.move(modelID.count - 1, 0, 1)
            //                        modelID.move(modelID.count - 1, 0, 1)
            //                        modelID.move(modelID.count - 1, 0, 1)
                                    listviewID.currentIndex = curr_index_tmp+3
                                }
                                listviewID.decrementCurrentIndex()
                            }
                        }

        }

        Component.onCompleted:
        {
        }
    }

    function setValues(first = 0, last = 59, fill_length = 2, fill_value = '0')
    {
        listviewID.first_value = Number(first)
        listviewID.last_value = Number(last)
        listviewID.fill_length_value = Number(fill_length)
        listviewID.fill_sign_value = fill_value

        var sum = numberOfElements(listviewID.first_value, listviewID.last_value)
        var half1 = 0
        var half2 = 0

        var resultOfMod = sum % 2
        if (resultOfMod === 0)
        {
            half1 = Math.floor(sum/2)
        }
        else
        {
            half1 = Math.floor(sum/2)
            half2 = sum - half1
        }

        modelID.clear()
        for (var index_tmp = listviewID.last_value - half1, i = listviewID.first_value ; i <= listviewID.last_value; i++, index_tmp++)
        {
            console.log("index_tmp: " + index_tmp + " : i: " + i + " : listviewID.first_value: " + listviewID.first_value)
            if ( index_tmp <= listviewID.last_value)
            {
                modelID.append( {"itemID": index_tmp, "number": index_tmp.toString().padStart(listviewID.fill_length_value, listviewID.fill_sign_value)} )
            }
            else
            {
                index_tmp = listviewID.first_value
                modelID.append( {"itemID": index_tmp, "number": index_tmp.toString().padStart(listviewID.fill_length_value, listviewID.fill_sign_value)} )
            }
        }

        listviewID.currentIndex = -1    //Z tym ustaiwniem, poprawnie sie ustawia na 0, ale uzywajac scroola, przeskakuje w dzziwne miejsce
        for (var i = listviewID.first_value, index_tmp = 0 ; i <= listviewID.last_value; i++, index_tmp++)
        {

            if(modelID.get(index_tmp).itemID === listviewID.first_value)
            {
                listviewID.positionViewAtIndex(index_tmp, ListView.Center)
                if(listviewID.set_values_first_time === false)
                {
                    listviewID.currentIndex = index_tmp-2
                }
                else
                {
                    listviewID.currentIndex = index_tmp
                }


                break
            }
        }
        listviewID.set_values_first_time = true
    }

    function numberOfElements(a, b)
    {
        //Zwraca ilosc elementow, niezaleznie, czy pierwsza, lub ostatnia liczba jest dodatnia, lub ujemna
        return Math.abs(a-b) + 1
    }
}