DragScrollHelper.qml

import QtQuick 2.7

Item {
    id: root

    property Flickable flickable: parent
    anchors.fill: parent

    property MouseArea mouseArea
    readonly property bool active: flickable && (mouseArea ? mouseArea.drag.active : false)
    readonly property real mouseY: active ? mouseArea.mapToItem(root, 0, mouseArea.mouseY).y : 0
    readonly property real mousex: active ? mouseArea.mapToItem(root, mouseArea.mouseX, 0).x : 0

    property real maxVelocity: 600
    property real velocityPerDistance: 10

    property int interval: 5
    readonly property real maxStep: maxVelocity / (1000 / interval)
    readonly property real stepPerDistance: velocityPerDistance / (1000 / interval)

    Timer {
        running: root.active && root.mouseY < 0 && !root.flickable.atYBeginning
        triggeredOnStart: true
        repeat: true
        interval: root.interval
        onTriggered: flickable.contentY -= Math.min(root.maxStep, -root.mouseY * root.stepPerDistance)
    }

    Timer {
        running: root.active && root.mouseY > root.height && !root.flickable.atYEnd
        triggeredOnStart: true
        repeat: true
        interval: root.interval
        onTriggered: root.flickable.contentY += Math.min(root.maxStep, (root.mouseY - root.height) * root.stepPerDistance)
    }

    Connections {
        enabled: active
        target: listView
        onContentYChanged: fakeDraggedMove()
    }

    function fakeDraggedMove() {
        var dragged = mouseArea.drag.target;
        --dragged.y;
        ++dragged.y;
    }

    Text {
        anchors.right: parent.right
        text: active ? mouseArea.drag.target.y : ''
    }

    DropArea {
        parent: flickable
        anchors.fill: parent
        onEntered: {
            drag.accepted = false;

            var source = drag.source;
            if (!source)
                return;

            var mouseArea;
            if (source.drag)
                mouseArea = source;
            else if (source.parent.drag)
                mouseArea = source.parent;
            else if (source.mouseArea)
                mouseArea = source.mouseArea;

            if (ancestorOf(flickable, mouseArea))
                root.mouseArea = mouseArea;

        }
    }

    function ancestorOf(ancestor, item) {
        if (!item)
            return false;

        while (item.parent) {
            if (item.parent === ancestor)
                return true;
            item = item.parent;
        }
        return false;
    }
}