ListItemDragHandle.qml

/*
*   Copyright (C) 2018 by Marco Martin <mart@kde.org>
*
*   This program is free software; you can redistribute it and/or modify
*   it under the terms of the GNU Library General Public License as
*   published by the Free Software Foundation; either version 2, or
*   (at your option) any later version.
*
*   This program is distributed in the hope that it will be useful,
*   but WITHOUT ANY WARRANTY; without even the implied warranty of
*   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*   GNU Library General Public License for more details
*
*   You should have received a copy of the GNU Library General Public
*   License along with this program; if not, write to the
*   Free Software Foundation, Inc.,
*   51 Franklin Street, Fifth Floor, Boston, MA  2.010-1301, USA.
*/

import QtQuick 2.6
import QtQuick.Layouts 1.2
import org.kde.kirigami 2.4 as Kirigami

Item {
    id: root

    property Item listItem

    property ListView listView

    signal moveRequested(int oldIndex, int newIndex)

    
    signal dropped()

    implicitWidth: Kirigami.Units.iconSizes.smallMedium
    implicitHeight: implicitWidth

    MouseArea {
        id: mouseArea
        anchors.fill: parent
        drag {
            target: listItem
            axis: Drag.YAxis
            minimumY: 0
            maximumY: listView.height - listItem.height
        }
        Kirigami.Icon {
            id: internal
            source: "handle-sort"
            property int startY
            property int mouseDownY
            property Item originalParent
            property int autoScrollThreshold: listItem.height * 3
            opacity: mouseArea.pressed || (!Kirigami.Settings.tabletMode && listItem.hovered) ? 1 : 0.6

            function arrangeItem() {
                var newIndex = listView.indexAt(1, listView.contentItem.mapFromItem(listItem, 0, 0).y + internal.mouseDownY);

                if (Math.abs(listItem.y - internal.startY) > height && newIndex > -1 && newIndex !== index) {
                    root.moveRequested(index, newIndex);
                }
            }

            anchors.fill: parent
        }
        preventStealing: true
        

        onPressed: {
            internal.originalParent = listItem.parent;
            listItem.parent = listView;
            listItem.y = internal.originalParent.mapToItem(listItem.parent, listItem.x, listItem.y).y;
            internal.originalParent.z = 99;
            internal.startY = listItem.y;
            internal.mouseDownY = mouse.y;
        }

        onPositionChanged: {
            if (!pressed) {
                return;
            }
            internal.arrangeItem();

            scrollTimer.interval = 500 * Math.max(0.1, (1-Math.max(internal.autoScrollThreshold - listItem.y, listItem.y - listView.height + internal.autoScrollThreshold + listItem.height) / internal.autoScrollThreshold));
            scrollTimer.running = (listItem.y < internal.autoScrollThreshold ||
                        listItem.y > listView.height - internal.autoScrollThreshold);
        }
        onReleased: {
            listItem.y = internal.originalParent.mapFromItem(listItem, 0, 0).y;
            listItem.parent = internal.originalParent;
            dropAnimation.running = true;
            scrollTimer.running = false;
            root.dropped();
        }
        onCanceled: released()
        SequentialAnimation {
            id: dropAnimation
            YAnimator {
                target: listItem
                from: listItem.y 
                to: 0
                duration: Kirigami.Units.longDuration
                easing.type: Easing.InOutQuad
            }
            PropertyAction {
                target: listItem.parent
                property: "z"
                value: 0
            }
        }
        Timer {
            id: scrollTimer
            interval: 500
            repeat: true
            onTriggered: {
                if (listItem.y < internal.autoScrollThreshold) {
                    listView.contentY = Math.max(0, listView.contentY - Kirigami.Units.gridUnit)
                } else {
                    listView.contentY = Math.min(listView.contentHeight - listView.height, listView.contentY + Kirigami.Units.gridUnit)
                }
                internal.arrangeItem();
            }
        }
    }
}