- Qt 5.3
- Qt Quick
- QML Dynamic View Ordering Tutorial 3 - Moving Dragged Items
- Qt 5.3.2 Reference Documentation

QML Dynamic View Ordering Tutorial 2 - Dragging View Items QML Dynamic View Ordering Tutorial 4 - Sorting Items

# QML Dynamic View Ordering Tutorial 3 - Moving Dragged Items

The next step in our application to move items within the list as they're dragged so that we can re-order the list. To achieve this we introduce three new types to our application; VisualDataModel, Drag and DropArea.

    Rectangle {
        id: root

        width: 300; height: 400

        Component {
            id: dragDelegate

            MouseArea {
                id: dragArea

                property bool held: false

                anchors { left: parent.left; right: parent.right }
                height: content.height

                drag.target: held ? content : undefined
                drag.axis: Drag.YAxis

                onPressAndHold: held = true
                onReleased: held = false

                Rectangle {
                    id: content
                    Drag.active: dragArea.held
                    Drag.source: dragArea
                    Drag.hotSpot.x: width / 2
                    Drag.hotSpot.y: height / 2
                }
                DropArea {
                    anchors { fill: parent; margins: 10 }

                    onEntered: {
                        visualModel.items.move(
                                drag.source.DelegateModel.itemsIndex,
                                dragArea.DelegateModel.itemsIndex)
                    }
                }
            }
        }
    }

### Walkthrough

In order to re-order the view we need to determine when one item has been dragged over another. With the Drag attached property we can generate events that are sent to the scene graph whenever the item it is attached to moves.

                    Drag.active: dragArea.held
                    Drag.source: dragArea
                    Drag.hotSpot.x: width / 2
                    Drag.hotSpot.y: height / 2

Drag events are only sent while the active property is true, so in this example the first event would be sent when the delegate was held with additional event sents when dragging. The hotSpot property specifies the relative position of the drag events within the dragged item, the center of the item in this instance.

Then we use a DropArea in each view item to determine when the hot spot of the dragged item intersects another item, when a drag enters one of these DropAreas we can move the dragged item to the index of the item it was dragged over.

                DropArea {
                    anchors { fill: parent; margins: 10 }

                    onEntered: {
                        visualModel.items.move(
                                drag.source.DelegateModel.itemsIndex,
                                dragArea.DelegateModel.itemsIndex)
                    }
                }

To move the items within the view we use a VisualDataModel. The VisualDataModel type is used by the view types to instantiate delegate items from model data and when constructed explicitly can be used to filter and re-order the model items provided to ListView. The items property of VisualDataModel provides access to the view's items and allows us to change the visible order without modifying the source model. To determine the current visible index of the items we use itemsIndex property on the VisualDataModel attached property of the delegate item.

To utilize a VisualDataModel with a ListView we bind it to the model property of the view and bind the model and delegate to the VisualDataModel.

        DelegateModel {
            id: visualModel

            model: PetsModel {}
            delegate: dragDelegate
        }

        ListView {
            id: view

            anchors { fill: parent; margins: 2 }

            model: visualModel

            spacing: 4
            cacheBuffer: 50
        }

Files:

- tutorials/dynamicview/dynamicview3/PetsModel.qml
- tutorials/dynamicview/dynamicview3/dynamicview.qml
- tutorials/dynamicview/dynamicview3/dynamicview3.qmlproject

QML Dynamic View Ordering Tutorial 2 - Dragging View Items QML Dynamic View Ordering Tutorial 4 - Sorting Items