DragHandler QML Type | Qt Quick (original) (raw)

Handler for dragging. More...

Properties

Signals

Detailed Description

DragHandler is a handler that is used to interactively move an Item. Like other Input Handlers, by default it is fully functional, and manipulates its target.

It has properties to restrict the range of dragging.

If it is declared within one Item but is assigned a different target, then it handles events within the bounds of the parent Item but manipulates the target Item instead:

import QtQuick

Item { width: 640 height: 480

[Rectangle](qml-qtquick-rectangle.html) {
    id: feedback
    border.color: "red"
    width: Math.max(10, handler.centroid.ellipseDiameters.width)
    height: Math.max(10, handler.centroid.ellipseDiameters.height)
    radius: Math.max(width, height) / 2
    visible: handler.active
}

[DragHandler](qml-qtquick-draghandler.html) {
    id: handler
    target: feedback
}

}

A third way to use it is to set target to null and react to property changes in some other way:

import QtQuick

Item { width: 640 height: 480

[DragHandler](qml-qtquick-draghandler.html) {
    id: handler
    target: null
}

[Text](qml-qtquick-text.html) {
    color: handler.active ? "darkgreen" : "black"
    text: handler.centroid.position.x.toFixed(1) + "," + handler.centroid.position.y.toFixed(1)
    x: handler.centroid.position.x - width / 2
    y: handler.centroid.position.y - height
}

}

If minimumPointCount and maximumPointCount are set to values larger than 1, the user will need to drag that many fingers in the same direction to start dragging. A multi-finger drag gesture can be detected independently of both a (default) single-finger DragHandler and a PinchHandler on the same Item, and thus can be used to adjust some other feature independently of the usual pinch behavior: for example adjust a tilt transformation, or adjust some other numeric value, if the target is set to null. But if the target is an Item, centroid is the point at which the drag begins and to which the target will be moved (subject to constraints).

DragHandler can be used together with the Drag attached property to implement drag-and-drop.

See also Drag, MouseArea, and Qt Quick Examples - Pointer Handlers.

Property Documentation

The mouse buttons that can activate this DragHandler.

By default, this property is set to Qt.LeftButton. It can be set to an OR combination of mouse buttons, and will ignore events from other buttons.

For example, if a component (such as TextEdit) already handles left-button drags in its own way, it can be augmented with a DragHandler that does something different when dragged via the right button:

Rectangle { id: canvas width: 640 height: 480 color: "#333" property int highestZ: 0

[Repeater](qml-qtquick-repeater.html) {
    model: FolderListModel { nameFilters: ["*.qml"] }

    delegate: Rectangle {
        required property [string](qml-string.html) fileName
        required property [url](qml-url.html) fileUrl
        required property [int](qml-int.html) index

        id: frame
        x: index * 30; y: index * 30
        width: 320; height: 240
        property [bool](qml-bool.html) dragging: ldh.active || rdh.active
        onDraggingChanged: if (dragging) z = ++canvas.highestZ
        border { width: 2; color: dragging ? "red" : "steelblue" }
        color: "beige"
        clip: true

        [TextEdit](qml-qtquick-textedit.html) {
            // drag to select text
            id: textEdit
            textDocument.source: frame.fileUrl
            x: 3; y: 3

            BoundaryRule on y {
                id: ybr
                minimum: textEdit.parent.height - textEdit.height; maximum: 0
                minimumOvershoot: 200; maximumOvershoot: 200
                overshootFilter: BoundaryRule.Peak
            }
        }

        [DragHandler](qml-qtquick-draghandler.html) {
            id: rdh
            // right-drag to position the "window"
            acceptedButtons: Qt.RightButton
        }

        [WheelHandler](qml-qtquick-wheelhandler.html) {
            target: textEdit
            property: "y"
            onActiveChanged: if (!active) ybr.returnToBounds()
        }

        [Rectangle](qml-qtquick-rectangle.html) {
            anchors.right: parent.right
            width: titleText.implicitWidth + 12
            height: titleText.implicitHeight + 6
            border { width: 2; color: parent.border.color }
            bottomLeftRadius: 6
            [Text](qml-qtquick-text.html) {
                id: titleText
                color: "saddlebrown"
                anchors.centerIn: parent
                text: frame.fileName
                textFormat: Text.PlainText
            }
            [DragHandler](qml-qtquick-draghandler.html) {
                id: ldh
                // left-drag to position the "window"
                target: frame
            }
        }
    }
}

}

The types of pointing devices that can activate this DragHandler.

By default, this property is set to PointerDevice.AllDevices. If you set it to an OR combination of device types, it will ignore events from non-matching devices.

Note: Not all platforms are yet able to distinguish mouse and touchpad; and on those that do, you often want to make mouse and touchpad behavior the same.

acceptedModifiers : flags

If this property is set, it will require the given keyboard modifiers to be pressed in order to react to pointer events, and otherwise ignore them.

For example, two DragHandlers can perform two different drag-and-drop operations, depending on whether the Control modifier is pressed:

GridView { id: root width: 320 height: 480 cellWidth: 80 cellHeight: 80 interactive: false

displaced: Transition {
    [NumberAnimation](qml-qtquick-numberanimation.html) {
        properties: "x,y"
        easing.type: Easing.OutQuad
    }
}

model: DelegateModel {
    id: visualModel
    model: 24
    property [var](qml-var.html) dropTarget: undefined
    property [bool](qml-bool.html) copy: false
    delegate: DropArea {
        id: delegateRoot

        width: 80
        height: 80

        onEntered: drag => {
            if (visualModel.copy) {
                if (drag.source !== icon)
                    visualModel.dropTarget = icon
            } else {
                visualModel.items.move(drag.source.DelegateModel.itemsIndex, icon.DelegateModel.itemsIndex)
            }
        }

        [Rectangle](qml-qtquick-rectangle.html) {
            id: icon
            objectName: DelegateModel.itemsIndex

            property [string](qml-string.html) text
            Component.onCompleted: {
                color = Qt.rgba(0.2 + (48 - DelegateModel.itemsIndex) * Math.random() / 48,
                                0.3 + DelegateModel.itemsIndex * Math.random() / 48,
                                0.4 * Math.random(),
                                1.0)
                text = DelegateModel.itemsIndex
            }
            border.color: visualModel.dropTarget === this ? "black" : "transparent"
            border.width: 2
            radius: 3
            width: 72
            height: 72
            anchors {
                horizontalCenter: parent.horizontalCenter
                verticalCenter: parent.verticalCenter
            }

            states: [
                [State](qml-qtquick-state.html) {
                    when: dragHandler.active || controlDragHandler.active
                    [ParentChange](qml-qtquick-parentchange.html) {
                        target: icon
                        parent: root
                    }

                    [AnchorChanges](qml-qtquick-anchorchanges.html) {
                        target: icon
                        anchors {
                            horizontalCenter: undefined
                            verticalCenter: undefined
                        }
                    }
                }
            ]

            [Text](qml-qtquick-text.html) {
                anchors.centerIn: parent
                color: "white"
                font.pointSize: 14
                text: controlDragHandler.active ? "+" : icon.text
            }

            [DragHandler](qml-qtquick-draghandler.html) {
                id: dragHandler
                acceptedModifiers: Qt.NoModifier
                onActiveChanged: if (!active) visualModel.dropTarget = undefined
            }

            [DragHandler](qml-qtquick-draghandler.html) {
                id: controlDragHandler
                acceptedModifiers: Qt.ControlModifier
                onActiveChanged: {
                    visualModel.copy = active
                    if (!active) {
                        visualModel.dropTarget.text = icon.text
                        visualModel.dropTarget.color = icon.color
                        visualModel.dropTarget = undefined
                    }
                }
            }

            Drag.active: dragHandler.active || controlDragHandler.active
            Drag.source: icon
            Drag.hotSpot.x: 36
            Drag.hotSpot.y: 36
        }
    }
}

}

If this property is set to Qt.KeyboardModifierMask (the default value), then the DragHandler ignores the modifier keys.

If you set acceptedModifiers to an OR combination of modifier keys, it means all of those modifiers must be pressed to activate the handler.

The available modifiers are as follows:

Constant Description
NoModifier No modifier key is allowed.
ShiftModifier A Shift key on the keyboard must be pressed.
ControlModifier A Ctrl key on the keyboard must be pressed.
AltModifier An Alt key on the keyboard must be pressed.
MetaModifier A Meta key on the keyboard must be pressed.
KeypadModifier A keypad button must be pressed.
GroupSwitchModifier X11 only (unless activated on Windows by a command line argument). A Mode_switch key on the keyboard must be pressed.
KeyboardModifierMask The handler does not care which modifiers are pressed.

See also Qt::KeyboardModifier.

acceptedPointerTypes : flags

The types of pointing instruments (finger, stylus, eraser, etc.) that can activate this DragHandler.

By default, this property is set to PointerDevice.AllPointerTypes. If you set it to an OR combination of device types, it will ignore events from non-matching devices.

active : bool [read-only]

This holds true whenever this Input Handler has taken sole responsibility for handing one or more eventPoints, by successfully taking an exclusive grab of those points. This means that it is keeping its properties up-to-date according to the movements of those eventPoints and actively manipulating its target (if any).

activeTranslation : vector2d [read-only]

The translation while the drag gesture is being performed. It is 0, 0 when the gesture begins, and increases as the event point(s) are dragged downward and to the right. After the gesture ends, it stays the same; and when the next drag gesture begins, it is reset to 0, 0 again.

cursorShape : Qt::CursorShape

This property holds the cursor shape that will appear whenever the mouse is hovering over the parent item while active is true.

The available cursor shapes are:

The default value is not set, which allows the cursor of parent item to appear. This property can be reset to the same initial condition by setting it to undefined.

Note: When this property has not been set, or has been set to undefined, if you read the value it will return Qt.ArrowCursor.

See also Qt::CursorShape, QQuickItem::cursor(), and HoverHandler::cursorShape.

The distance in pixels that the user must drag an eventPoint in order to have it treated as a drag gesture.

The default value depends on the platform and screen resolution. It can be reset back to the default value by setting it to undefined. The behavior when a drag gesture begins varies in different handlers.

If a PointerHandler is disabled, it will reject all events and no signals will be emitted.

This property specifies the permissions when this handler's logic decides to take over the exclusive grab, or when it is asked to approve grab takeover or cancellation by another handler.

Constant Description
PointerHandler.TakeOverForbidden This handler neither takes from nor gives grab permission to any type of Item or Handler.
PointerHandler.CanTakeOverFromHandlersOfSameType This handler can take the exclusive grab from another handler of the same class.
PointerHandler.CanTakeOverFromHandlersOfDifferentType This handler can take the exclusive grab from any kind of handler.
PointerHandler.CanTakeOverFromItems This handler can take the exclusive grab from any type of Item.
PointerHandler.CanTakeOverFromAnything This handler can take the exclusive grab from any type of Item or Handler.
PointerHandler.ApprovesTakeOverByHandlersOfSameType This handler gives permission for another handler of the same class to take the grab.
PointerHandler.ApprovesTakeOverByHandlersOfDifferentType This handler gives permission for any kind of handler to take the grab.
PointerHandler.ApprovesTakeOverByItems This handler gives permission for any kind of Item to take the grab.
PointerHandler.ApprovesCancellation This handler will allow its grab to be set to null.
PointerHandler.ApprovesTakeOverByAnything This handler gives permission for any type of Item or Handler to take the grab.

The default is PointerHandler.CanTakeOverFromItems | PointerHandler.CanTakeOverFromHandlersOfDifferentType | PointerHandler.ApprovesTakeOverByAnything which allows most takeover scenarios but avoids e.g. two PinchHandlers fighting over the same touchpoints.

The margin beyond the bounds of the parent item within which an eventPoint can activate this handler. For example, you can make it easier to drag small items by allowing the user to drag from a position nearby:

Rectangle { width: 24 height: 24 border.color: "steelblue" Text { text: "it's\ntiny" font.pixelSize: 7 rotation: -45 anchors.centerIn: parent }

[DragHandler](qml-qtquick-draghandler.html) {
    margin: 12
}

}

The Item which is the scope of the handler; the Item in which it was declared. The handler will handle events on behalf of this Item, which means a pointer event is relevant if at least one of its eventPoints occurs within the Item's interior. Initially target() is the same, but it can be reassigned.

See also target and QObject::parent().

The translation to be applied to the target if it is not null. Otherwise, bindings can be used to do arbitrary things with this value. While the drag gesture is being performed, activeTranslation is continuously added to it; after the gesture ends, it stays the same.

This property holds the snap mode.

The snap mode configures snapping of the target item's center to the eventPoint.

Possible values:

Constant Description
DragHandler.NoSnap Never snap
DragHandler.SnapAuto The target snaps if the eventPoint was pressed outside of the target item and the target is a descendant of parent item (default)
DragHandler.SnapWhenPressedOutsideTarget The target snaps if the eventPoint was pressed outside of the target
DragHandler.SnapAlways Always snap

The Item which this handler will manipulate.

By default, it is the same as the parent, the Item within which the handler is declared. However, it can sometimes be useful to set the target to a different Item, in order to handle events within one item but manipulate another; or to null, to disable the default behavior and do something else instead.

xAxis group
xAxis.activeValue : real [read-only]
xAxis.enabled : bool
xAxis.maximum : real
xAxis.minimum : real

xAxis controls the constraints for horizontal dragging.

minimum is the minimum acceptable value of x to be applied to the target. maximum is the maximum acceptable value of x to be applied to the target. If enabled is true, horizontal dragging is allowed. activeValue is the same as activeTranslation.x.

The activeValueChanged signal is emitted when activeValue changes, to provide the increment by which it changed. This is intended for incrementally adjusting one property via multiple handlers.

yAxis group
yAxis.activeValue : real [read-only]
yAxis.enabled : bool
yAxis.maximum : real
yAxis.minimum : real

yAxis controls the constraints for vertical dragging.

minimum is the minimum acceptable value of y to be applied to the target. maximum is the maximum acceptable value of y to be applied to the target. If enabled is true, vertical dragging is allowed. activeValue is the same as activeTranslation.y.

The activeValueChanged signal is emitted when activeValue changes, to provide the increment by which it changed. This is intended for incrementally adjusting one property via multiple handlers:

import QtQuick

Rectangle { width: 50; height: 200

[Rectangle](qml-qtquick-rectangle.html) {
    id: knob
    width: parent.width; height: width; radius: width / 2
    anchors.centerIn: parent
    color: "lightsteelblue"

    [Rectangle](qml-qtquick-rectangle.html) {
        antialiasing: true
        width: 4; height: 20
        x: parent.width / 2 - 2
    }

    [WheelHandler](qml-qtquick-wheelhandler.html) {
        property: "rotation"
    }
}

[DragHandler](qml-qtquick-draghandler.html) {
    target: null
    dragThreshold: 0
    yAxis.onActiveValueChanged: (delta)=> { knob.rotation -= delta }
}

}

Signal Documentation

If this handler has already grabbed the given point, this signal is emitted when the grab is stolen by a different Pointer Handler or Item.

Note: The corresponding handler is onCanceled.

grabChanged(PointerDevice::GrabTransition transition, eventPoint point)

This signal is emitted when the grab has changed in some way which is relevant to this handler.

The transition (verb) tells what happened. The point (object) is the point that was grabbed or ungrabbed.

Valid values for transition are:

Constant Description
PointerDevice.GrabExclusive This handler has taken primary responsibility for handling the point.
PointerDevice.UngrabExclusive This handler has given up its previous exclusive grab.
PointerDevice.CancelGrabExclusive This handler's exclusive grab has been taken over or cancelled.
PointerDevice.GrabPassive This handler has acquired a passive grab, to monitor the point.
PointerDevice.UngrabPassive This handler has given up its previous passive grab.
PointerDevice.CancelGrabPassive This handler's previous passive grab has terminated abnormally.

Note: The corresponding handler is onGrabChanged.

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