DragHandler QML Type

The mouse buttons which can activate this Pointer Handler.

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, a control could be made to respond to left and right clicks in different ways, with two handlers:

 Item {
     TapHandler {
         onTapped: console.log("left clicked")
     }
     TapHandler {
         acceptedButtons: Qt.RightButton
         onTapped: console.log("right clicked")
     }
 }

The types of pointing devices that can activate this Pointer Handler.

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.

For example, a control could be made to respond to mouse and stylus clicks in one way, and touchscreen taps in another way, with two handlers:

 Item {
    TapHandler {
        acceptedDevices: PointerDevice.Mouse | PointerDevice.TouchPad | PointerDevice.Stylus
        onTapped: console.log("clicked")
    }
    TapHandler {
        acceptedDevices: PointerDevice.TouchScreen
        onTapped: console.log("tapped")
    }
 }

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.

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

For example, an Item could have two handlers of the same type, one of which is enabled only if the required keyboard modifiers are pressed:

 Item {
    TapHandler {
        acceptedModifiers: Qt.ControlModifier
        onTapped: console.log("control-tapped")
    }
    TapHandler {
        acceptedModifiers: Qt.NoModifier
        onTapped: console.log("tapped")
    }
 }

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

 Item {
    TapHandler {
        acceptedModifiers: Qt.ControlModifier | Qt.AltModifier | Qt.ShiftModifier
        onTapped: console.log("control-alt-shift-tapped")
    }
 }

The available modifiers are as follows:

If you need even more complex behavior than can be achieved with combinations of multiple handlers with multiple modifier flags, you can check the modifiers in JavaScript code:

 Item {
     TapHandler {
         onTapped:
             switch (point.modifiers) {
             case Qt.ControlModifier | Qt.AltModifier:
                 console.log("CTRL+ALT");
                 break;
             case Qt.ControlModifier | Qt.AltModifier | Qt.MetaModifier:
                 console.log("CTRL+META+ALT");
                 break;
             default:
                 console.log("other modifiers", point.modifiers);
                 break;
             }
     }
 }

See also Qt::KeyboardModifier.

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

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.

For example, a control could be made to respond to mouse, touch, and stylus clicks in some way, but delete itself if tapped with an eraser tool on a graphics tablet, with two handlers:

 Rectangle {
    id: rect
    TapHandler {
        acceptedPointerTypes: PointerDevice.Generic | PointerDevice.Finger | PointerDevice.Pen
        onTapped: console.log("clicked")
    }
    TapHandler {
        acceptedPointerTypes: PointerDevice.Eraser
        onTapped: rect.destroy()
    }
 }

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).

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.

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:

• Qt.ArrowCursor
• Qt.UpArrowCursor
• Qt.CrossCursor
• Qt.WaitCursor
• Qt.IBeamCursor
• Qt.SizeVerCursor
• Qt.SizeHorCursor
• Qt.SizeBDiagCursor
• Qt.SizeFDiagCursor
• Qt.SizeAllCursor
• Qt.BlankCursor
• Qt.SplitVCursor
• Qt.SplitHCursor
• Qt.PointingHandCursor
• Qt.ForbiddenCursor
• Qt.WhatsThisCursor
• Qt.BusyCursor
• Qt.OpenHandCursor
• Qt.ClosedHandCursor
• Qt.DragCopyCursor
• Qt.DragMoveCursor
• Qt.DragLinkCursor

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.

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.

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, on a PinchHandler where the target is also the parent, it's useful to set this to a distance at least half the width of a typical user's finger, so that if the parent has been scaled down to a very small size, the pinch gesture is still possible. Or, if a TapHandler-based button is placed near the screen edge, it can be used to comply with Fitts's Law: react to mouse clicks at the screen edge even though the button is visually spaced away from the edge by a few pixels.

The default value is 0.

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:

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 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 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 {
         id: knob
         width: parent.width; height: width; radius: width / 2
         anchors.centerIn: parent
         color: "lightsteelblue"

         Rectangle {
             antialiasing: true
             width: 4; height: 20
             x: parent.width / 2 - 2
         }

         WheelHandler {
             property: "rotation"
         }
     }

     DragHandler {
         target: null
         dragThreshold: 0
         yAxis.onActiveValueChanged: (delta)=> { knob.rotation -= delta }
     }
 }

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.

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: