PinchHandler QML Type

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 property is true when all the constraints (epecially minimumPointCount and maximumPointCount) are satisfied and the target, if any, is being manipulated.

The rotation of the pinch gesture in degrees, with positive values clockwise. It is 0 when the gesture begins. If target is not null, this will be automatically added to its rotation. Otherwise, bindings can be used to do arbitrary things with this value.

See also QtQuick::PinchHandler::rotationAxis.activeValue.

The scale factor while the pinch gesture is being performed. It is 1.0 when the gesture begins, increases as the touchpoints are spread apart, and decreases as the touchpoints are brought together. If target is not null, its scale will be automatically multiplied by this value. Otherwise, bindings can be used to do arbitrary things with this value.

See also QtQuick::PinchHandler::scaleAxis.activeValue.

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

A point exactly in the middle of the currently-pressed touch points. The target will be rotated around this point.

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 rotation 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 pinch gesture is being performed, activeRotation is continuously added; after the gesture ends, it stays the same; and when the next pinch gesture begins, it begins to be modified by activeRotation again.

It's possible to set this property, as a way of synchronizing the basis rotation with a rotation that was set in some other way, for example by another handler. If you set this property directly, activeRotation does not change, and rotationChanged(0) is emitted.

The scale factor that will automatically be set on the target if it is not null. Otherwise, bindings can be used to do arbitrary things with this value. While the pinch gesture is being performed, it is continuously multiplied by activeScale; after the gesture ends, it stays the same; and when the next pinch gesture begins, it begins to be multiplied by activeScale again.

It's possible to set this property, as a way of synchronizing the basis scale with a scale that was set in some other way, for example by another handler. If you set this property directly, activeScale does not change, and scaleChanged(1) is emitted.

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 pinch gesture is being performed, activeTranslation is continuously added to it; after the gesture ends, it stays the same.

It's possible to set this property, as a way of synchronizing the basis translation with a translation that was set in some other way, for example by another handler. If you set this property directly, activeTranslation does not change, and translationChanged({0, 0}) is emitted.

rotationAxis controls the constraints for setting the rotation of the target item according to the rotation of the group of touchpoints.

minimum is the minimum acceptable rotation. maximum is the maximum acceptable rotation. If enabled is true, rotation is allowed. activeValue is the same as QtQuick::PinchHandler::activeRotation.

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: 100; height: 100
     color: "lightsteelblue"; antialiasing: true

     PinchHandler {
         id: handler
         target: null
         xAxis.onActiveValueChanged: (delta) => parent.radius -= delta
         yAxis.onActiveValueChanged: (delta) => parent.border.width += delta
         rotationAxis.onActiveValueChanged: (delta) => parent.rotation += delta // add
         scaleAxis.onActiveValueChanged: (delta) => parent.scale *= delta // multiply
     }

     WheelHandler {
         acceptedModifiers: Qt.NoModifier
         property: "rotation"
     }

     WheelHandler {
         acceptedModifiers: Qt.ControlModifier
         property: "scale"
     }
 }

scaleAxis controls the constraints for setting the scale of the target item according to the distance between the touchpoints.

minimum is the minimum acceptable scale. maximum is the maximum acceptable scale. If enabled is true, scaling is allowed. activeValue is the same as QtQuick::PinchHandler::activeScale.

The activeValueChanged signal is emitted when activeValue changes, to provide the multiplier for the incremental change. This is intended for incrementally adjusting one property via multiple handlers.

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"; antialiasing: true

     PinchHandler {
         id: handler
         target: null
         xAxis.onActiveValueChanged: (delta) => parent.radius -= delta
         yAxis.onActiveValueChanged: (delta) => parent.border.width += delta
         rotationAxis.onActiveValueChanged: (delta) => parent.rotation += delta // add
         scaleAxis.onActiveValueChanged: (delta) => parent.scale *= delta // multiply
     }

     WheelHandler {
         acceptedModifiers: Qt.NoModifier
         property: "rotation"
     }

     WheelHandler {
         acceptedModifiers: Qt.ControlModifier
         property: "scale"
     }
 }

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 translation of the target item.

minimum is the minimum acceptable x coordinate of the translation. maximum is the maximum acceptable x coordinate of the translation. If enabled is true, horizontal dragging is allowed.

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: 100; height: 100
     color: "lightsteelblue"; antialiasing: true

     PinchHandler {
         id: handler
         target: null
         xAxis.onActiveValueChanged: (delta) => parent.radius -= delta
         yAxis.onActiveValueChanged: (delta) => parent.border.width += delta
         rotationAxis.onActiveValueChanged: (delta) => parent.rotation += delta // add
         scaleAxis.onActiveValueChanged: (delta) => parent.scale *= delta // multiply
     }

     WheelHandler {
         acceptedModifiers: Qt.NoModifier
         property: "rotation"
     }

     WheelHandler {
         acceptedModifiers: Qt.ControlModifier
         property: "scale"
     }
 }

yAxis controls the constraints for vertical translation of the target item.

minimum is the minimum acceptable y coordinate of the translation. maximum is the maximum acceptable y coordinate of the translation. If enabled is true, vertical dragging is allowed.

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: 100; height: 100
     color: "lightsteelblue"; antialiasing: true

     PinchHandler {
         id: handler
         target: null
         xAxis.onActiveValueChanged: (delta) => parent.radius -= delta
         yAxis.onActiveValueChanged: (delta) => parent.border.width += delta
         rotationAxis.onActiveValueChanged: (delta) => parent.rotation += delta // add
         scaleAxis.onActiveValueChanged: (delta) => parent.scale *= delta // multiply
     }

     WheelHandler {
         acceptedModifiers: Qt.NoModifier
         property: "rotation"
     }

     WheelHandler {
         acceptedModifiers: Qt.ControlModifier
         property: "scale"
     }
 }

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:

The rotationChanged signal is emitted when activeRotation (and therefore persistentRotation) changes. The delta value gives the additive change in rotation. For example, if the user moves fingers to change the pinch distance so that activeRotation changes from 10 to 30 degrees, rotationChanged(20) will be emitted. You can use that to incrementally change the rotation of an item:

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"

     PinchHandler {
         id: handler
         target: null
         onRotationChanged: (delta) => parent.rotation += delta // add
         onScaleChanged: (delta) => parent.scale *= delta // multiply
     }
 }

The scaleChanged signal is emitted when activeScale (and therefore persistentScale) changes. The delta value gives the multiplicative change in scale. For example, if the user moves fingers to change the pinch distance so that activeScale changes from 2 to 2.5, scaleChanged(1.25) will be emitted. You can use that to incrementally change the scale of an item:

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"

     PinchHandler {
         id: handler
         target: null
         onRotationChanged: (delta) => parent.rotation += delta // add
         onScaleChanged: (delta) => parent.scale *= delta // multiply
     }
 }

The translationChanged signal is emitted when activeTranslation (and therefore persistentTranslation) changes. The delta vector gives the change in translation. You can use that to incrementally change the position of an item:

 import QtQuick

 Window {
     width: 320; height: 240
     visible: true
     title: handler.persistentRotation.toFixed(1) + "° " +
            handler.persistentTranslation.x.toFixed(1) + ", " +
            handler.persistentTranslation.y.toFixed(1) + " " +
            (handler.persistentScale * 100).toFixed(1) + "%"

     PinchHandler {
         id: handler
         target: null
         persistentScale: 0.25
         onTranslationChanged: (delta) => {
             image.x -= delta.x
             image.y -= delta.y
         }
     }

     Image {
         id: image
         source: "images/album-cover.jpg"
         scale: handler.persistentScale
         x: -600; y: -450
     }
 }