TapHandler QML Type

Handler for taps and clicks. More...

Import Statement: import Qt.labs.handlers 1.0
Inherits:

SinglePointHandler

Properties

Signals

Detailed Description

TapHandler is a handler for taps on a touchscreen or clicks on a mouse.

Detection of a valid tap gesture depends on gesturePolicy. Note that buttons (such as QPushButton) are often implemented not to care whether the press and release occur close together: if you press the button and then change your mind, you need to drag all the way off the edge of the button in order to cancel the click. Therefore the default gesturePolicy is TapHandler.ReleaseWithinBounds. If you want to require that the press and release are close together in both space and time, set it to TapHandler.DragThreshold.

For multi-tap gestures (double-tap, triple-tap etc.), the distance moved must not exceed QPlatformTheme::MouseDoubleClickDistance with mouse and QPlatformTheme::TouchDoubleTapDistance with touch, and the time between taps must not exceed QStyleHints::mouseDoubleClickInterval().

See also MouseArea.

Property Documentation

acceptedButtons : int

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")
    }
}

Note: Tapping on a touchscreen or tapping the stylus on a graphics tablet emulates clicking the left mouse button. This behavior can be altered via acceptedDevices or acceptedPointerTypes.


acceptedDevices : int

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

acceptedModifiers : int

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")
   }
}

acceptedPointerTypes : int

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 events.

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

[read-only] active : bool

This holds true whenever this PointerHandler 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 Event Points and actively manipulating its target (if any).


enabled : bool

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


gesturePolicy : enumeration

The spatial constraint for a tap or long press gesture to be recognized, in addition to the constraint that the release must occur before longPressThreshold has elapsed. If these constraints are not satisfied, the tapped signal is not emitted, and tapCount is not incremented. If the spatial constraint is violated, isPressed transitions immediately from true to false, regardless of the time held.

ConstantDescription
TapHandler.DragThresholdThe event point must not move significantly. If the mouse, finger or stylus moves past the system-wide drag threshold (QStyleHints::startDragDistance), the tap gesture is canceled, even if the button or finger is still pressed. This policy can be useful whenever TapHandler needs to cooperate with other pointer handlers (for example DragHandler), because in this case TapHandler will never grab.
TapHandler.WithinBoundsIf the event point leaves the bounds of the target item, the tap gesture is canceled. The TapHandler will grab on press, but release the grab as soon as the boundary constraint is no longer satisfied.
TapHandler.ReleaseWithinBounds(the default value) At the time of release (the mouse button is released or the finger is lifted), if the event point is outside the bounds of the target item, a tap gesture is not recognized. This is the default value, because it corresponds to typical button behavior: you can cancel a click by dragging outside the button, and you can also change your mind by dragging back inside the button before release. Note that it's necessary for TapHandler to grab on press and retain it until release (greedy grab) in order to detect this gesture.

grabPermission : bool

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


longPressThreshold : real

The time in seconds that an event point must be pressed in order to trigger a long press gesture and emit the longPressed() signal. If the point is released before this time limit, a tap can be detected if the gesturePolicy constraint is satisfied. The default value is QStyleHints::mousePressAndHoldInterval() converted to seconds.


[read-only] parent : Item

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 event points occurs within the Item's interior. Initially target() is the same, but target() can be reassigned.

See also QQuick::PointerHandler::target() and QObject::parent().


[read-only] point : HandlerPoint

The event point currently being handled. When no point is currently being handled, this object is reset to default values (all coordinates are 0).


[read-only] pressed : bool

Holds true whenever the mouse or touch point is pressed, and any movement since the press is compliant with the current gesturePolicy. When the event point is released or the policy is violated, pressed will change to false.


[read-only] tapCount : int

The number of taps which have occurred within the time and space constraints to be considered a single gesture. For example, to detect a double-tap, you can write:

Rectangle {
    width: 100; height: 30
    signal doubleTap
    TapHandler {
        acceptedButtons: Qt.AllButtons
        onTapped: if (tapCount == 2) doubleTap()
    }
}

target : Item

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.


[read-only] timeHeld : real

The amount of time in seconds that a pressed point has been held, without moving beyond the drag threshold. It will be updated at least once per frame rendered, which enables rendering an animation showing the progress towards an action which will be triggered by a long-press. It is also possible to trigger one of a series of actions depending on how long the press is held.

A value of less than zero means no point is being held within this handler's Item.


Signal Documentation

canceled(EventPoint point)

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.


grabChanged(EventPoint point)

This signal is emitted when this handler has acquired or relinquished a passive or exclusive grab of the given point.


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