WheelHandler QML Type
Handler for the mouse wheel. More...
Import Statement: | import QtQuick 2.14 |
Properties
- activeTimeout : real
- invertible : bool
- orientation : enum
- property : string
- rotation : real
- rotationScale : real
- targetScaleMultiplier : real
- targetTransformAroundCursor : bool
Detailed Description
WheelHandler is a handler that is used to interactively manipulate some numeric property of an Item as the user rotates the mouse wheel. Like other Input Handlers, by default it manipulates its target. Declare property to control which target property will be manipulated:
import QtQuick 2.14 Rectangle { width: 170; height: 120 color: "green"; antialiasing: true WheelHandler { property: "rotation" onWheel: console.log("rotation", event.angleDelta.y, "scaled", rotation, "@", point.position, "=>", parent.rotation) } }
BoundaryRule is quite useful in combination with WheelHandler (as well as with other Input Handlers) to declare the allowed range of values that the target property can have. For example it is possible to implement scrolling using a combination of WheelHandler and DragHandler to manipulate the scrollable Item's y property when the user rotates the wheel or drags the item on a touchscreen, and BoundaryRule to limit the range of motion from the top to the bottom:
import QtQuick 2.14 import Qt.labs.animation 1.0 Item { width: 320; height: 480 Flow { id: content width: parent.width spacing: 2; padding: 2 WheelHandler { orientation: Qt.Vertical property: "y" rotationScale: 15 acceptedDevices: PointerDevice.Mouse | PointerDevice.TouchPad onActiveChanged: if (!active) ybr.returnToBounds() } DragHandler { xAxis.enabled: false onActiveChanged: if (!active) ybr.returnToBounds() } BoundaryRule on y { id: ybr minimum: content.parent.height - content.height maximum: 0 minimumOvershoot: 400; maximumOvershoot: 400 overshootFilter: BoundaryRule.Peak } Repeater { model: 1000 Rectangle { color: "gray"; width: 10 + Math.random() * 100; height: 15 } } } }
Alternatively if targetProperty is not set or target is null, WheelHandler will not automatically manipulate anything; but the rotation property can be used in a binding to manipulate another property, or you can implement onWheel
and handle the wheel event directly.
WheelHandler handles only a rotating mouse wheel by default. Optionally it can handle smooth-scrolling events from touchpad gestures, by setting acceptedDevices to PointerDevice.Mouse | PointerDevice.TouchPad
.
Note: Some non-mouse hardware (such as a touch-sensitive Wacom tablet, or a Linux laptop touchpad) generates real wheel events from gestures. WheelHandler will respond to those events as wheel events regardless of the setting of the acceptedDevices property.
See also MouseArea and Flickable.
Property Documentation
activeTimeout : real |
The amount of time in seconds after which the active property will revert to false
if no more wheel events are received. The default is 0.1
(100 ms).
When WheelHandler handles events that contain scroll phase information, such as events from some touchpads, the active property will become false
as soon as an event with phase Qt::ScrollEnd is received; in that case the timeout is not necessary. But a conventional mouse with a wheel does not provide the scroll phase: the mouse cannot detect when the user has decided to stop scrolling, so the active property transitions to false
after this much time has elapsed.
invertible : bool |
Whether or not to reverse the direction of property change if QQuickPointerScrollEvent::inverted is true. The default is true
.
If the operating system has a "natural scrolling" setting that causes scrolling to be in the same direction as the finger movement, then if this property is set to true
, and WheelHandler is directly setting a property on target, the direction of movement will correspond to the system setting. If this property is set to false, it will invert the rotation so that the direction of motion is always the same as the direction of finger movement.
Which wheel to react to. The default is Qt.Vertical
.
Not every mouse has a Horizontal
wheel; sometimes it is emulated by tilting the wheel sideways. A touchpad can usually generate both vertical and horizontal wheel events.
property : string |
The property to be modified on the target when the mouse wheel is rotated.
The default is no property (empty string). When no target property is being automatically modified, you can use bindings to react to mouse wheel rotation in arbitrary ways.
You can use the mouse wheel to adjust any numeric property. For example if property
is set to x
, the target will move horizontally as the wheel is rotated. The following properties have special behavior:
Constant | Description |
---|---|
scale | scale will be modified in a non-linear fashion as described under targetScaleMultiplier. If targetTransformAroundCursor is true , the x and y properties will be simultaneously adjusted so that the user will effectively zoom into or out of the point under the mouse cursor. |
rotation | rotation will be set to rotation. If targetTransformAroundCursor is true , the l{QQuickItem::x}{x} and y properties will be simultaneously adjusted so that the user will effectively rotate the item around the point under the mouse cursor. |
The adjustment of the given target property is always scaled by rotationScale.
rotation : real |
The angle through which the mouse wheel has been rotated since the last time this property was set, in wheel degrees.
A positive value indicates that the wheel was rotated up/right; a negative value indicates that the wheel was rotated down/left.
A basic mouse click-wheel works in steps of 15 degrees.
The default is 0
at startup. It can be programmatically set to any value at any time. The value will be adjusted from there as the user rotates the mouse wheel.
See also orientation.
rotationScale : real |
targetScaleMultiplier : real |
The amount by which the target scale is to be multiplied whenever the rotation changes by 15 degrees. This is relevant only when property is "scale"
.
The scale
will be multiplied by targetScaleMultiplier
angleDelta * rotationScale / 15. The default is 2
1/3, which means that if rotationScale is left at its default value, and the mouse wheel is rotated by one "click" (15 degrees), the target will be scaled by approximately 1.25; after three "clicks" its size will be doubled or halved, depending on the direction that the wheel is rotated. If you want to make it double or halve with every 2 clicks of the wheel, set this to 2
1/2 (1.4142). If you want to make it scale the opposite way as the wheel is rotated, set rotationScale
to a negative value.
targetTransformAroundCursor : bool |
Whether the target should automatically be repositioned in such a way that it is transformed around the mouse cursor position while the property is adjusted. The default is true
.
If property is set to "rotation"
and targetTransformAroundCursor is true
, then as the wheel is rotated, the target item will rotate in place around the mouse cursor position. If targetTransformAroundCursor
is false
, it will rotate around its transformOrigin instead.