Handler for reacting to a single touchpoint. 更多...
| import 语句： | import QtQuick |
| 继承： | SinglePointHandler |
PointHandler can be used to show feedback about a touchpoint or the mouse position, or to otherwise react to pointer events.
When a press event occurs, each instance of PointHandler chooses a single point which is not yet "taken" at that moment: if the press occurs within the bounds of the
PointerHandler::parent
, and no sibling PointHandler within the same
PointerHandler::parent
has yet acquired a passive grab on that point, and if the other constraints such as
acceptedButtons
,
acceptedDevices
etc. are satisfied, it's eligible, and the PointHandler then acquires a passive grab. In this way, the
PointerHandler::parent
acts like an exclusive group: there can be multiple instances of PointHandler, and the set of pressed touchpoints will be distributed among them. Each PointHandler which has chosen a point to track has its
active
property
true
. It then continues to track its chosen point until release: the properties of the
point
will be kept up-to-date. Any Item can bind to these properties, and thereby follow the point's movements.
By being only a passive grabber, it has the ability to keep independent oversight of all movements. The passive grab cannot be stolen or overridden even when other gestures are detected and exclusive grabs occur.
If your goal is orthogonal surveillance of eventpoints, an older alternative was QObject::installEventFilter (), but that has never been a built-in QtQuick feature: it requires some C++ code, such as a QQuickItem subclass. PointHandler is more efficient than that, because only pointer events will be delivered to it, during the course of normal event delivery in QQuickWindow ; whereas an event filter needs to filter all QEvents of all types, and thus sets itself up as a potential event delivery bottleneck.
One possible use case is to add this handler to a transparent Item which is on top of the rest of the scene (by having a high z value), so that when a point is freshly pressed, it will be delivered to that Item and its handlers first, providing the opportunity to take the passive grab as early as possible. Such an item (like a pane of glass over the whole UI) can be a convenient parent for other Items which visualize the kind of reactive feedback which must always be on top; and likewise it can be the parent for popups, popovers, dialogs and so on. If it will be used in that way, it can be helpful for your main.cpp to use QQmlContext::setContextProperty () to make the "glass pane" accessible by ID to the entire UI, so that other Items and PointHandlers can be reparented to it.
import QtQuick Window { width: 480 height: 320 visible: true Item { id: glassPane z: 10000 anchors.fill: parent PointHandler { id: handler acceptedDevices: PointerDevice.TouchScreen | PointerDevice.TouchPad target: Rectangle { parent: glassPane color: "red" visible: handler.active x: handler.point.position.x - width / 2 y: handler.point.position.y - height / 2 width: 20; height: width; radius: width / 2 } } } }
Like all input handlers, a PointHandler has a
target
property, which may be used as a convenient place to put a point-tracking Item; but PointHandler will not automatically manipulate the
target
item in any way. You need to use bindings to make it react to the
point
.
注意： On macOS, PointHandler does not react to multiple fingers on the trackpad by default, although it does react to a pressed point (mouse position). That is because macOS can provide either native gesture recognition, or raw touchpoints, but not both. We prefer to use the native gesture event in PinchHandler , so we do not want to disable it by enabling touch. However MultiPointTouchArea does enable touch, thus disabling native gesture recognition within the entire window; so it's an alternative if you only want to react to all the touchpoints but do not require the smooth native-gesture experience.
另请参阅 MultiPointTouchArea , HoverHandler ，和 Pointer Handlers Example .
|
acceptedButtons : flags |
The mouse buttons that can activate this PointHandler .
默认情况下，此特性被设为 Qt.LeftButton . It can be set to an OR combination of mouse buttons, and will ignore events in which other buttons are pressed or held.
import QtQuick Item { width: 480; height: 320 Rectangle { color: handler.active ? "tomato" : "wheat" x: handler.point.position.x - width / 2 y: handler.point.position.y - height / 2 width: 20; height: width; radius: width / 2 } PointHandler { id: handler acceptedButtons: Qt.MiddleButton | Qt.RightButton } }
注意： On a touchscreen, there are no buttons, so this property does not prevent PointHandler from reacting to touchpoints.
|
acceptedDevices : flags |
The types of pointing devices that can activate this PointHandler .
默认情况下，此特性被设为 PointerDevice.AllDevices . If you set it to an OR combination of device types, it will ignore events from non-matching devices :
PointHandler { id: handler acceptedDevices: PointerDevice.TouchScreen | PointerDevice.TouchPad target: Rectangle { parent: glassPane color: "red" visible: handler.active x: handler.point.position.x - width / 2 y: handler.point.position.y - height / 2 width: 20; height: width; radius: width / 2 } }
|
acceptedModifiers : flags |
If this property is set, PointHandler requires the given keyboard modifiers to be pressed in order to react to PointerEvents , and otherwise ignores them.
If this property is set to
Qt.KeyboardModifierMask
(the default value), then
PointHandler
ignores the modifier keys.
For example, an Item could have two handlers, one of which is enabled only if the required keyboard modifier is pressed:
import QtQuick Item { id: feedbackPane width: 480; height: 320 PointHandler { id: control acceptedModifiers: Qt.ControlModifier cursorShape: Qt.PointingHandCursor target: Rectangle { parent: feedbackPane color: control.active ? "indianred" : "khaki" x: control.point.position.x - width / 2 y: control.point.position.y - height / 2 width: 20; height: width; radius: width / 2 } } PointHandler { id: shift acceptedModifiers: Qt.ShiftModifier | Qt.MetaModifier cursorShape: Qt.CrossCursor target: Rectangle { parent: feedbackPane color: shift.active ? "darkslateblue" : "lightseagreen" x: shift.point.position.x - width / 2 y: shift.point.position.y - height / 2 width: 30; height: width; radius: width / 2 } } }
若设置
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:
| 常量 | 描述 |
|---|---|
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. |
另请参阅 Qt::KeyboardModifier .
|
acceptedPointerTypes : flags |
The types of pointing instruments (finger, stylus, eraser, etc.) that can activate this PointHandler .
默认情况下，此特性被设为 PointerDevice.AllPointerTypes . If you set it to an OR combination of device types, it will ignore events from non-matching devices :
import QtQuick Canvas { id: canvas width: 800 height: 600 antialiasing: true renderTarget: Canvas.FramebufferObject property var points: [] onPaint: { if (points.length < 2) return var ctx = canvas.getContext('2d'); ctx.save() ctx.strokeStyle = stylusHandler.active ? "blue" : "white" ctx.lineCap = "round" ctx.beginPath() ctx.moveTo(points[0].x, points[0].y) for (var i = 1; i < points.length; i++) ctx.lineTo(points[i].x, points[i].y) ctx.lineWidth = 3 ctx.stroke() points = points.slice(points.length - 2, 1) ctx.restore() } PointHandler { id: stylusHandler acceptedPointerTypes: PointerDevice.Pen onPointChanged: { canvas.points.push(point.position) canvas.requestPaint() } } PointHandler { id: eraserHandler acceptedPointerTypes: PointerDevice.Eraser onPointChanged: { canvas.points.push(point.position) canvas.requestPaint() } } Rectangle { width: 10; height: 10 color: stylusHandler.active ? "green" : eraserHandler.active ? "red" : "beige" } }
The Pointer Handlers Example includes a more complex example for drawing on a Canvas with a graphics tablet.
|
[read-only] active : bool |
This holds
true
whenever the constraints are satisfied and this
PointHandler
is reacting. This means that it is keeping its properties up-to-date according to the movements of the
eventPoints
that satisfy the constraints.
|
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.
注意：
When this property has not been set, or has been set to
undefined
, if you read the value it will return
Qt.ArrowCursor
.
另请参阅 Qt::CursorShape , QQuickItem::cursor ()，和 HoverHandler::cursorShape .
|
enabled : bool |
若 PointerHandler is disabled, it will reject all events and no signals will be emitted.
|
grabPermissions : flags |
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.
| 常量 | 描述 |
|---|---|
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. |
默认为
PointerHandler.CanTakeOverFromItems | PointerHandler.CanTakeOverFromHandlersOfDifferentType | PointerHandler.ApprovesTakeOverByAnything
which allows most takeover scenarios but avoids e.g. two PinchHandlers fighting over the same touchpoints.
|
margin : real |
The margin beyond the bounds of the parent item within which an eventPoint can activate this handler.
默认值为
0
.
import QtQuick Item { width: 480; height: 320 Rectangle { anchors.fill: handlingContainer anchors.margins: -handler.margin color: "beige" } Rectangle { id: handlingContainer width: 200; height: 200 anchors.centerIn: parent border.color: "green" color: handler.active ? "lightsteelblue" : "khaki" Text { text: "X" x: handler.point.position.x - width / 2 y: handler.point.position.y - height / 2 visible: handler.active } PointHandler { id: handler margin: 30 } } }
|
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 eventPoints occurs within the Item's interior. Initially target() is the same, but it can be reassigned.
注意：
When a handler is declared in a
QtQuick3D.Model
object, the parent is not an Item, therefore this property is
null
.
另请参阅 target and QObject::parent ().
|
[read-only] point : handlerPoint |
The eventPoint currently being handled. When no point is currently being handled, this object is reset to default values (all coordinates are 0).
|
target : real |
A property that can conveniently hold an Item to be manipulated or to show feedback. Unlike other
Pointer Handlers
,
PointHandler
does not do anything with the
target
on its own: you usually need to create reactive bindings to properties such as
SinglePointHandler::point
and
PointHandler::active
. If you declare an Item instance here, you need to explicitly set its
parent
，因为
PointHandler
is not an Item.
By default, it is the same as the parent , the Item within which the handler is declared.
|
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.
注意：
相应处理程序是
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.
注意：
相应处理程序是
onGrabChanged
.
