Qt Quick 输入处理程序

Qt Quick Input Handlers are a set of QML types used to handle events from keyboard, touch, mouse, and stylus devices in a UI. In contrast to event-handling items, such as MouseArea and Flickable , input handlers are explicitly non-visual, require less memory and are intended to be used in greater numbers: one handler instance per aspect of interaction. Each input handler instance handles certain events on behalf of its parent Item. Thus the visual and behavioral concerns are better separated, and the behavior is built up by finer-grained composition.

The pre-existing 键 attached property is similar in concept, so we refer to the pointing-device-oriented handlers plus 键 together as the set of Input Handlers. We expect to offer more attached-property use cases in future versions of Qt.

输入处理程序

DragHandler	Handler for dragging
HoverHandler	Handler for mouse and tablet hover
KeyNavigation	Supports key navigation by arrow keys
键	Provides key handling to Items
PinchHandler	Handler for pinch gestures
PointHandler	Handler for reacting to a single touchpoint
TapHandler	Handler for taps and clicks
WheelHandler	Handler for the mouse wheel

关键特征

一些关键特征：

Handle keystrokes within the focused Item
Handle gestures such as tapping or dragging regardless which device it comes from
Handle gestures from different classes of devices in different ways
Each Item can have unlimited Handlers

处理程序操纵项

Some Handlers add interactivity simply by being declared inside an Item:

import QtQuick 2.12
Rectangle {
    width: 100
    height: 100
    color: "lightsteelblue"
    DragHandler { }
}

处理程序特性和信号

All Handlers have properties that can be used in bindings, and signals that can be handled to react to input:

import QtQuick 2.12
Rectangle {
    id: button
    signal clicked
    width: 150; height: 50; radius: 3
    color: tapHandler.pressed ? "goldenrod" : hoverHandler.hovered ? "wheat" : "beige"
    border.color: activeFocus ? "brown" : "transparent"
    focus: true
    HoverHandler {
        id: hoverHandler
    }
    TapHandler {
        id: tapHandler
        onTapped: button.clicked()
    }
    Keys.onEnterPressed: button.clicked()
}

指针抓取

An important concept with Pointer Handlers is the type of grabs that they perform. The only kind of grab an Item can take is the exclusive grab: for example if you call QPointerEvent::setExclusiveGrabber (), the following mouse moves and mouse release event will be sent only to that object. (As a workaround to this exclusivity, see QQuickItem::setFiltersChildMouseEvents () 和 QQuickItem::childMouseEventFilter ().) However Pointer Handlers have an additional mechanism available: the passive grab . Mouse and touch press events are delivered by visiting all the Items in top-down Z order: first each Item's child Handlers, and then the Item itself. At the time a press event is delivered, a Handler can take either a passive or an exclusive grab depending on its needs. If it takes a passive grab, it is guaranteed to receive the updates and the release, even if other Items or Handlers in the scene take any kind of grab, passive or exclusve. Some Handlers (such as PointHandler ) can work only with passive grabs; others require exclusive grabs; and others can "lurk" with passive grabs until they detect that a gesture is being performed, and then make the transition from passive to exclusive grab.

When a grab transition is requested, PointerHandler::grabPermissions , QQuickItem::keepMouseGrab () 和 QQuickItem::keepTouchGrab () control whether the transition will be allowed.

Qt Quick

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