QML防止鼠标事件被过滤（窃取）

分手后的思念是犯贱 2023-02-20 06:31 25阅读 0赞

如果将 MouseArea 放置在筛选 child 鼠标事件的 Item（例如 Flickable、SwipeView ）中，则当父 Item 识别出手势（例如滑动）时，鼠标事件可能会从 MouseArea 中被过滤。如果将 preventStealing 属性设置为 true，则任何 Item 都不会窃取该 MouseArea 的鼠标事件。（注意，一旦某 Item 开始窃取事件，将 preventStealing 设置为 true 后，直到下一次相关事件才生效）

这个属性是 MouseArea 的，那么对于我们自定义的 C++ QQuickItem 该如何处理呢？通过 Qt 源码，可以看到是调用 QQuickItem 的 setKeepMouseGrab 函数进行设置（配合 setAcceptedMouseButtons(Qt::LeftButton) 启用了鼠标事件才有效）。

相关 Qt 源码：

//MouseArea

bool QQuickMouseArea::preventStealing() const
    {
        Q_D(const QQuickMouseArea);
        return d->preventStealing;
    }
    
    void QQuickMouseArea::setPreventStealing(bool prevent)
    {
        Q_D(QQuickMouseArea);
        if (prevent != d->preventStealing) {
            d->preventStealing = prevent;
            setKeepMouseGrab(d->preventStealing && d->enabled);
            emit preventStealingChanged();
        }
    }

//Flickable

bool QQuickFlickable::filterMouseEvent(QQuickItem *receiver, QMouseEvent *event)
    {
        Q_D(QQuickFlickable);
        QPointF localPos = mapFromScene(event->windowPos());
    
        Q_ASSERT_X(receiver != this, "", "Flickable received a filter event for itself");
        if (receiver == this && d->stealMouse) {
            // we are already the grabber and we do want the mouse event to ourselves.
            return true;
        }
    
        bool receiverDisabled = receiver && !receiver->isEnabled();
        bool stealThisEvent = d->stealMouse;
        bool receiverKeepsGrab = receiver && (receiver->keepMouseGrab() || receiver->keepTouchGrab());
        if ((stealThisEvent || contains(localPos)) && (!receiver || !receiverKeepsGrab || receiverDisabled)) {
            QScopedPointer<QMouseEvent> mouseEvent(QQuickWindowPrivate::cloneMouseEvent(event, &localPos));
            mouseEvent->setAccepted(false);
    
            switch (mouseEvent->type()) {
            case QEvent::MouseMove:
                d->handleMouseMoveEvent(mouseEvent.data());
                break;
            case QEvent::MouseButtonPress:
                d->handleMousePressEvent(mouseEvent.data());
                d->captureDelayedPress(receiver, event);
                stealThisEvent = d->stealMouse;   // Update stealThisEvent in case changed by function call above
                break;
            case QEvent::MouseButtonRelease:
                d->handleMouseReleaseEvent(mouseEvent.data());
                stealThisEvent = d->stealMouse;
                break;
            default:
                break;
            }
            if ((receiver && stealThisEvent && !receiverKeepsGrab && receiver != this) || receiverDisabled) {
                d->clearDelayedPress();
                grabMouse();
            } else if (d->delayedPressEvent) {
                grabMouse();
            }
    
            const bool filtered = stealThisEvent || d->delayedPressEvent || receiverDisabled;
            if (filtered) {
                event->setAccepted(true);
            }
            return filtered;
        } else if (d->lastPosTime != -1) {
            d->lastPosTime = -1;
            returnToBounds();
        }
        if (event->type() == QEvent::MouseButtonRelease || (receiverKeepsGrab && !receiverDisabled)) {
            // mouse released, or another item has claimed the grab
            d->lastPosTime = -1;
            d->clearDelayedPress();
            d->stealMouse = false;
            d->pressed = false;
        }
        return false;
    }

参考 Qt 文档：[https://doc.qt.io/qt-5/qml-qtquick-mousearea.html][https_doc.qt.io_qt-5_qml-qtquick-mousearea.html]

参考 Qt 源码：E:\\Qt\\qt-everywhere-src-5.15.0\\qtdeclarative\\src\\quick\\items\\qquickmousearea\_p.h

[https_doc.qt.io_qt-5_qml-qtquick-mousearea.html]: https://doc.qt.io/qt-5/qml-qtquick-mousearea.html#preventStealing-prop