Qt触摸屏双指缩放和单指移动界面（支持嵌入式设备）

本文介绍的QGraphicsView的双指缩放，QWidget更简单，可以参考当前内容。

1、首先需要打开触摸屏功能。

this->setAttribute(Qt::WA_AcceptTouchEvents);

2、在event事件管理器中接收触摸屏的三个事件，TouchBegin、TouchUpdate和TouchEnd。

3、判断单点触摸还是多点触摸。

4、如果多点触摸，通过比较前后两次两点间触摸位置来判断是放大还是缩小。

5、多点触摸时，会存在抖动情况，需要做防抖处理。

6、如果是单点触摸，通过比较手指放上去的位置和手指拖动时的位置来设置界面滚动条的位置。

代码：

属性设置

clike 复制代码

    this->setAttribute(Qt::WA_AcceptTouchEvents);

缩放和移动逻辑

clike 复制代码

bool MGraaphicsView::event(QEvent *e)
{
    static int index = 0;
    switch (e->type()) {
    case QEvent::TouchBegin:
    case QEvent::TouchUpdate:
    case QEvent::TouchEnd:
    {
        qDebug() <<"CProjectionPicture::event"<<e->type();
        QTouchEvent *touchEvent = static_cast<QTouchEvent *>(e);
        QList<QTouchEvent::TouchPoint> touchPoints = touchEvent->touchPoints();
        if (touchPoints.count() == 2) {
            //缩放
            const QTouchEvent::TouchPoint &touchPoint0 = touchPoints.first();
            const QTouchEvent::TouchPoint &touchPoint1 = touchPoints.last();
            qreal currentScaleFactor = QLineF(touchPoint0.pos(), touchPoint1.pos()).length()
                    / QLineF(touchPoint0.startPos(), touchPoint1.startPos()).length();
            if (currentScaleFactor  > _lastScaleFactor)
                index++;
            else if (currentScaleFactor  < _lastScaleFactor)
                index--;
            if (index == 5)//超过5次放大，则认为有效.防抖操作
            {
                index = 0;
                zoomOnce(true);
            }
            else if (index == -5)
            {
                index = 0;
                zoomOnce(false);
            }
            qDebug()<<index<<currentScaleFactor<<_lastScaleFactor;
            _lastScaleFactor = currentScaleFactor;
            update();
        }
        else if (touchPoints.count() == 1)
        {//移动
            const QTouchEvent::TouchPoint &touchPoint = touchPoints.first();
            if (e->type() == QEvent::TouchBegin || e->type() == QEvent::TouchEnd)
                _startScenePos = mapToScene(touchPoint.pos().toPoint());

            if (e->type() == QEvent::TouchUpdate)
            {
                QPointF endScenePos = mapToScene(touchPoint.pos().toPoint());
                QPointF delta = endScenePos - _startScenePos;
                int oposx = this->horizontalScrollBar()->value();
                int oposy = this->verticalScrollBar()->value();
                int nposx = oposx - delta.x();
                int nposy = oposy - delta.y();
                this->horizontalScrollBar()->setValue(nposx);
                this->verticalScrollBar()->setValue(nposy);
            }

            qDebug()<<"====="<<_startScenePos<<touchPoint.pos();
        }
        if (touchEvent->touchPointStates() & Qt::TouchPointReleased)
        {
            qDebug()<<"Qt::TouchPointReleased";
        }
        return true;//一定不要调QGraphicsView::event(e);否则手指触摸会经常失效
    }
    default:
        break;
    }

    return QGraphicsView::event(e);
}

//缩放

clike 复制代码

void MGraaphicsView::zoomOnce(bool increase)
{
    if (increase)
        setZoom(1);
    else
        setZoom(-1);
}

void MGraaphicsView::setZoom(int val)
{
    if (val > 0)
    {
        m_zoom++;
        auto scaleValue = qPow(2, m_zoom);
        setTransform(QTransform::fromScale(scaleValue, scaleValue));
    }
    else
    {
        m_zoom--;
        auto scaleValue = qPow(2, m_zoom);
        setTransform(QTransform::fromScale(scaleValue, scaleValue));
    }
}