如何防止QChartView放大为负x或y轴值

Question

我希望防止将QChartView放大到负x或y轴值。因此，我试图在我的子类mouseReleaseEvent中拦截QChartView，然后在执行缩放之前修改rubberBandRect的坐标。但是在鼠标释放后，rubberBandRect坐标似乎总是为零，所以我认为我没有使用正确的rubberBandRect。

我试图根据QChartView的文档进行调整(重点是添加的)：

void：：mouseReleaseEvent(QMouseEvent * event )如果释放鼠标左键并启用橡皮筋，则事件事件被接受，视图被放大到由橡皮筋指定的矩形中。

当我尝试查看下面代码片段中的rubberBandRect中的实际值时，无论我如何缩放光标，矩形的x/y和高度/宽度值总是为零。

我也看了这个问题的答案：Qt How to connect the rubberBandChanged signal，但在这种情况下，他们想要的行为在主窗口，这不是我想要的。谢谢!

class MyQChartView : public QtCharts::QChartView
{
    Q_OBJECT
public:
    MyQChartView(QWidget *parent = 0);
    //...
protected:
    void mouseReleaseEvent(QMouseEvent *event);
    void keyPressEvent(QKeyEvent *event);

};


void MyQChartView::mouseReleaseEvent(QMouseEvent *event)
{
    
    //always shows zeroes for the x and y position
    if(event->button() == Qt::LeftButton){
        std::cout << "x: " << this->rubberBandRect().x() << " y: " << this->rubberBandRect().y() << std::endl;
        
        QChartView::mouseReleaseEvent(event);
    }
    
    //any other event
    QChartView::mouseReleaseEvent(event);
}

Answer 1

经过大量的实验，我想我找到了最好的解决办法。必须做一个rubberband指针，然后findChild才能到达实际的橡皮筋。然后，鼠标释放后，我得到了图的面积坐标以及橡皮筋坐标。然后我做了一个包围盒(bounded_geometry)，如果橡皮筋出了界，就限制它的值。然后我zoomIn到有界的几何图形框。仅仅修改橡皮筋是行不通的，因为这些坐标不是浮点，舍入误差会导致缩放错误。

class MyQChartView : public QtCharts::QChartView
{
    Q_OBJECT
public:
    MyQChartView(QWidget *parent = 0):
    QChartView(parent)
    {
        myChart = new QtCharts::QChart();
        setRubberBand(QtCharts::QChartView::RectangleRubberBand);
        rubberBandPtr = this->findChild<QRubberBand *>();
        this->setChart(myChart);
        //...other things
    }
    //...
protected:
    void mouseReleaseEvent(QMouseEvent *event);
    void keyPressEvent(QKeyEvent *event);
private:
    QRubberBand * rubberBandPtr;
    QtCharts::QChart * myChart;
};


void MyQChartView::mouseReleaseEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton){
        //first get the plot area and save the needed values (could change each time)
        QRectF plotArea = myChart->plotArea();
        qreal xbound = plotArea.x(); //values < xbound are out of bounds on x axis
        qreal ybound = plotArea.y() + plotArea.height(); // !!! note that values > ybound are out of bounds (i.e. negative y values)
        
        QPointF rb_tl = rubberBandPtr->geometry().topLeft();
        QPointF rb_br = rubberBandPtr->geometry().bottomRight();
        
        QRectF bounded_geometry = rubberBandPtr->geometry();
        
        if(rb_tl.x() < xbound){
            bounded_geometry.setX(xbound);
        }
        if(rb_br.y() > ybound){ //note that values > ybound are out of bounds
            bounded_geometry.setBottom(ybound);
        }
        
        myChart->zoomIn(bounded_geometry);        
        rubberBandPtr->close();

        return;
    }
    
    //any other event
    QChartView::mouseReleaseEvent(event);
}