Qt示例解析 【图表应用一】Legend

目的：介绍Qt中图表可以达到的一些效果，可以把我们的项目做的高大上。

此博文主要介绍图表说明Legend的一些设置，来源示例Legend和LegendMarker，位于\Examples\Qt-5.9.4\charts\

Legend主要实现对图表说明的编辑，添加删除Bar，图表说明的位置，以及图表说明字体的设置

LegendMarker主要实现图表说明与图表的对应关系，点击图表说明可以显示/隐藏相应的图表，上面图中隐藏了line1和line3

1. 放置位置

附着图表 m_chart->legend()->attachToChart();

不附着图表 m_chart->legend()->detachFromChart();

         位于图表上方 m_chart->legend()->setAlignment(Qt::AlignTop);

         位于图表下方 m_chart->legend()->setAlignment(Qt::AlignBottom);

         位于图表左侧 m_chart->legend()->setAlignment(Qt::AlignLeft);

         位于图表右侧 m_chart->legend()->setAlignment(Qt::AlignRight);

2. 设置字体

QFont font = m_chart->legend()->font();
font.setBold(!font.bold());//是否加粗
font.setItalic(!font.italic());//是否斜体
font.setPointSizeF(m_fontSize->value());//设置字体大小
m_chart->legend()->setFont(font);

3. 附着图表时设置边框

m_chart->legend()->setGeometry(QRectF(x,y,width,height));
m_chart->legend()->update();

4. 关联图表说明与图表

实现效果：点击图表说明时，相应的图表被显示或隐藏。

建立信号QLegendMarker::clicked-槽handleMarkerClicked关系

    const auto markers = m_chart->legend()->markers();
    for (QLegendMarker *marker : markers) {
        // Disconnect possible existing connection to avoid multiple connections
        QObject::disconnect(marker, &QLegendMarker::clicked,
                            this, &MainWidget::handleMarkerClicked);
        QObject::connect(marker, &QLegendMarker::clicked, this, &MainWidget::handleMarkerClicked);
    }

槽函数handleMarkerClicked实现

void handleMarkerClicked()
{
    //通过关联机制获取当前点击的LegendMarker
    QLegendMarker* marker = qobject_cast (sender());
    Q_ASSERT(marker);//若LegendMarker为空，则退出

    switch (marker->type())
    {
        //LegendMarkerType有以下几种情况：
        //LegendMarkerTypeXY表示line,spline,scatter的LegendMarker
        //LegendMarkerTypeArea表示area的LegendMarker
        //LegendMarkerTypeBar表示bar柱状图的LegendMarker
        //LegendMarkerTypePie表示pie饼状图的LegendMarker
        //LegendMarkerTypeBoxPlot表示盒形图的LegendMarker
        //LegendMarkerTypeCandlestick表示蜡烛图的LegendMarker
        case QLegendMarker::LegendMarkerTypeXY:
        {

        marker->series()->setVisible(!marker->series()->isVisible());

        // Turn legend marker back to visible, since hiding series also hides the marker
        // and we don't want it to happen now.
        marker->setVisible(true);

        // Dim the marker, if series is not visible
        qreal alpha = 1.0;

        if (!marker->series()->isVisible())
            alpha = 0.5;

        QColor color;
        QBrush brush = marker->labelBrush();
        color = brush.color();
        color.setAlphaF(alpha);
        brush.setColor(color);
        marker->setLabelBrush(brush);

        brush = marker->brush();
        color = brush.color();
        color.setAlphaF(alpha);
        brush.setColor(color);
        marker->setBrush(brush);

        QPen pen = marker->pen();
        color = pen.color();
        color.setAlphaF(alpha);
        pen.setColor(color);
        marker->setPen(pen);

        break;
        }
    default:
        {
        qDebug() << "Unknown marker type";
        break;
        }
    }
}