Drilldown饼状图

饼状图每一块下面还有一个饼状图。这里用QT官方的例子做个笔记。
QT += charts
基本思路：
1、新建一个类DrilldownSlice继承自QPieSlice类，
实现3个方法：

 - updateLabel()//设置标题内容
 - showHighlight(bool show)//是否显示数值可见和突出显示
 - drilldownSeries()返回构造函数里存储的对象

2、新建一个类DrilldownChart继承自QChart类，
实现1个方法：

handleSliceClicked(QPieSlice *slice)//一个槽，连接到每一块的点击信号，每次点击就会把块的QPieSlice 对象往里传递，并把QPieSlice 对象强制转换为DrilldownSlice（因为DrilldownSlice也是继承QPieSlice）；然后改变DrilldownChart里的数据内容；
changeSeries(QAbstractSeries *series)//把旧的QAbstractSeries 移除，把新的QAbstractSeries 赋值给当前QAbstractSeries ，并加到DrilldownChart中，更改名字。

3、新建1个QPieSeries对象，往里加N个DrilldownSlice对象，其中的一个参数为QPieSeries对象，而QPieSeries对象有包含有N个DrilldownSlice和N个QPieSeries对象。

4、把每一个QPieSeries对象的clicked信号连接到DrilldownChart的槽handleSliceClicked，这样就能实现每次点击都能到handleSliceClicked函数里边改变QChart的数据内容了。

drilldownchart.h文件

#ifndef DRILLDOWNCHART_H
#define DRILLDOWNCHART_H

#include <QtCharts/QChart>

QT_CHARTS_BEGIN_NAMESPACE
class QAbstractSeries;
class QPieSlice;
QT_CHARTS_END_NAMESPACE

QT_CHARTS_USE_NAMESPACE

class DrilldownChart : public QChart
{
    Q_OBJECT
public:
    explicit DrilldownChart(QGraphicsItem *parent = 0, Qt::WindowFlags wFlags = 0);
    ~DrilldownChart();
    void changeSeries(QAbstractSeries *series);

public Q_SLOTS:
    void handleSliceClicked(QPieSlice *slice);

private:
    QAbstractSeries *m_currentSeries;
};

#endif // DRILLDOWNCHART_H

drilldownchart.c文件

#include "drilldownchart.h"
#include "drilldownslice.h"

QT_CHARTS_USE_NAMESPACE

DrilldownChart::DrilldownChart(QGraphicsItem *parent, Qt::WindowFlags wFlags)
    : QChart(QChart::ChartTypeCartesian, parent, wFlags),
      m_currentSeries(0)
{

}

DrilldownChart::~DrilldownChart()
{

}

void DrilldownChart::changeSeries(QAbstractSeries *series)
{
    // NOTE: if the series is owned by the chart it will be deleted
    // here the "window" owns the series...
    if (m_currentSeries)
        removeSeries(m_currentSeries);
    m_currentSeries = series;
    addSeries(series);
    setTitle(series->name());
}

void DrilldownChart::handleSliceClicked(QPieSlice *slice)
{
    DrilldownSlice *drilldownSlice = static_cast<DrilldownSlice *>(slice);
    changeSeries(drilldownSlice->drilldownSeries());
}

#include "moc_drilldownchart.cpp"

drilldownslice.h文件

#ifndef DRILLDOWNSLICE_H
#define DRILLDOWNSLICE_H

#include <QtCharts/QPieSlice>

QT_CHARTS_BEGIN_NAMESPACE
class QAbstractSeries;
QT_CHARTS_END_NAMESPACE

QT_CHARTS_USE_NAMESPACE

class DrilldownSlice : public QPieSlice
{
    Q_OBJECT

public:
    DrilldownSlice(qreal value, QString prefix, QAbstractSeries *drilldownSeries);
    virtual ~DrilldownSlice();
    QAbstractSeries *drilldownSeries() const;

public Q_SLOTS:
    void updateLabel();
    void showHighlight(bool show);

private:
    QAbstractSeries *m_drilldownSeries;
    QString m_prefix;
};

#endif // DRILLDOWNSLICE_H

drilldownslice.c文件

#include "drilldownslice.h"

QT_CHARTS_USE_NAMESPACE

DrilldownSlice::DrilldownSlice(qreal value, QString prefix, QAbstractSeries *drilldownSeries)
    : m_drilldownSeries(drilldownSeries),
      m_prefix(prefix)
{
    setValue(value);
    updateLabel();
    setLabelFont(QFont("Arial", 8));
    connect(this, &DrilldownSlice::percentageChanged, this, &DrilldownSlice::updateLabel);
    connect(this, &DrilldownSlice::hovered, this, &DrilldownSlice::showHighlight);
}

DrilldownSlice::~DrilldownSlice()
{

}

QAbstractSeries *DrilldownSlice::drilldownSeries() const
{
    return m_drilldownSeries;
}

void DrilldownSlice::updateLabel()
{
    QString label = m_prefix;
    label += " $";
    label += QString::number(this->value());
    label += ", ";
    label += QString::number(this->percentage() * 100, 'f', 1);
    label += "%";
    setLabel(label);
}

void DrilldownSlice::showHighlight(bool show)
{
    setLabelVisible(show);
    setExploded(show);
}

#include "moc_drilldownslice.cpp"

main.cpp文件

#include "drilldownchart.h"
#include "drilldownslice.h"
#include <QtWidgets/QApplication>
#include <QtWidgets/QMainWindow>
#include <QtCore/QRandomGenerator>
#include <QtCharts/QChartView>
#include <QtCharts/QLegend>
#include <QtCharts/QPieSeries>

QT_CHARTS_USE_NAMESPACE

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QMainWindow window;

    DrilldownChart *chart = new DrilldownChart();
    chart->setTheme(QChart::ChartThemeLight);
    chart->setAnimationOptions(QChart::AllAnimations);
    chart->legend()->setVisible(true);
    chart->legend()->setAlignment(Qt::AlignRight);

    QPieSeries *yearSeries = new QPieSeries(&window);
    yearSeries->setName("Sales by year - All");

    const QStringList months = {
        "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
    };
    const QStringList names = {
        "Jane", "John", "Axel", "Mary", "Susan", "Bob"
    };

    for (const QString &name : names) {
        QPieSeries *series = new QPieSeries(&window);
        series->setName("Sales by month - " + name);

        for (const QString &month : months)
            *series << new DrilldownSlice(QRandomGenerator::global()->bounded(1000), month, yearSeries);

        QObject::connect(series, &QPieSeries::clicked, chart, &DrilldownChart::handleSliceClicked);

        *yearSeries << new DrilldownSlice(series->sum(), name, series);
    }

    QObject::connect(yearSeries, &QPieSeries::clicked, chart, &DrilldownChart::handleSliceClicked);

    chart->changeSeries(yearSeries);

    QChartView *chartView = new QChartView(chart);
    chartView->setRenderHint(QPainter::Antialiasing);
    window.setCentralWidget(chartView);
    window.resize(800, 500);
    window.show();

    return a.exec();
}