使用QCPDataSelection来设置选中的区域，并将QCPGraph的可选择区域设置成QCP::stMultipleDataRanges

void AreaPieces::initCustomPlot(QCustomPlot *parentPlot)
{
    QVector<double> x = {
            0, 1, 2, 3, 4, 5, 6, 7, 8
    };
    QVector<double> y = {
            200, 560, 750, 580, 250, 300, 450, 300, 100,
    };

    QVector<QString> labels = {
            "2019-10-10",
            "2019-10-11",
            "2019-10-12",
            "2019-10-13",
            "2019-10-14",
            "2019-10-15",
            "2019-10-16",
            "2019-10-17",
            "2019-10-18",
    };
    auto ticker = QSharedPointer<QCPAxisTickerText>::create();
    ticker->setTicks(x, labels);

    QCPDataSelection selection;
    selection.addDataRange(QCPDataRange(1, 4));
    selection.addDataRange(QCPDataRange(5, 8));

    QPen pen(QColor("#5470C6"), 5);
    auto graph = new QCPSmoothGraph(parentPlot->xAxis, parentPlot->yAxis);
    parentPlot->graph()->setData(x, y);
    parentPlot->graph()->setPen(pen);
    parentPlot->graph()->selectionDecorator()->setBrush(QColor(0, 0, 180, 102));
    parentPlot->graph()->selectionDecorator()->setPen(pen);
    parentPlot->graph()->setSelectable(QCP::stMultipleDataRanges);
    parentPlot->graph()->setSelection(selection);

    parentPlot->xAxis->setTicker(ticker);
    parentPlot->xAxis->grid()->setVisible(false);
    parentPlot->yAxis->setRange(0, 1000);
    parentPlot->xAxis->setRange(0, 8);
}