for (int i = 0;i < ui->plot->graph(0)->dataCount();i++) {
      float x = ui->plot->graph(0)->data()->at(i)->key;
      float y = ui->plot->graph(0)->data()->at(i)->value;
      qDebug() << x << y << endl;
}

connect(ui->plot, SIGNAL(mouseMove(QMouseEvent*)), this, SLOT(myMoveEvent(QMouseEvent*)));

void MainWindow::myMoveEvent(QMouseEvent *event) {
    //获取鼠标坐标，相对父窗体坐标
    int x_pos = event->pos().x();
    int y_pos = event->pos().y();

    //鼠标坐标转化为CustomPlot内部坐标
    float x_val = ui->plot->xAxis->pixelToCoord(x_pos);
    float y_val = ui->plot->yAxis->pixelToCoord(y_pos);

    QString str,strToolTip;
    str = QString::number(x_val, 10, 3);
    strToolTip += "x: ";
    strToolTip += str;
    strToolTip += "\n";

    for (int i = 0;i < ui->plot->xAxis->graphs().count();i++) {
        //获得x轴坐标位置对应的曲线上y的值
        float y = ui->plot->graph(i)->data()->at(x_val)->value;
        str = QString::number(y);
        strToolTip += "y" + QString::number(i) + "：";
        strToolTip += str;
        strToolTip += "\n";
    }
    QToolTip::showText(cursor().pos(), strToolTip, ui->plot);
}