将 lambda 函数作为第三个参数传递给 QObject::connect 时出错

Question

我正在尝试通过将 lambda 函数作为第三个参数传递来调用 QObject::connect。

但是，我 Visual Visual Studio 给了我以下错误：

在 0x0000000066B48265 (Qt5Cored.dll) 中未处理的异常 QCustomPlotInVS_FirstTry.exe：0xC0000005：读取访问冲突 位置 0x0000000000000008。

这是发生错误时调用堆栈上的前 3 行：

Qt5Cored.dll!QListData::size() 第 91 行
QCustomPlotInVS_FirstTry.exe!QList::size() 第 132 行 QCustomPlotInVS_FirstTry.exe!QCustomPlot::graph(int index) 第 9657 行

qList.h 中的第 91 行是： inline int size() const { return d->end - d->begin; }

我认为我收到此错误是因为我错误地尝试将指针（即QCustomPlot* plot）与 lambda 函数一起使用。

我的 lambda 函数语法是否正确？ 如果没有，我做错了什么？

这是我用 lambda 函数调用 QObject::connect 的函数：

void setupRealTimePlot(QCustomPlot* plot, QTimer* dataTimer)
{
    plot->addGraph(); // blue line
    plot->graph(0)->setPen(QPen(Qt::blue));
    plot->graph(0)->setBrush(QBrush(QColor(240, 255, 200)));
    plot->graph(0)->setAntialiasedFill(false);
    plot->addGraph(); // red line
    plot->graph(1)->setPen(QPen(Qt::red));
    plot->graph(0)->setChannelFillGraph(plot->graph(1));

    plot->addGraph(); // blue dot
    plot->graph(2)->setPen(QPen(Qt::blue));
    plot->graph(2)->setLineStyle(QCPGraph::lsNone);
    plot->graph(2)->setScatterStyle(QCPScatterStyle::ssDisc);
    plot->addGraph(); // red dot
    plot->graph(3)->setPen(QPen(Qt::red));
    plot->graph(3)->setLineStyle(QCPGraph::lsNone);
    plot->graph(3)->setScatterStyle(QCPScatterStyle::ssDisc);

    plot->xAxis->setTickLabelType(QCPAxis::ltDateTime);
    plot->xAxis->setDateTimeFormat("hh:mm:ss");
    plot->xAxis->setAutoTickStep(false);
    plot->xAxis->setTickStep(2);
    plot->axisRect()->setupFullAxesBox();

    // make left and bottom axes transfer their ranges to right and top axes:
    QObject::connect(plot->xAxis, SIGNAL(rangeChanged(QCPRange)), plot->xAxis2, SLOT(setRange(QCPRange)));
    QObject::connect(plot->yAxis, SIGNAL(rangeChanged(QCPRange)), plot->yAxis2, SLOT(setRange(QCPRange)));

    // setup a timer that repeatedly calls MainWindow::realtimeDataSlot:
    QObject::connect(dataTimer, &QTimer::timeout, 
        [&]()
        {
            // calculate two new data points:
            double key = QDateTime::currentDateTime().toMSecsSinceEpoch()/1000.0;
            static double lastPointKey = 0;
            if (key-lastPointKey > 0.01) // at most add point every 10 ms
            {
            double value0 = qSin(key); //qSin(key*1.6+qCos(key*1.7)*2)*10 + qSin(key*1.2+0.56)*20 + 26;
            double value1 = qCos(key); //qSin(key*1.3+qCos(key*1.2)*1.2)*7 + qSin(key*0.9+0.26)*24 + 26;
            // add data to lines:
            plot->graph(0)->addData(key, value0);
            plot->graph(1)->addData(key, value1);
            // set data of dots:
            plot->graph(2)->clearData();
            plot->graph(2)->addData(key, value0);
            plot->graph(3)->clearData();
            plot->graph(3)->addData(key, value1);
            // remove data of lines that's outside visible range:
            plot->graph(0)->removeDataBefore(key-8);
            plot->graph(1)->removeDataBefore(key-8);
            // rescale value (vertical) axis to fit the current data:
            plot->graph(0)->rescaleValueAxis();
            plot->graph(1)->rescaleValueAxis(true);
            lastPointKey = key;
            }
            // make key axis range scroll with the data (at a constant range size of 8):
            plot->xAxis->setRange(key+0.25, 8, Qt::AlignRight);
            plot->replot();

            // calculate frames per second:
            static double lastFpsKey;
            static int frameCount;
            ++frameCount;
            if (key-lastFpsKey > 2) // average fps over 2 seconds
            {
            lastFpsKey = key;
            frameCount = 0;
            }
        });

    dataTimer->start(0); // Interval 0 means to refresh as fast as possible

}

Answer 1

您在稍后调用的闭包中通过引用（初犯：plot）捕获堆栈分配的变量；一旦你的闭包被调用，所有这些东西都会变成垃圾。而是按值捕获。