如何在線程中更新QCustomPlot數據？

Question

我想在c ++中顯示QCustomPlot的實時數據。 所以我這樣做：

在頭文件中：

class QtGuiApplication : public QMainWindow
{
Q_OBJECT

public:
QtGuiApplication(QWidget *parent = Q_NULLPTR);


private:
Ui::QtGuiApplicationClass ui;

//plot
QCustomPlot*        plot_;
std::thread thread_Displayer_;
bool thread_run_flag_ = false;
void thread_Displayer_fn();

};

在源文件中，我使用按鈕啟動線程，並...像這樣：

void     QtGuiApplication::btn_Display_clicked()
{

if (thread_run_flag_)
{
    ui.btn_Dispaly->setText("Display");
    thread_run_flag_ = false;
    if (thread_Displayer_.joinable())
    {
        thread_Displayer_.join();
    }
}
else
{
    thread_run_flag_ = false;
    if (thread_Displayer_.joinable())
    {
        thread_Displayer_.join();
    }
    ui.btn_Dispaly->setText("Stop");
    thread_run_flag_ = true;
    thread_Displayer_ = std::thread(&QtGuiApplication::thread_Displayer_fn, 
      this);
}


}

void     QtGuiApplication::thread_Displayer_fn()
{
double y_max_ = 0;
double y_min_ = 0;
while (thread_run_flag_)
{
    QVector<double> x(16384), y(16384); 
    for (int i = 0; i<16384; ++i)
    {
        x[i] = i; 
        y[i] = x[i]; 
        if (y[i] > y_max_)
            y_max_ = y[i];
        if (y[i] < y_min_)
            y_min_ = y[i];
    }

    plot_->yAxis->setRange(y_min_, y_max_);
    plot_->graph(0)->setData(x, y);
    plot_->replot();

   }

  }

但是當我啟動代碼時會發生此錯誤：

“無法將事件發送到其他線程擁有的對象”

我該如何解決？

Answer 1

您需要（或者至少這就是它的工作方式）創建一個信號，該信號將在線程中的for循環的每次迭代中發出。 然后，將此信號連接到將實際更新數據的插槽

class QtGuiApplication : public QWidget
{
    Q_OBJECT

public:
    explicit QtGuiApplication(QWidget *parent = 0);
    ~QtGuiApplication();
private slots:
    void setPlotData(QVector<double> x,QVector<double> y);
    void pushButtonClicked();
signals:
    void newData(QVector<double> x, QVector<double> y);
private:
    Ui::QtGuiApplication *ui;
    QCustomPlot* plot_;
    std::thread thread_Displayer_;
    bool thread_run_flag_ = false;
    void thread_Displayer_fn();
};

double fRand(double fMin, double fMax){
    double f = (double)rand() / RAND_MAX;
    return fMin + f * (fMax - fMin);
}

QtGuiApplication::QtGuiApplication(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::QtGuiApplication)
{
    // Set up UI
    ui->setupUi(this);
    plot_ = ui->qcustomplot;

    // Register data type for signals
    qRegisterMetaType<QVector<double>>("QVector<double>");

    // Prepare graph
    plot_->addGraph();

    // Connect
    connect(ui->pushButton,SIGNAL(clicked()),this,SLOT(pushButtonClicked()));
    connect(this,SIGNAL(newData(QVector<double>,QVector<double>)),this,SLOT(setPlotData(QVector<double>,QVector<double>)));
}

QtGuiApplication::~QtGuiApplication()
{
    delete ui;
}

void QtGuiApplication::pushButtonClicked()
{
    if (thread_run_flag_)
    {
        ui->pushButton->setText("Display");
        thread_run_flag_ = false;
        if (thread_Displayer_.joinable())
        {
            thread_Displayer_.join();
        }
    }
    else
    {
        thread_run_flag_ = false;
        if (thread_Displayer_.joinable())
        {
            thread_Displayer_.join();
        }
        ui->pushButton->setText("Stop");
        thread_run_flag_ = true;
        thread_Displayer_ = std::thread(&QtGuiApplication::thread_Displayer_fn,
          this);
    }
}

void QtGuiApplication::setPlotData(QVector<double> x, QVector<double> y)
{
    plot_->graph(0)->setData(x, y);
    plot_->rescaleAxes();
    plot_->replot();
}

void QtGuiApplication::thread_Displayer_fn()
{
    while (thread_run_flag_)
    {
        QVector<double> x(ui->spinBox->value()), y(ui->spinBox->value());
        for (int i = 0; i<ui->spinBox->value(); ++i)
        {
            x[i] = i;
            y[i] = fRand(0,10);
        }
        emit newData(x,y);
        usleep(ui->doubleSpinBox->value()*1000);// convert to us
    }
}

請注意，我在發射后還添加了usleep函數。 如果您不放置它，您將無法再次按下該按鈕並停止，我認為這是因為數據發送的速率很高。

在這里您可以找到整個示例。

Answer 2

使此函數靜態並嘗試void QtGuiApplication::thread_Displayer_fn()

  static void QtGuiApplication::thread_Displayer_fn()

因為從類QtGuiApplication創建的對象已經由主線程擁有，並且您正在嘗試使用上述語句從另一個線程（子線程）中調用該對象的方法。