[beginner] Displaying data from a class C++



  • Hi all,
    I'm trying to create a program that displays live data from a Myo armband. I have a class DataCollector that inherits from QObject and myo::DeviceListener which collects information from the band and updates some int variables, I then just want these variables to be displayed by separate LCDNumber components in a class GUItest that inherits from QMainWindow.

    What is the best way about this to go about this? I think I'm getting confused with the signals and slots.

    // This is a snippet of my code:

    public:
    int value() const { return emgMax; }

    public slots:
    void setMaxValue(int value)
    {
    if (value != emgMax){
    emgMax = value;
    emit valueChanged(value);
    }
    }

    signals:
    void valueChanged(int newValue);

    private:
    int emgMax;

    // this is the connection
    connect(&collector, &DataCollector::valueChanged, ui.lcdMax, SLOT(display(int)));

    // this is the call within dataCollector
    if (emgSum > emgMax)
    {
    setMaxValue(emgSum);
    }


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    // this looks wrong
    connect(&collector, &DataCollector::valueChanged, ui.lcdMax, SLOT(display(int)));
    
    connect(&collector, &DataCollector::valueChanged, ui.lcdMax, static_cast<void (QLCDNumber::*)(int)>(&QLCDNumber::display));
    

    However are you sure that collector lives long enough ?



  • Thank you for your response. The compiler likes your connect statement.

    But yes, I am now unsure about the collector's life. I have the collector as an uninitialized attribute in the class GUItest then in the constructor I handle the connection.

    Where is the program flow after "return a.exec();" is reached? is there away I can just have a loop and update the lcd displays every second? As the data being collected changes in the milliseconds


  • Lifetime Qt Champion

    You can use a QTimer if you want to update at a fixed interval


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