Question

I’m new to C++ and I’m just start to port a program that was originally in python/Qt to C++/Qt in order to take advantage of a better terminal widget that I can embed in my program. Right now I’m a bit stuck, I’m trying to setup where if a different item from a drop-down box is selected the currentIndex() of a tab widget is changed accordingly.

Heres my code so far:

    //main.cpp

    #include <QApplication>
    #include "mainwindow.h"

    int main(int argc, char *argv[])
    {
        QApplication a(argc, argv);
        MainWindow w;
        w.show();

        return a.exec();
    }

heres the mainwindow.h

    #ifndef MAINWINDOW_H
    #define MAINWINDOW_H

    #include <QMainWindow>
    #include <QTimer>


    namespace Ui {
    class MainWindow;
    }

    class MainWindow : public QMainWindow
    {
        Q_OBJECT

    public:
        explicit MainWindow(QWidget *parent = 0);
        ~MainWindow();
        QTimer *timer;
        void startMyTimer()
        {
            timer = new QTimer();
            timer->setInterval(1);
            timer->start();
            QObject::connect(timer,SIGNAL(timeout()),this,SLOT(changeIndex()));
        }

    private:
        Ui::MainWindow *ui;
        void changeIndex();
         };

    #endif // MAINWINDOW_H

And lastly heres the mainwindow.cpp

    #include "mainwindow.h"
    #include "ui_mainwindow.h"

    MainWindow::MainWindow(QWidget *parent) :
        QMainWindow(parent),
        ui(new Ui::MainWindow)
    {
        ui->setupUi(this);
        changeIndex();
    }

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

    void MainWindow::changeIndex()
    {
        if (ui->comboBox->currentText() == "add-apt-repository")
        {
            ui->stackedWidget->setCurrentIndex(0);
            ui->checkBox->setCheckState(Qt::Checked);
        }
        if (ui->comboBox->currentText() == "apt-get")
        {
            ui->stackedWidget->setCurrentIndex(1);
            ui->checkBox->setCheckState(Qt::Checked);
        }
        if (ui->comboBox->currentText() == "aptitude")
        {
           ui->stackedWidget->setCurrentIndex(2);
           ui->checkBox->setCheckState(Qt::Checked);
        }
        if (ui->comboBox->currentText() == "bzr")
        {
            ui->stackedWidget->setCurrentIndex(3);
            ui->checkBox->setCheckState(Qt::Unchecked);
        }
        if (ui->comboBox->currentText() == "cd")
        {
            ui->stackedWidget->setCurrentIndex(4);
            ui->checkBox->setCheckState(Qt::Unchecked);
        }
        if (ui->comboBox->currentText() == "chmod")
        {
            ui->stackedWidget->setCurrentIndex(5);
            ui->checkBox->setCheckState(Qt::Checked);
        }
    }

I’ve looked at a bunch of QTimer examples but I’m at a loss.
I also tried doing if (ui->comboBox->changeEvent()) but I was probably using that wrong as well.

Answer 1

First, you probably have to mark changeIndex() as a slot, like this:

class MainWindow : public QMainWindow
{
    Q_OBJECT

    // ...

    private slots: 
        void changeIndex();

    private:
        Ui::MainWindow *ui;
}

This also requires you to invoke the Qt meta object compiler. If you use qmake, that’s already done for you. Otherwise, it depends on your build system.

Second, is there any particular reason for using the timer? You can also connect to one of the combo box’s currentIndexChanged signals.