Run a method from a C++ program with Qt without writing entire program in Qt [closed]

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Is it possible to run a certain method from a C++ program with Qt with certain input parameters when for instance a button is clicked without writing the complete program in Qt itself?

Let's say that I have a project in Visual Studio with a corresponding .exe and I want to run the method example with input parameter 5 whenever a button is clicked. How could I do that?

Answer 1

Qt operates by creating a QWidget window, and then an event loop.

Your code to create a window, and then a button that triggers another function is trivial.

Many of the examples Qt provides show this functionality.

To get started, Download Qt. Download the Qt Add-On for Visual Studio. Note, that the express edition of visual studio doesn't work with the Qt Add-On.

After you have all that done, create a Qt project from the Qt classes that are available. In this case, I would not choose QML/Qt Quick, but just a Qt Widgets class, such as QWidget or QDialog or QMainWindow.

Using the Qt Add-On should ensure that you have the libraries found and available to Visual Studio.

Make sure that you can get a Hello World example is buildable and running using a Qt Widget of some sort.

The code it generates for you should look like this:

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

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

    return a.exec();
}

To add in a button, you need to place it on a Widget and then connect a SLOT to its clicked() signal. The following is a compact way to do it.

#include <QWidget>
#include <QPushButton>
#include <QVBoxLayout>
#include <QDebug>
#include <QApplication>

static void someFunction ()
{
    qDebug() << "Button was clicked";
    // run my other function that requires a parameter of 5

    qDebug() << "Run my other function with 5!";
    // otherFunction(5);
}

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

    QPushButton *button = new QPushButton("Click Me");
    QObject::connect(button, &QPushButton::clicked, someFunction);

    QVBoxLayout *vbox = new QVBoxLayout();
    vbox->addWidget(button);

    w.setLayout(vbox);
    w.show();

    return a.exec();
}

To make a powerful GUI, you will want to leverage more than just a functor, and use QObjects and let it use the moc compiler and create your own signals and slots for all your custom functions.

Connecting to a functor is new with Qt 5.

http://qt-project.org/wiki/New_Signal_Slot_Syntax

http://woboq.com/blog/new-signals-slots-syntax-in-qt5.html

A more verbose way to do it, but allows for more expandability and OOP, is to subclass QWidget or QMainWindow, like it generated for you, and put a method in your subclassed function that you put under your slots list in your header file.

http://qt-project.org/doc/qt-5/signalsandslots.html

Take the time to understand signals and slots and you can create almost any GUI you can imagine using Qt. Good luck.

Hope that helps.