Modify a QLabel with a QSlider

Meugiwara

Hello !

I'm started to use Qt and I did some programs to test many things like a QSlider which is moving a QProgressBar or a button to open a file (by example). However, I wanted to try something else, but I don't succeed.

I want to write a program with a QLabel and a QSlider in a QWidget. In the QLabel, there is written "I am X years old !" and the X is an int that can be changed by the QSlider. By example, if I move the QSlider to 50, there is written "I am 50 years old !" etc ...

Is there someone to help me with a simple function to do this ?

raven-worx

@Meugiwara

void onSliderValueChangedSlot(int value)
{
    label->setText( QString("I am %1 years old").arg(value);
}

connect this slot to the sliders valueChanged signal.

Meugiwara

If I don't use class, how can I add your code in the main function ?

/* Référence à un fichier include */
#include "main.h"

/* Fonction principale pour les essais */
int     main(int argc, char **argv)
{
    /* Exécuter un programme Qt */
    QApplication    program(argc, argv);
    /* Inscrire une fenêtre dans le programme Qt */
    QWidget         window;
    /* Mise en page intérieure des widgets de façon verticale */
    QVBoxLayout     layout;
    /* Les boutons "Open" et "Close" */
    QPushButton     obutton("Open");
    QPushButton     cbutton("Close");
    /* Le fichier désiré à ouvrir */
    QString         file;
    /* Le widget slider */
    QSlider         slider;
    /* La barre de progression */
    QProgressBar    bar;
    /* La phrase */
    QLabel          label;

    /* Titre de la fenêtre */
    window.setWindowTitle("BASELFI v1.0");
    /* Taille de la fenêtre */
    window.setFixedSize(800, 600);
    /* Boutons dans la fenêtre */
    layout.addWidget(&obutton);
    layout.addWidget(&cbutton);
    /* Slider dans la fenêtre */
    layout.addWidget(&slider);
    /* Barre dans la fenêtre */
    layout.addWidget(&bar);
    /* La phrase */
    layout.addWidget(&label);
    /* Lier une action à chaque bouton */
    QObject::connect(&obutton, &QPushButton::clicked, [&window, &file] {file = QFileDialog::getOpenFileName(&window, QObject::tr("Sélectionner un fichier audio ..."), "C:/", QObject::tr("Audio (*.mp3)"));});
    QObject::connect(&cbutton, SIGNAL(clicked()), &program, SLOT(quit()));
    /* Lier la barre de progression au slider */
    QObject::connect(&slider, &QSlider::valueChanged, &bar, &QProgressBar::setValue);
    /* Modifier la phrase avec le slider */
    QObject::connect(&slider, &QSlider::valueChanged, &label, &QLabel::setText(QString("I am %1 years old !").arg(int)));
    /* Inscrire les widgets dans la fenêtre */
    window.setLayout(&layout);
    /* Montrer la fenêtre */
    window.show();
    /* Exécution de la fenêtre */
    return program.exec();
}

Sorry, I forgot my code.

raven-worx

@Meugiwara said in Modify a QLabel with a QSlider:

If I don't use class, how can I add your code in the main function ?

This is only possible if you are compiling with a C++11-compatible compiler.

connect(&slider, &QSlider::valueChanged, [label](int value) {
  label.setText( QString("I am %1 years old").arg(value);
});

Meugiwara

Thank you a lot and I have just a little question about the QLabel. At the kick-off of the program, the QLabel doesn't appear, but if I move the QSlider, I can see it. How do you do to see everytime the QLabel ?

mrjj

@Meugiwara
Hi
Try call setText on it just after its created.

Meugiwara

I wrote this :

label.setText(QString("I am 0 years old !"));

This is like an initialization because the counter begins at 0. Thank you !