How to change QLabel value after Pushbutton pressed?

[rdelgado]

Hello,

I need to know how to change the value or text displayed in a QLabel after a PushButton is pressed.
I have 2 buttons on my program. One PushButton is to trigger some math calculations. I want to display the result of the calculation after it is completed in a QLabel, but to display it only when I press the other PushButton. Then, if I do the math again, display the new result by pressing the other button and so on.

¿Can I use a PushButton clicked() signal to change a QLabel value?

Thank you very much!!!!

[Lykurg]

Yes, connect the clicked signal to a slot and in that slot you can set the text of your label.

[rdelgado]

Hi,

I did this:

main.cpp

#include <QApplication>
#include <QLabel>
#include <QPushButton>
#include <QVBoxLayout>
#include <QWidget>
#include <QString>
 
 
class MyWidget : public QWidget
{
public:
    MyWidget(QWidget *parent = 0);
 
    QLabel *label;
    QString string;
 
signals:
 
public slots:
    void setTextLabel();
 
};
 
void MyWidget::setTextLabel()
{
    label->setText("Test");
}
 
MyWidget::MyWidget(QWidget *parent) :
    QWidget(parent)
{
    QPushButton *quit = new QPushButton("Quit");
    QPushButton *showtext = new QPushButton("Show");
    label = new QLabel;
 
    QObject::connect(quit, SIGNAL(clicked()), qApp, SLOT(quit()));
    QObject::connect(showtext, SIGNAL(clicked()), this, SLOT(setTextLabel()));
 
    QVBoxLayout *layout = new QVBoxLayout;
 
    layout->addWidget(label);
    layout->addWidget(showtext);
    layout->addWidget(quit);
    setLayout(layout);
}
 
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MyWidget widget;
    widget.show();
    return app.exec();
}

#include <QApplication>
#include <QLabel>
#include <QPushButton>
#include <QVBoxLayout>
#include <QWidget>
#include <QString>


class MyWidget : public QWidget
{
public:
    MyWidget(QWidget *parent = 0);

    QLabel *label;
    QString string;

signals:

public slots:
    void setTextLabel();

};

void MyWidget::setTextLabel()
{
    label->setText("Test");
}

MyWidget::MyWidget(QWidget *parent) :
    QWidget(parent)
{
    QPushButton *quit = new QPushButton("Quit");
    QPushButton *showtext = new QPushButton("Show");
    label = new QLabel;

    QObject::connect(quit, SIGNAL(clicked()), qApp, SLOT(quit()));
    QObject::connect(showtext, SIGNAL(clicked()), this, SLOT(setTextLabel()));

    QVBoxLayout *layout = new QVBoxLayout;

    layout->addWidget(label);
    layout->addWidget(showtext);
    layout->addWidget(quit);
    setLayout(layout);
}


int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MyWidget widget;
    widget.show();
    return app.exec();
}

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But it gives me the following Application Output error:

Starting /home/simulab-3/Documentos/Qt/Training2010/Texto/Texto-build-desktop/Texto...
Object::connect: No such slot QWidget::setTextLabel() in ../Texto/main.cpp:37

So what is wrong?

Thank you very much!!!

[Lykurg]

Use the Q_OBJECT macro and put each class in a separate file or explicit include the moc file.

[rdelgado]

Hi,

Did the Q_OBJECT and the separate files and it worked! Thanks a lot!