Slider Value always return 0

[Javenne]

hi,

I'm trying to make a simple program that gets integers from sliders,
and compute them.

A sample of my code :

data.h

#include <QtGUI>
#include <QObject>
 
#ifndef DATA_H
#define DATA_H
class Data : public QWidget
{
    Q_OBJECT
 
public:
    Data(QWidget *parent = 0);
 
public slots:
    void doSum();
 
private:
    int Z0RealSliderValue;
    int ZLRealSliderValue;
 
    QLineEdit *Product;
 
};
 
#endif // DATA_H

#include <QtGUI>
#include <QObject>

#ifndef DATA_H
#define DATA_H
class Data : public QWidget
{
    Q_OBJECT

public:
    Data(QWidget *parent = 0);

public slots:
    void doSum();

private:
    int Z0RealSliderValue;
    int ZLRealSliderValue;

    QLineEdit *Product;

};

#endif // DATA_H

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data.cpp

#include <QtGUI>
#include "data.h"
 
Data::Data(QWidget *parent)
{
 
    QSlider *Z0RealInput = new QSlider(Qt::Horizontal, this);
    Z0RealInput->setRange(0, 150);
 
    QSlider *ZLRealInput = new QSlider(Qt::Horizontal, this);
    ZLRealInput->setRange(0, 150);
 
    Z0RealSliderValue = Z0RealInput->value();
    ZLRealSliderValue = ZLRealInput->value();
 
    Product = new QLineEdit("Sum");
    Product->setReadOnly(true);
 
    QPushButton *Plot = new QPushButton(tr("Plot"),this);
    connect(Plot, SIGNAL(clicked()), this, SLOT(doSum()));
 
     //layout etc etc
     ....
 
}
 
void Data::doSum()
{
    int Sum = 0;
 
    Sum = ZLRealSliderValue + Z0RealSliderValue;
 
    Product->setText(QString::number(Sum));
 
}

#include <QtGUI>
#include "data.h"

Data::Data(QWidget *parent)
{

    QSlider *Z0RealInput = new QSlider(Qt::Horizontal, this);
    Z0RealInput->setRange(0, 150);

    QSlider *ZLRealInput = new QSlider(Qt::Horizontal, this);
    ZLRealInput->setRange(0, 150);

    Z0RealSliderValue = Z0RealInput->value();
    ZLRealSliderValue = ZLRealInput->value();

    Product = new QLineEdit("Sum");
    Product->setReadOnly(true);

    QPushButton *Plot = new QPushButton(tr("Plot"),this);
    connect(Plot, SIGNAL(clicked()), this, SLOT(doSum()));

     //layout etc etc
     ....

}

void Data::doSum()
{
    int Sum = 0;
    
    Sum = ZLRealSliderValue + Z0RealSliderValue;
    
    Product->setText(QString::number(Sum));

}

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It kept returning 0.

I have tried to change setting the lineedit text with a constant string, and it worked,
so I assume there is nothing wrong with the connection.

Is it how I retrieve the value which make the code not working?

Thanks in advance.

[NullPointer]

Hi,

The problem is that you are getting the values before the user can interact with the controls.
You can remove the variables ZLRealSliderValue and Z0RealSliderValue (which you are initializing with the values from just created sliders) and put the QSlider::value() from each in the function doSum instead of the variables...

HTH.

[Javenne]

Thanks!!

It worked perfectly
Didn't realize that my previous code will ignore the interactions to the sliders.

[ChrisW67]

Your previous code was not ignoring interactions with the sliders. The way it was written there could not possible have been interaction with the sliders between when you created the widget and when you read the value. After that, you never attempted to read the values again.

[Javenne]

Yes, I have changed my code to

data.h

#include <QtGUI>
#include <QObject>
 
#ifndef DATA_H
#define DATA_H
class Data : public QWidget
{
    Q_OBJECT
 
public:
    Data(QWidget *parent = 0);
 
public slots:
    void doSum();
 
private:
 
    QSlider *Z0RealInput;
    QSlider *ZLRealInput;
 
    int Z0RealSliderValue;
    int ZLRealSliderValue;
 
    QLineEdit *Product;
 
};
 
#endif // DATA_H

#include <QtGUI>
#include <QObject>

#ifndef DATA_H
#define DATA_H
class Data : public QWidget
{
    Q_OBJECT

public:
    Data(QWidget *parent = 0);

public slots:
    void doSum();

private:

    QSlider *Z0RealInput;
    QSlider *ZLRealInput;

    int Z0RealSliderValue;
    int ZLRealSliderValue;

    QLineEdit *Product;

};

#endif // DATA_H

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data.cpp

#include <QtGUI>
#include "data.h"
 
Data::Data(QWidget *parent)
{
 
    Z0RealInput = new QSlider(Qt::Horizontal, this);
    Z0RealInput->setRange(0, 150);
 
    ZLRealInput = new QSlider(Qt::Horizontal, this);
    ZLRealInput->setRange(0, 150);
 
    Product = new QLineEdit("Sum");
    Product->setReadOnly(true);
 
    QPushButton *Plot = new QPushButton(tr("Plot"),this);
    connect(Plot, SIGNAL(clicked()), this, SLOT(doSum()));
 
     //layout etc etc
     ....
 
}
 
void Data::doSum()
{
    int Sum = 0;
 
    ZLRealSliderValue = ZLRealInput->value();
    Z0RealSliderValue = Z0RealInput->value();
 
    Sum = ZLRealSliderValue + Z0RealSliderValue;
 
    Product->setText(QString::number(Sum));
 
}

#include <QtGUI>
#include "data.h"

Data::Data(QWidget *parent)
{

    Z0RealInput = new QSlider(Qt::Horizontal, this);
    Z0RealInput->setRange(0, 150);

    ZLRealInput = new QSlider(Qt::Horizontal, this);
    ZLRealInput->setRange(0, 150);

    Product = new QLineEdit("Sum");
    Product->setReadOnly(true);

    QPushButton *Plot = new QPushButton(tr("Plot"),this);
    connect(Plot, SIGNAL(clicked()), this, SLOT(doSum()));

     //layout etc etc
     ....

}

void Data::doSum()
{
    int Sum = 0;

    ZLRealSliderValue = ZLRealInput->value();
    Z0RealSliderValue = Z0RealInput->value();
    
    Sum = ZLRealSliderValue + Z0RealSliderValue;
    
    Product->setText(QString::number(Sum));

}

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And it's working now
Thanks