QSlider does not reach max or min

[Fabian727]

Hi guys,

I create a new window by hand, because I use the QColorWheel, which is not compatible with the QT Creator Designer. ( I use QT 5.10)
The window is created and I can use it. Only problem is, if I move the slider by hand, I can't reach the set maximum and minimum values (0 and 255). The changes are made visible in the QLine underneath. I also can change the value of the slider by this line. There it is possible to set the min/ max values, which are then accepted and realized on the slider.

What do I need to reach the end of the slider/ min/max values by moving my mouse.

thanks in advance,
Fabian

p.s.: here is the code for creating the slider

    /*reset the color to black*/
    activeColor.setAlpha(0);
    activeColor.setRed(0);
    activeColor.setGreen(0);
    activeColor.setBlue(0);

    /*set up the main window */
    QScreen *ratio = QGuiApplication::primaryScreen();
    window->setGeometry(ratio->geometry().width()-250,0,250,250);
    window->setFixedSize(250,250);
    window->setObjectName("ColorPicker");

    /* Graphical Objects */
    QWidget     *windowCentral    = new QWidget(window);
    QGridLayout *windowLayout     = new QGridLayout(windowCentral);
    windowColorWheel = new ColorWheel(window);

    windowWhiteSlider = new QSlider(window);
    windowWhiteSlider->setRange(0,255);
    windowWhiteSlider->setOrientation(Qt::Horizontal);
    windowWhiteSlider->setTickInterval(1);
    windowWhiteSlider->setSingleStep(1);
    windowWhiteSlider->setPageStep(10);

    windowLine = new QLineEdit(window);
    windowLine->setMaximumWidth(100);

    windowLayout->setObjectName("centralLayout");
    windowLayout->addWidget(windowColorWheel);
    windowLayout->addWidget(windowWhiteSlider);
    windowLayout->addWidget(windowLine);

    windowCentral->setLayout(windowLayout);

    window->setCentralWidget(windowCentral);

    /* Actions */
    windowActionQuit = new QAction(window);
    windowActionQuit->setShortcut(QKeySequence("Ctrl+Q"));

    windowActionClose = new QAction(window);
    windowActionClose->setShortcut(QKeySequence("Ctrl+W"));

    window->addAction(windowActionQuit);
    window->addAction(windowActionClose);

    /* window connections */
    connect(windowActionClose,SIGNAL(triggered()),window,SLOT(close()),Qt::DirectConnection);                    //close by Ctrl+W

    //colorwheel or slider changed, update the textline
    connect(windowColorWheel,SIGNAL(colorChanged(QColor)),window,SLOT(setLine(void)),Qt::DirectConnection);      //if color wheel is changed, change text line
    connect(windowWhiteSlider,SIGNAL(sliderMoved(int)),window,SLOT(setLine(void)),Qt::DirectConnection);

    //the textline was changed, update colorwheel and slider
    connect(windowLine,SIGNAL(editingFinished()),window,SLOT(setColor()),Qt::DirectConnection);
    connect(windowLine,SIGNAL(returnPressed()),window,SLOT(setColor()),Qt::DirectConnection);

[joeQ]

@Fabian727 Hi, friend. Welcome.

can you qDebug QSlider value in slot function of setLine, and why did you use void not int in slot function?

connect(windowWhiteSlider,SIGNAL(sliderMoved(int)),window,SLOT(setLine(void)),Qt::DirectConnection);

void -> int, and qDebug value in slot function.

connect(windowWhiteSlider,SIGNAL(sliderMoved(int)),window,SLOT(setLine(int)),Qt::DirectConnection);

[ambershark]

I'm unable to duplicate your issue. I put this code together to test based on your creation of windowWhiteSlider and everything works fine. I can get to 0 and to 255 with the mouse.

#include <QApplication>
#include <QSlider>
#include <QHBoxLayout>
#include <QLabel>
#include <QDebug>

int main(int ac, char **av)
{
        QApplication app(ac, av);

        auto window = new QWidget();
        window->resize(300,150);

    auto windowWhiteSlider = new QSlider(window);
    windowWhiteSlider->setRange(0,255);
    windowWhiteSlider->setOrientation(Qt::Horizontal);
    windowWhiteSlider->setTickInterval(1);
    windowWhiteSlider->setSingleStep(1);
    windowWhiteSlider->setPageStep(10);
        windowWhiteSlider->setValue(0);

        auto label = new QLabel(window);
        label->setText(QString::number(windowWhiteSlider->value()));
        QObject::connect(windowWhiteSlider, &QSlider::valueChanged, 
                        label, [=](int v) { label->setText(QString::number(v)); });

        auto layout = new QHBoxLayout();
        layout->addWidget(windowWhiteSlider);
        layout->addWidget(label);
        window->setLayout(layout);

        window->show();

        return app.exec();
}

Can you give us a video or a screenshot or more information on what the problem is? I was unable to duplicate it with what you shared.

[Magge2k]

Hello,

today i wanted to introduce a Slider which works from INT32_MAX to INT32_MIN.
But this is not possible.

Initial State with Limits => INT32_MAX, INT32_MIN

When Clicking and Sliding

After Release

I found out that the Limit for a good Version Working is at INT32_MAX/2, INT32_MIN/2
Initial

Lower Limit

Upper Limit

So my Question, is this a Bug or a Feature?

I used Qt 5.15.2 with c++14.

Thanks and Bye

[Christian Ehrlicher]

Since sliderPosition is only a signed int, the max range can also be max 2^31-1.
A slider with such a huge range is useless since a user can never do a valid input then. Scale your slider values.

[Magge2k]

Ah OK, so internal Range is also signed int32 and not unsigned int32.

The Scale Idea is a good workaround and you are right.
But for quick random value setting i thought it would be easy just to use the value and define the maximum Limits.

[Christian Ehrlicher]

@Magge2k said in QSlider does not reach max or min:

Ah OK, so internal Range is also signed int32 and not unsigned int32.

Yes: https://doc.qt.io/qt-5/qabstractslider.html#value-prop