Get emitted signal from custom method. connect qSlider with qDoubleSpinBox

Question

I would like to connect a QDoubleSpinBox with a horizontal QSlider. I have found enough examples to know that they require different argument types ( double vs. int).

I have found I can connect them using the new QT5 syntax:

QObject::connect(ui->gammaSpinBox, static_cast<void (QDoubleSpinBox::*)(double)>(&QDoubleSpinBox::valueChanged),ui->gammaHSlider, &QSlider::setValue);
QObject::connect(ui->gammaHSlider, &QSlider::sliderMoved,ui->gammaSpinBox, static_cast<void (QDoubleSpinBox::*)(double)>(&QDoubleSpinBox::setValue));

I know that to make this smooth, I need to convert their respective arguments into the others through a separate SLOT/Method. So make the QSlider int values into doubles for example:

//connect gamma hSlider to function that will change value to double
QObject::connect(ui->gammaHSlider, SIGNAL(valueChanged(int)), this, SLOT(notifyValueChanged(int)));

void MainWindow::notifyValueChanged(int value){
       double doubleValue = value / 10.0;
       emit doubleValueChanged(doubleValue);
       ui->statusbar->showMessage(QString::number(doubleValue));
   }

My Question...How do I get the QDoubleSpinBox to take this new converted value? I cant seem to understand how to get the value from the emitted signal doubleValueChanged(doubleValue).

Is there a correct way to do something like this?

QObject::connect(myQSlider, SIGNAL(doubleValueChanged(double)), myQDoubleSpinBox, SLOT(setValue(double)))

When I put all this together, it seems that QDoubleSpinBox will connect and sync up to the QSlider movement. But it will only display its defined value range from the UI editor.

I need my double spin box and slider to increment from 0.8 to 4, in 0.1 increments.

---

Solution:

---in Ui editor set the range and step of the QDoubleSpinbox and QSlider as follows:

slider:

min: 8
max: 50
step: 1
value: 10

qDoubleSpinBox:

min: 0.8
max: 5.0
step: 0.1
value: 1.0

---connect the two widgets signals to methods that update values:

QObject::connect(ui->gammaHSlider, SIGNAL(valueChanged(int)),this,SLOT(sliderValueChanged(int)));

QObject::connect(ui->gammaSpinBox, SIGNAL(valueChanged(double)),this,SLOT(spinValueChanged(double)));

---functions that update the slider and qdoublespinbox values to match scale.

void MainWindow::sliderValueChanged(int value){
    double mIN = 0.8;
    double mAX = 5.0;
    double sTEP = 0.1;
    ui->gammaHSlider->setMaximum(int (mAX/sTEP));
    ui->gammaSpinBox->setDecimals(1);
    ui->gammaSpinBox->setMinimum(mIN);
    ui->gammaSpinBox->setMaximum(mAX);
        double dVal =  value*sTEP;
        ui->gammaSpinBox->setValue(dVal);
    ui->statusbar->showMessage(QString::number(value));
}

void MainWindow::spinValueChanged(double value){
        int sVal =  value*10;
        ui->gammaHSlider->setValue(sVal);
    ui->statusbar->showMessage(QString::number(value));
   }

Answer 1

If you want to control the values displayed in the QDoubleSpinBox from the QSlider with values from a to b with steps of s, you must place the number of steps in the QSlider, also configure the number of figures shown in the QDoubleSpinBox, in addition to its minimum and maximum .

double m = 0.8;
double M = 4.0;
double s = 0.1;
myQSlider->setMaximum(int ((M-m)/s));
myQDoubleSpinBox->setDecimals(1);
myQDoubleSpinBox->setMinimum(m);
myQDoubleSpinBox->setMaximum(M);
connect(myQSlider, &QSlider::valueChanged, [=](int value){
    double val =  m + value*s;
    myQDoubleSpinBox->setValue(val);
});