Subclass QDial

Punt

Hi, I would like to subclass QDial because :

Here the QDial can jump values (ex : what I want : If QDial.value() = 2, I want the QDial able to move only to 1 or 3.

So I tried :

#ifndef CUSTOMDIAL_H
#define CUSTOMDIAL_H

#include <QObject>
#include <QDial>
#include <QMouseEvent>

class CustomDial : public QDial
{
    Q_OBJECT
public:
    CustomDial(QWidget * parent = nullptr);

private:
virtual void mousePressEvent(QMouseEvent *e) override;
};
#endif // CUSTOMDIAL_H

I started to try only by overriding mousePressEvent() and if this work I'll also do it for other mouse-related function.

In order to do that, I took mousePressEvent from Qt source:

void QDial::mousePressEvent(QMouseEvent *e)
{
    Q_D(QDial);
    if (d->maximum == d->minimum ||
        (e->button() != Qt::LeftButton)  ||
        (e->buttons() ^ e->button())) {
        e->ignore();
        return;
    }
    e->accept();
    setSliderPosition(d->valueFromPoint(e->pos()));
    // ### This isn't quite right,
    // we should be doing a hit test and only setting this if it's
    // the actual dial thingie (similar to what QSlider does), but we have no
    // subControls for QDial.
    setSliderDown(true);
}

and tried to make some adjustment :

void CustomDial::mousePressEvent(QMouseEvent* e)
{
    int oldValue = value();

    //copy the beggining of Qt source :
Q_D(QDial);
    if (d->maximum == d->minimum ||
        (e->button() != Qt::LeftButton)  ||
        (e->buttons() ^ e->button())) {
        e->ignore();
        return;
    }
    e->accept();
    //And now change the setValue if there is a difference like this :
   int newValueFromMouse =  d->valueFromPoint(e->pos());
   int diff = newValueFromMouse - oldValue;

   if(diff > 1)
      setSliderPosition(oldValue +1);
   else if(diff < -1)
      setSliderPosition(oldValue -1);
   else
      setSliderPosition( newValueFromMouse);


}

In my opinion, the algorith should works right?

But there is a problem with the variable 'd' :

C:\Qt\5.6\mingw49_32\include\QtCore\qglobal.h:1018: erreur : 'QDialPrivate* QDial::d_func()' is private
     inline Class##Private* d_func() { return reinterpret_cast<Class##Private *>(qGetPtrHelper(d_ptr)); } \

And I don't understand why ?! I mean I understand the problem, but I don't understand why there is this mistake if I just used Qt source code...

mrjj

hi
you are trying to call private stuff.
http://zchydem.enume.net/2010/01/19/qt-howto-private-classes-and-d-pointers/

https://forum.qt.io/topic/516/why-the-excessive-use-of-private-classes/2

Punt

@mrjj

Hi, thanks for your answer but..
How do I procede ?

mrjj

@Punt said:

QDial

well i never tried to use privates as they are private for a reason
but i think you need to include
private\xxx_p.h file but I dont see any for QDial.

Sorry. Im not sure how to allow this.

michelson

How about:

In slot connected to sliderPressed save old value
Set tracking http://doc.qt.io/qt-4.8/qabstractslider.html#tracking-prop
In slot connected to valueChanged signal have something like:

//valueChanged(int value)
if( value > (old_value+1)  )
   dial->setValue(old_value + 1);
else if( value < (old_value-1) )
  dial->setValue(old_value - 1);

Two regards:

not sure if i understood what you want to achive corectly
above code is not tested, just a sketch