Question

I want to create a custom widget that contains a QSpinBox. I want the custom widget to expose some of QSpinBox’s properties as its own so it can work conveniently in Designer.

Is there a convenient way to do this kind of property proxying in Qt?

I want to reiterate that the relationship between my custom widget and the QSpinBox is containment, not inheritance. I am using pyqt, but will happily accept a pure qt answer.

To clarify, I want to create variations of standard widgets that have some extra decorations. For example, I will be adding a toggleable icon to sit beside my QSpinBox. However I still want to be able to configure the QSpinBox in designer (ie, set the suffix, upper and lower limits, increment, etc).

Answer 1

Alrite, so here’s a way to do it.

It’s better than writing a function manually for each property. Basically, you write a macro that expands the code for you.
I have a doubleSpinBox in my widget and its value is changed whenever I change the property. And you emit a signal whenever the property changes, which is connected to the doubleSpinBox->setValue(). Tested and works perfectly.
Complete code at this link.

#ifndef MYWIDGET_H_
#define MYWIDGET_H_

#include <QtGui/QWidget>
#include <QtGui/QLabel>
#include "ui_mywidgetform.h"

#define MYPROPERTY_SET_FUNC(_PROPCLASS_, _PROP_PARAM_NAME_, _PROP_SET_FUNC_NAME_, _PROP_NOTIFY_) \
  void _PROP_SET_FUNC_NAME_(_PROPCLASS_ _PROP_PARAM_NAME_) \
  { \
    emit _PROP_NOTIFY_(_PROP_PARAM_NAME_); \
  }

#define MYPROPERTY_GET_FUNC(_PROPCLASS_, _PROP_READ_FUNC_NAME_, _PROP_VARIABLE_)\
  _PROPCLASS_ _PROP_READ_FUNC_NAME_() const  \
  { return _PROP_VARIABLE_; }

class MyWidget : public QWidget
{
  Q_OBJECT

public:
  MyWidget(QWidget *parent = 0);
  ~MyWidget();
  enum Accuracy {Good, Bad};

signals:
  void doubleSpinBoxValueChanged(double);
  void accuracyChanged(Accuracy);

private:
    Q_PROPERTY(Accuracy accuracy READ accuracy WRITE setAccuracy NOTIFY accuracyChanged)
    Q_PROPERTY(double doubleSpinBoxValue READ doubleSpinBoxValue WRITE setDoubleSpinBoxValue)

private:
  Accuracy m_accuracy;  //custom class property
  Ui::Form m_ui;

public:
  //Getter functions
  MYPROPERTY_GET_FUNC (double, doubleSpinBoxValue, m_ui.doubleSpinBox->value())
  MYPROPERTY_GET_FUNC (Accuracy, accuracy, m_accuracy)
  //Setter functions
  MYPROPERTY_SET_FUNC(Accuracy, accuracy, setAccuracy, accuracyChanged)
  MYPROPERTY_SET_FUNC(double, doubleSpinBoxValue, setDoubleSpinBoxValue, doubleSpinBoxValueChanged)

};

#endif // MYWIDGET_H_