How to share property in different classes?

alex2202375

In my project there are many classes some of which have the same property, I want to reuse those property definitions in different classes, but could not find a way.
E.g: There are three properties:name, pic, desc which are used by class A,B,C. I don't want to write the properties multiple times in different class. Is there anyway to do that?
@class A: public QObject
{
Q_OBJECT
Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)
Q_PROPERTY(QString pic READ pic WRITE setPic NOTIFY picChanged)
public:
A(QObject *parent = 0);

QString name();
void setName(QString name);

QString pic();
void setPic(QString pic);

signals:
void nameChanged();
void picChanged();

private:
QString m_name;
QString m_pic;
}

class B: public QObject
{
Q_OBJECT
Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)
Q_PROPERTY(QString desc READ desc WRITE setDesc NOTIFY descChanged)
public:
B(QObject *parent = 0);

QString name();
void setName(QString name);

QString desc();
void setDesc(QString desc);

signals:
void nameChanged();
void descChanged();

private:
QString m_name;
QString m_desc;
}

class C: public QObject
{
Q_OBJECT
Q_PROPERTY(QString pic READ pic WRITE setPic NOTIFY picChanged)
Q_PROPERTY(QString desc READ desc WRITE setDesc NOTIFY descChanged)
public:
C(QObject *parent = 0);

QString pic();
void setPic(QString pic);

QString desc();
void setDesc(QString desc);

signals:
void picChanged();
void descChanged();

private:
QString m_pic;
QString m_desc;
}@

lgeyer

-Sounds like classic example for inheritance.-

I've just realised that your classes use different properties.

You might create a template class which has storage, a setter and a getter for a property (and see if such a case is supported by the Q_PROPERTY implementation).
Or you use a preprocessor macro (or a combination of both) which expands to the actual code.

alex2202375

[quote author="Lukas Geyer" date="1312642365"]Sounds like classic example for inheritance.[/quote]

No, can not use multiple inheritance, because multiple QObject inheritance is not supported, but Q_PROPERTY definition needs class to inherit from QObject.

lgeyer

[quote author="Alex Liu" date="1312642738"]
[quote author="Lukas Geyer" date="1312642365"]Sounds like classic example for inheritance.[/quote]

No, can not use multiple inheritance, because multiple QObject inheritance is not supported, but Q_PROPERTY definition needs class to inherit from QObject.

[/quote]

There is no need to inherit QObject multiple times as the base class already inherits QObject (which allows for using properties).

alex2202375

@Lukas Geyer
Could you give some example code which B,C can share the same code for property desc, A,B for name, A,C for pic? I tried use MICRO, it would not work.

lgeyer

I just tried the template solution and passing member functions as setters and getters to Q_PROPERTY does, as suspected, not work.

The preprocessor solution does work as expected.
@
#define PROPERTY(Type, Name) private:
Type Name;
public:
void set##Name(Type value) { Name = value; }
Type get##Name() const { return Name; }

// ...

class A : public QObject
{
Q_OBJECT

Q_PROPERTY(QString name READ getname WRITE setname)
Q_PROPERTY(QString description READ getdescription WRITE setdescription)

PROPERTY(QString, name)
PROPERTY(QString, description)

};
@
You cannot include the Q_PROPERTY macro in the PROPERTY macro as the source files are moc'ed before preprocessed and moc does not replace in macros.

alex2202375

Thanks Lukas, I even don't want to write Q_PROPERTY definition. But as you mentioned, because of the moc, MACRO for define Q_PROPERTY does not work, and in other hand, multiple inheritance is not work too. So I think I need to write properties for each class separately.

giesbert

Hi,

MOC can't work with #defines, we also wanted to do such things :-(
BUt it just scans the source code and has no pre processor working in front.

So you will have to type it in each class seperately...

alex2202375

Thanks guys, looks I still need to manually write the code many times:(

joonhwan

Though it has been quite old post, I think it's interesting topic. Hmm. How about introducing another simple moc-like code generating tool for this, if there is a certain reason why moc cannot not support getter/setter generation like this.