about properties

[jajdoo]

this might be a silly question, but still..
taking the following example from the qt docs:

class MyClass : public QObject
 {
     Q_OBJECT
     Q_PROPERTY(Priority priority READ priority WRITE setPriority NOTIFY priorityChanged)
     Q_ENUMS(Priority)
 
 public:
     MyClass(QObject *parent = 0);
     ~MyClass();
 
     enum Priority { High, Low, VeryHigh, VeryLow };
 
     void setPriority(Priority priority)
     {
         m_priority = priority;
         emit priorityChanged(priority);
     }
     Priority priority() const
     { return m_priority; }
 
 signals:
     void priorityChanged(Priority);
 
 private:
     Priority m_priority;
 };

class MyClass : public QObject
 {
     Q_OBJECT
     Q_PROPERTY(Priority priority READ priority WRITE setPriority NOTIFY priorityChanged)
     Q_ENUMS(Priority)

 public:
     MyClass(QObject *parent = 0);
     ~MyClass();

     enum Priority { High, Low, VeryHigh, VeryLow };

     void setPriority(Priority priority)
     {
         m_priority = priority;
         emit priorityChanged(priority);
     }
     Priority priority() const
     { return m_priority; }

 signals:
     void priorityChanged(Priority);

 private:
     Priority m_priority;
 };

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I'm having some trouble understanding this: if the property is not dynamic, declared as a class member and i am responsible for emitting its signals and writing the methods it uses, who am i declaring Q_PROPERTY for? what are the advantages of predefined properties over dynamic ones?

[mcosta]

Without Q_PROPERTY you cannot use property related functions (in example QStateMachine, Animations, ...)

Static properties are declared in the class interface so they are explicit for the class users.

[jajdoo]

i'm still kind of lost about this one.. a bit of a hypothetical question, but:
say i have a class that holds a 3d object's properties (location, rotation, etc..) - when would or wouldn't you declare them static properties?

[high_flyer]

I think you don't understand what Q_PROPERTY does.
Read here:
http://doc.qt.nokia.com/latest/qobject.html#Q_PROPERTY

[jajdoo]

i do understand what it does, but not completely understand its purpose..

my question became rather vague.. ill re-ask it:
if a property is dynamic, it does makes sense in my head.
if a property is not dynamic, and i need to write its READ, WRITE, NOTIFY etc.. myself, why would i declare it Q_PROPERTY? its already visible and accessible to clients - who or what require the Q_PROPERTY declaration? if i am using the class in pre-compile, i already see how to approach this class member.

i'm probably missing something fundamental here..

[high_flyer]

Properties behave like class data members, but they have additional features accessible through the Meta-Object System.

For example, this way you export properties to Qt designer, to name one use.
read more here:
http://doc.qt.nokia.com/latest/prope...roperty-system