Base class and Derived classes (inheritance question)

Hi I would like to know if it is possible to execute a function from a derived class that inherits from a base class and trigger it on all the derived classes.

For example I have a base class with a generic template widget (for user interface), it has several functionality that can be called by the derived classes.

Then I have a class that inherits this user interface.

If for example I call the protected function of the baseclass through the instance of the derived class, is there a way that I can trigger it for all derived classes that inherit the function of the base class?

Quote:

---

Originally Posted by ehnuh

Hi I would like to know if it is possible to execute a function from a derived class that inherits from a base class and trigger it on all the derived classes.

---

With an exception of static methods, you execute functions on objects and not classes, therefore for this to work, each instance has to be registered somewhere. If you keep such a register in the base class then I can imagine this working (I have no idea why you'd want to do that though). Here is an example:

Code:

---

class BaseClass {
public:
  BaseClass() {
    m_instances << this;
  }
  ~BaseClass() {
    m_instances.removeOne(this);
  }
  virtual void someMethod() {
    // ...
    foreach(BaseClass *instance, m_instances) {
      if(instance != this) instance->someOtherMethod(); // or someMethod() but you have to make sure it is overridden correctly in each subclass or you'll get incorrect behaviour
    }
    // ...
  }
  virtual void someOtherMethod() {
 
  }
private:
  static QList<BaseClass*> m_instances; // register of instances
};
 
class SubClass : public BaseClass {
public:
  SubClass() : BaseClass() {}
  virtual void someOtherMethod() { ... }
};

---

I think in Qt there's a possibility of doing this using singal and slots. Emitting a signal when the base class function is called, where the signal -in all instances of the derived class- is connected to a slot which calls the base class function. The signal can carry a variable which informs the slot that it should not emit the signal again to prevent a loop.