custom GUI objects

in a C++ program I have graphs to which I'd like to add some objects. Those can be, for example, common "stand-alone" objects like text, lines etc, or more "smart" objects of different types which act differently and can be connected to an external model to read/write its state.

The simplest thing I have in mind is creating a common interface to all objects with virtual functions like Draw() etc, but the objects can be essentially different (just like text box and scroll bar are different and thus have a different interface). On the other hand, If I don't create a common interface, I'll need to dispatch on objects types, which is usually consid开发者_StackOverflow社区ered bad practice in C++.

All this is supposed to be kept simple, for example creating widgets and custom message queues would be an overkill, but I want to make something easy to support/extend.

I know there are many patterns for GUI, such as MVC, MVP etc, but those are very general and I'm a bit lost, so if you could give me some directions (or even better, a reference to inspire from) that would be helpful! Thanks.

One possibility would be to use multiple inheritance. Define a drawable base class that only defines enough to draw a visible object, and require all your drawable objects to derive from that. They might (often will) derive from other base classes as well, to define other interfaces they support; that one will just ensure that every item can be drawn when needed.

For flexibility and scalability, you can use interfaces instead of a single base class. For example extend all objects that can be painted from a IDraw interface. If objects can be updated add and implement a IControl interface and so on. This may look first as an overhead but offers you a good scalability.

Edit:

void* Class::GetInterface(const int id)
{
    if (IDraw::GetId() == id)
    {
        return (IDraw*)this;
    }
    else if (IControl::GetId() == id)
    {
        return (IControl*)this;
    }

    return NULL;
}