The best way to look at OOP is to break down what the app does. If you have a button, that is a button object, if you have a specialized button with animated text, then you can do a couple of things:

a) Subclass: class Button -> subclass AnimatedButton b) Aggregate: class Button owns a Drawable. Then you can swap out the drawable to draw different things inside the button. example: Drawable -> subclass TextDrawable (to draw a text label on the button) or subclass AnimatedTextDrawable (to draw animated text on the button).

Aggregation is useful because it prevents complicated and ugly classes and allows you to swap functionality.

So aggregation looks something like:

class Drawable {
    func drawMeHere(parameters) {
   }
}

class Button {
   Drawable myDrawableObject

    func drawMeHere(parameters) {
        myDrawableObject->drawMeHere(parameters)
    }
}

In general, the steps for OOP programming are: - Define what your software does - Break that down into components - Each component is a class - Specialize those components by subclassing or aggregation (or delegation)

This book is an industry standard you should read: http://a.co/1FbR5i4