Question

I have drawing program that the user can draw either an ellipse or a line, which both derive from shape. I am creating one rubber band, and depending on what the user is drawing i say

rubberBand = new Ellipse();
//or
rubberBand = new Line();

but if i set the rubber band to line, I cannot access the x1 x2 etc, it says shape does not contain a definition of X1. I tried creating an Ellipse and the casting it to a line but still same issue. How do I resolve this?

Answer 1

This sounds like a basic polymorphism question to me. Think about what are you actually trying to do- for instance, a line has 2 points (X1/Y1, and X2/Y2). An ellipse (an oblong circle) has no such property- it has a width, maybe, and a height, and possibly an X and Y coordinates (or a position property).

I am guessing that you are attempting to adjust the bounds and/or location of the shape when the user is dragging it with the mouse. In this case, the operations that you need to define for the shape depend on what kind of shape it is. For a line, you need to write a method that adjusts X2 and Y2 (or whatever). For an ellipse, you will probably need another method that adjusts shapes that have width, height, left, and top properties. Then you just need to determine which one to call depending on which kind of shape you are dealing with.