CODEWITHSUNDEEP
c#listvariablespolymorphismparent-child
Joel Babineau
Joel Babineau

Reputation: 3

List of <BaseClass> and accessing childs variables

I'm creating a dialogue system and I wanna use polymorphism to make the job easier so I have a class thats the dialogue tree which holds List dialogue_tree... and then I have TextBoxNPC,TextBoxText,TextBoxItem etc so I can have each page display a different type of dialogue box if I so desire. each TextBox holds an enum of what type of textbox it is and the problem arrises when I want to change variables that arn't in the base class.

public class Dialogue_Tree
{

    List<TextBox> dialogues = new List<TextBox>();

    public Dialogue_Tree()
    {
        dialogues.Add(new TextBoxNPC());
        dialogues[0].
    }
}

if in textboxnpc I have Sprite npc_portrait I can't change it cause its being treated as TextBox. so even if I cast it, I get a null exception is there anyway to do this?

my only other option would be having only a single class TextBox and it having every variable needed for every different type of dialogue but then theres like 35 unused variables per textbox page which seems like a waste of resources.

Upvotes: 0

Views: 31

Answers (1)

Caius Jard
Caius Jard

Reputation: 74710

You've got your understanding of polymorphism upside down. If you had a drawing program that used this polymorphic:

abstract class Shape {
  public int X = 0;
  public int Y = 0;
}

class Rectangle:Shape {
  public int Width = 10;
  public int Height = 20;
}

class Circle:Shape {
  public int Diameter = 50;
}

You wouldn't, in the parent class, look at the type of the child and do something different:

foreach(Shape s in _listOfShapes){
  if(s is Circle c)
    myCanvas.DrawCircle(c.X,c.Y,c.Diameter);
  else if(s is Rectangle r)
    myCanvas.DrawRectangle(c.X,c.Y,r.Width,r.Height);
}

You create a way to treat all the shapes the same:

abstract class Shape {
  public int X = 0;
  public int Y = 0;
  abstract void DrawYourself(Canvas c)
}

class Rectangle:Shape {
  public int Width = 10;
  public int Height = 20;
  override DrawYourself(Canvas c){
    c.DrawRectangle(base.X,base.Y,this.Width,this.Height);
  }
}

class Circle:Shape {
  public int Diameter = 50;
  override DrawYourself(Canvas c){
    c.DrawCircle(base.X,base.Y,this.Diameter);
  }
}

Now all shapes know how to draw themselves on a canvas (that the parent owns) you treat them all as plain old shapes:

foreach(Shape s in _listOfShapes){
  s.DrawYourself(myCanvas);
}

Upvotes: 1

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