Getting variables from inherited class in c#

Question

I have a problem where i have a list of one class (DrawableGameComponent) with many instances of different types of classes inherited from DrawableGameComponent.

The thing is i want to access a variable from one of those classes, but since they are declared as a DrawableGameComponent, i can't access any other variable than DrawableGameComponent has.

main class:

List<DrawableGameComponent> entities = new List<DrawableGameComponent>();

"player" class:

public Color color;
public int score;

any idea of how i can access these variables from the main class?

The base class should not need to access members of a child class. You should probably have the base class call an abstract method and let the child implement whatever logic needs the child class's members. — cadrell0
– cadrell0, Commented Feb 24, 2012 at 15:36

Maciej · Accepted Answer · 2012-02-24 15:38:27Z

2

If DrawableGameComponent is base for Player you can do this:

foreach(DrawableGameComponent entity in entities)
{
    Player player = entity as Player;
    if(player != null)
    {
        Color col = player.color;
        int score = player.score;
    }
}

Beacause 'is', 'as' and casting are relatively expensive it is preferred to do it just once - as above.

answered Feb 24, 2012 at 15:38

Maciej

7,9811 gold badge34 silver badges36 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

TimW · Accepted Answer · 2012-02-24 15:38:19Z

1

Ryan P's got the right of it. If you're sure that Player derives from DrawableGameComponent, you can cast the instance of DrawableGameComponent to Player as shown above.

However, consider that some of those DrawableGameComponent instances may be something other than Player. Perhaps Enemy, for instance. You don't say specifically what you're doing with the instance, but this sort of downcast usually represents a design problem.

Just something to consider.

answered Feb 24, 2012 at 15:38

TimW

731 silver badge6 bronze badges

Comments

Amfasis · Accepted Answer · 2012-02-24 15:41:22Z

1

It seems like your inheritance-model is wrong: if a variable (I assume Color in your example) is declared in all/most derived classes (like player, bot, opponent etc) it should be declared in the base class. Derived classes that dont use the Color can ignore it

answered Feb 24, 2012 at 15:41

Amfasis

4,2362 gold badges20 silver badges33 bronze badges

Comments

kitti · Accepted Answer · 2012-02-24 15:33:46Z

0

Assuming these classes are in the same project (scope), you can use the following:

if (dgc is Player)
{
    (dgc as Player).color = Colors.Red;
}

answered Feb 24, 2012 at 15:33

kitti

14.9k33 silver badges50 bronze badges

3 Comments

kitti Over a year ago

@AskI.Nator Great! Since this answer was helpful, please accept it by clicking the checkmark next to it!

Fredrik Mörk Over a year ago

While this is technically correct, from a system design perspective it's a very bad idea to have a base class that is aware of derived classes and that act on such knowledge. If nothing else, it potentially breaks the "L of SOLID.

Maciej Over a year ago

This is not optimal way of doing it - you cast the same thing twice ('is' also casts behind scenes)

dice · Accepted Answer · 2012-02-24 15:36:21Z

0

the short answer is

if(entity[0] is Player)
{
   ((Player)entity[0]).color
}

answered Feb 24, 2012 at 15:36

dice

2,8801 gold badge23 silver badges34 bronze badges

Comments

Scott M. · Accepted Answer · 2012-02-24 15:40:28Z

0

I'm assuming you know that you can cast something like so:

Player p = (Player)entities[0];

So what I think you have is a design problem. You can always use the is operator to figure out if the entity is a Player but you may end up with problems down the road if you ahve too much RTTI going on. If its just this one instance, casting is a good choice because it's kind of necessary.

answered Feb 24, 2012 at 15:40

Scott M.

7,34732 silver badges39 bronze badges

Comments

kaj · Accepted Answer · 2012-02-24 16:08:26Z

0

If you want to access properties defined in the inherited class then you need to cast it to that type. DrawableGameComponent type instances can only expose properties within it (or any type it inherits from eg system.object)

So if you have the following:

class Player : DrawableGameComponent  
{  
  public int MyWidth { get; set; }  
}

Then you can only access the MyWidth property when you have a Player instance:

Player playerObj = dgcObj as Player;  
if (playerObj != null) Console.Write(playerObj.MyWidth);

Whereas the following won't work:

DrawableGameComponent dgcObj = new Player();  
dgcObj.MyWidth // no such property

edited Feb 24, 2012 at 16:08

answered Feb 24, 2012 at 15:40

kaj

5,2712 gold badges23 silver badges18 bronze badges

Collectives™ on Stack Overflow

Getting variables from inherited class in c#

7 Answers 7

Comments

Comments

Comments

3 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

Comments

Comments

Comments

3 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related