Question

I have a class Field of which there are two sub-classes AccountField and DecimalField.

ie

class Field{//some properties} 

class DecimalField : Field {...}

class AccountField : Field {...}

I then have another class Data which has a member property of type Field.

But it has problems. If I assign a DecimalField variable to the Field property within Data then I cannot use some properties of DecimalFields and also same for Accountfield variables…

What must I do? Which pattern I must use?

I am using C# 4.0 and MS Studio 2010

Answer 1

Yes you can.

Let’s say that you have your field class like this

public class Field
{
   public string Property1{get;set;}
   public int Property2 {get;set;}
}

and the decimal field class like this

  public class DecimalField:Field
   {
    public int DecimalFieldProperty {get;set;}
}

,and the Accountfield like this

public class AccountField:Field
    {
       public double Balance{get;set;}
}

, and suppose you have a method called DoSomething, which expects a parameter of Field type like the one below

void DoSomething(Field field)
{}

Then to get the concrete type passed in, you can do something like

    void DoSomething(Field field)
    {
        var decimalField = field as DecimalField;

        //Do something with the decimal field instance
        if(decimalField  !=null)
         {
           Console.WriteLine("Decimal Field Property {0}",decimalField .DecimalFieldProperty );
          return;

        }

        //Cast the field as a account field instance
      var accountField = field as AccountField;
       if(accountField !=null)
       {
         Console.WriteLine("Balance {0}", accountField.Balance );

        return;
      }

      //Do something else with the normal field
    Console.WriteLine("Normal Field");

    }