C# abstract class and covariant

Question

i have some code like this:

class DataFilter
{
    List<Animal> animals=null;
    public function1(string TypeOfData)
    {
        if(TypeOfData=="cat"){//get cats from database and do something}
        else if(TypeOfData=="dog")
        {//get dogs & do something}
    }
}
class Animal
{}
class Cat:Animal
{}
class Dog:Animal
{}

if i reuse the DataFilter class:

 class CatFilter:DataFilter
 {
 }

how to reuse list animals property???

how to refactor it to split the function1 into different class

L.B · Answer 1 · 2012-10-18T08:05:23.577

2

 List<Animal> animals = new List<Animal>() { new Dog(), new Cat() };
 foreach (var animal in animals)
      animal.DoSomething();

--

class Animal
{ public virtual void DoSomething() { } }

class Cat : Animal
{ public override void DoSomething() { Console.WriteLine("CAT"); } }

class Dog : Animal
{ public override void DoSomething() { Console.WriteLine("DOG"); } }

--EDIT--

I still can not understand what you really want. But seeing the keyword filter makes me think

var groupedAnimals = animals.GroupBy(a => a.GetType())
                         .Select(g => new { Type = g.Key, Animals = g.ToList() })
                         .ToList();

or

var cats = animals.OfType<Cat>().ToList();

edited Oct 18 '12 at 08:05

answered Oct 18 '12 at 06:09

L.B

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sorry, but that's not what i mean – Scott 混合理论 Oct 18 '12 at 06:18
@Kevin But what you try to mean isn't clear. Would you think to rephrase your question? – L.B Oct 18 '12 at 07:12

cuongle · Answer 2 · 2012-10-18T06:15:51.513

1

You can use concept polymorphism into your design, example:

class DataFilter
{
    List<Animal> animals = new List<Animal>() { new Dog(), new Cat() };

    public function1()
    {
        foreach (var animal in animals)
            animal.Do();
    }
}

abstract class Animal
{
    public abstract void Do();
}

class Cat: Animal
{
    public override void Do() {}  
}

class Dog: Animal
{
    public override void Do() {}
}

edited Oct 18 '12 at 06:15

answered Oct 18 '12 at 06:08

cuongle

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@Kevin: What do you mean? Could you update your question, seems it is not clear much – cuongle Oct 18 '12 at 06:19
i think DataFilter can be a base class – Scott 混合理论 Oct 18 '12 at 06:22
@Kevin: could you update your question for more clear, I still dont get your point – cuongle Oct 18 '12 at 06:24

C# abstract class and covariant

2 Answers2