C＃继承的类列表

Question

I have the following classes:

public class BaseClass() {}
public class Class1 : BaseClass {}
public class Class2 : BaseClass {}

public class BaseClassList : List<BaseClass> {}
public class Class1List : List<Class1> {}
public class Class2List : List<Class2> {}

The data is in JSON format are is loaded as a list of BaseClass objects. Once loaded and want to populate the specific lists with the relevant objects:

public void Setup()
{
    Class1List list1 = new Class1List();

    var query = from x in BaseClassList
                where x.Type = MyType.Class1
                select x;

    list1.AddRange(query);
}

However AddRange doesn't compile because I'm trying to added BaseClass objects to a Class1 list.

How can I successfully add the inherited classes?

Answer 1

Try this code snippet,

public void Setup()
{
  Class1List list1 = new Class1List();

  var query = from x in BaseClassList
            where x.GetType() == typeof(Class1)
            select x as Class1;

  list1.AddRange(query);
}

The as operator casts your type BaseClass to type Class1

Reference: MSDN as Operator

As mentioned in a comment, you can do it a little bit more save with this snippet:

public void Setup()
{
  Class1List list1 = new Class1List();

  var query = from x in BaseClassList
        where x.GetType() == typeof(Class1)
        select x;

   foreach(var item in query){
      var temp = item as Class1;
      if(temp  != null)
         list1.Add(temp);
   }
}

After casting to Class1 you can check for null, as the as operator returns null if unable to cast. I would prefer to make a type compare with where x.GetType() == typeof(Class1)