How to get type of a derived class from another derived class

Question

I have the (pseudo) code:

public class GlobalClass
{
    public GlobalClass()
    {
        var x = this.GetType().Name // Returns "Channels"
        // WHAT TO DO HERE?
    }
}

public class BaseClass
{
    public string Title { get; set; }
}

And using this code:

public class Channels : GlobalClass
{
    public Channels()
    {

    }

    public class Channel : BaseClass
    {

    }
}

Where the comment is (// WHAT TO DO HERE?), I want to get the runtime type of BaseClass, where in my sample code should return Channel.

I am open to different approaches, but only if it's accompanied with an explanation why I should change the code.

What are you trying to do, actually? Why do you think you need this type? What if `GlobalClass` inherits a different class? Which class type will you need in that case? — vgru, Jan 31 '12 at 09:21
i have 3-5 class which have the same properties and methods, all i want to do is stop repeating my code in each and every class. i know its a little over my head, but i am willing to learn :) — Rafael Herscovici, Jan 31 '12 at 09:45
why the Close request? there is no duplicate for this question and i found no information googling it. please explain. — Rafael Herscovici, Jan 31 '12 at 09:46
*i want to do is stop repeating my code in each and every class*: Yes, inheritance will help you achieve this. But there is rarely a need to access the **type** of the base class when doing this. What do you want to do with this type? — vgru, Jan 31 '12 at 09:53
@Groo the data for those classes are loaded from files, which reside each in the appropiate folder name ( the folder name is the same as the class ). — Rafael Herscovici, Jan 31 '12 at 10:40

score 2 · Answer 1 · answered Jan 31 '12 at 09:27

I think you need a generic class here, something like:

    public class GlobalClass<T> where T : BaseClass
    {
        public GlobalClass()
        {
            var theType = typeof(T);    //you got it
        }
    }
    public class BaseClass
    {
        public string Title { get; set; }
    }

    public class Channel : BaseClass { }
    public class Channels : GlobalClass<Channel> { }

Azodious · Answer 2 · 2012-01-31T09:23:58.770

is operator is just for that purpose.

getType() method with class Type can also be used.

class Example 
{
    static void ShowTypeInfo (object o) 
    {  
        Console.WriteLine ("type name = {0}, 
                            full type name = {1}", o.GetType(), 
                            o.GetType().FullName ); 
    }

    public static void Main()
    { 
        long longType = 99; 
        Example example= new Example(); 

        ShowTypeInfo (example); 
        ShowTypeInfo (longType); 
    }
}

score 0 · Answer 3 · edited May 23 '17 at 10:34

To get the runtime type of anything, you first need an object instance to get the type from. So with your given structure, that's not possible.

There are two possible approaches:

Add a BaseClass parameter to the constructor of your GlobalClass:

public class GlobalClass
{
    public GlobalClass(BaseClass data)
    {
        var dataType = data == null ? null : data.GetType();
        // do something with the type
    }
}

public class Channels : GlobalClass
{
    public Channels(Channel data) : base(data)
    {

    }

    public class Channel : BaseClass
    {

    }
}

Pass the type to the constructor directly:

public class GlobalClass
{
    public GlobalClass(Type actualType)
    {
        Debug.Assert(typeof(BaseClass).IsAssignableFrom(actualType));
    }
}

public class Channels : GlobalClass
{
    public Channels() : base(typeof(Channel))
    {

    }

    public class Channel : BaseClass
    {

    }
}

If the structure for some reason doesn't allow generics here (as Danny Chen suggested), I'd personally prefer the second approach, since that doesn't need an actual instance.

score 0 · Accepted Answer · edited May 23 '17 at 12:10

0

You can use reflection like this:

using System.Reflection;

...

public class GlobalClass
{
    public GlobalClass()
    {
        Type[] types = Assembly.GetExecutingAssembly ().GetTypes ();
        foreach ( Type t in types )
        {
            if ( t.BaseType == typeof ( BaseClass ) )
            {
                Console.WriteLine ( "I found a class " + t.Name + " that subclass BaseClass" );
            }
        }
    }
}

See also Stack Overflow question List of classes in an assembly.

edited May 23 '17 at 12:10

Community

1
1

answered Jan 31 '12 at 09:34

Alexis Pautrot

1,128
1
14
18

this works, but are there any disadvantages i should be aware of? – Rafael Herscovici Jan 31 '12 at 09:43

How to get type of a derived class from another derived class

4 Answers4