CODEWITHSUNDEEP
c#generics
user1306322
user1306322

Reputation: 8721

How to find out the type of list items and then create a list of that type of items?

I'm trying to use a generic List<T> custom class MyList<T> for automated items parsing and I'm stuck at creating a return type of MyList<T>. Specifically I don't know how to create such a list with the given type. One thing I can do is find out the type and store it in a Type itemType variable.

This question helped me find out the type of list items.

The catch is I don't know the list type until runtime, so it can't be written explicitly in code.

How do I create a list of items of a certain type using a Type itemType variable?

Upvotes: 1

Views: 92

Answers (2)

Mitchell Lee
Mitchell Lee

Reputation: 456

You can do this using Reflection, for example:

var listType = typeof(List<>);
listType.MakeGenericType(typeof(MyType))

return Activator.CreateInstance(listType);

Another example, if all you have is an instance of "MyType" but don't know what it is until runtime:

public IEnumerable GetGenericListFor(object myObject){
    var listType = typeof(List<>);
    listType.MakeGenericType(myObject.GetType())
    return Activator.CreateInstance(listType);
}

Upvotes: 2

Zolt&#225;n Tam&#225;si
Zolt&#225;n Tam&#225;si

Reputation: 12754

Here is the corresponding MSDN article about dynamically creating generic types given the generic type, and the parameter types. Scroll to "Constructing an Instance of a Generic Type" section around the middle.

Quick sample:

Type d1 = typeof(Dictionary<,>);
Type[] typeArgs = {typeof(string), typeof(int)};
Type constructed = d1.MakeGenericType(typeArgs);
object o = Activator.CreateInstance(constructed);

Upvotes: 0

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