Create list of variable type

Question

I am trying to create a list of a certain type.

I want to use the List notation but all I know is a "System.Type"

The type a have is variable. How can I create a list of a variable type?

I want something similar to this code.

public IList createListOfMyType(Type myType)
{
     return new List<myType>();
}

Make sure there is no faulty design, as this reeks as one.

Dykam
– Dykam

2010-03-22 15:32:10 +00:00
Commented Mar 22, 2010 at 15:32 — Dykam
– Dykam, Commented Mar 22, 2010 at 15:32

smencer · Accepted Answer · 2010-03-22 15:13:49Z

69

Something like this should work.

public IList createList(Type myType)
{
    Type genericListType = typeof(List<>).MakeGenericType(myType);
    return (IList)Activator.CreateInstance(genericListType);
}

answered Mar 22, 2010 at 15:13

smencer

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2 Comments

kayleeFrye_onDeck Over a year ago

I had to fiddle around with this for a bit before I got it working. I'm a total newbie to using Type, so here is a code snippet other people may find helpful where you call this createList method from your Main or some other method: string[] words = {"stuff", "things", "wordz", "misc"}; var shtuff = createList(words.GetType());

182764125216 Over a year ago

I realize this is old, but @Jan, it this one solved your problem it should be marked as answer. @kayleeFrye_onDeck you can also just do typeof(string[])

Andrew Bezzub · Accepted Answer · 2010-03-22 15:04:17Z

23

You could use Reflections, here is a sample:

    Type mytype = typeof (int);

    Type listGenericType = typeof (List<>);

    Type list = listGenericType.MakeGenericType(mytype);

    ConstructorInfo ci = list.GetConstructor(new Type[] {});

    List<int> listInt = (List<int>)ci.Invoke(new object[] {});

answered Mar 22, 2010 at 15:04

Andrew Bezzub

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3 Comments

Harald Coppoolse Over a year ago

The problem is that we don't know the myType is typeof(int), so your last statement can't be List<int>, we would like something like Liar<myType>, but of course that can't be done. To create the instance we should use System.Activator.CreateInstance(myType). But then again, the return value if an object of type myType. And you have to use the System.Type to find out about the methods / properties / interfaces etc.

Andrew Bezzub Over a year ago

It can be done using generics: List<T> CreateMyList<T>(). Inside of this method you can do: Type myType = typeof(T); and then everything as above. You would be able to use method like this: List<int> list = CreateList<int>()

Bertie Over a year ago

Downvoted because the solution doesn't fit the problem. The issue is that 'T' isn't known, so even doing CreateMyList<T> isn't valid, because T is is most likely not available.

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