How to get the type of T from a member of a generic class or method?

Question

Let say I have a generic member in a class or method, so:

public class Foo
{
    public List Bar { get; set; }

    public void Baz()
    {         


        

Answer 1

You can use this one for return type of generic list:

public string ListType<T>(T value)
{
    var valueType = value.GetType().GenericTypeArguments[0].FullName;
    return valueType;
}

Answer 2

The GetGenericArgument() method has to be set on the Base Type of your instance (whose class is a generic class myClass<T>). Otherwise, it returns a type[0]

Example:

Myclass<T> instance = new Myclass<T>();
Type[] listTypes = typeof(instance).BaseType.GetGenericArguments();

Answer 3

public bool IsCollection<T>(T value){
  var valueType = value.GetType();
  return valueType.IsArray() || typeof(IEnumerable<object>).IsAssignableFrom(valueType) || typeof(IEnumerable<T>).IsAssignableFrom(valuetype);
}

Answer 4

Type:

type = list.AsEnumerable().SingleOrDefault().GetType();

Answer 5

If you want to know a property's underlying type, try this:

propInfo.PropertyType.UnderlyingSystemType.GenericTypeArguments[0]

Answer 6

I use this extension method to accomplish something similar:

public static string GetFriendlyTypeName(this Type t)
{
    var typeName = t.Name.StripStartingWith("`");
    var genericArgs = t.GetGenericArguments();
    if (genericArgs.Length > 0)
    {
        typeName += "<";
        foreach (var genericArg in genericArgs)
        {
            typeName += genericArg.GetFriendlyTypeName() + ", ";
        }
        typeName = typeName.TrimEnd(',', ' ') + ">";
    }
    return typeName;
}

public static string StripStartingWith(this string s, string stripAfter)
{
    if (s == null)
    {
        return null;
    }
    var indexOf = s.IndexOf(stripAfter, StringComparison.Ordinal);
    if (indexOf > -1)
    {
        return s.Substring(0, indexOf);
    }
    return s;
}

You use it like this:

[TestMethod]
public void GetFriendlyTypeName_ShouldHandleReallyComplexTypes()
{
    typeof(Dictionary<string, Dictionary<string, object>>).GetFriendlyTypeName()
        .ShouldEqual("Dictionary<String, Dictionary<String, Object>>");
}

This isn't quite what you're looking for, but it's helpful in demonstrating the techniques involved.