Let say I have a generic member in a class or method, so:
public class Foo<T>
{
public List<T> Bar { get; set; }
public void Baz()
{
// get type of T
}
}
When I instantiate the class, the T
becomes MyTypeObject1
, so the class has a generic list property: List<MyTypeObject1>
. The same applies to a generic method in a non-generic class:
public class Foo
{
public void Bar<T>()
{
var baz = new List<T>();
// get type of T
}
}
I would like to know, what type of objects the list of my class contains. So the list property called Bar
or the local variable baz
, contains what type of T
?
I cannot do Bar[0].GetType()
, because the list might contain zero elements. How can I do it?
Using 3dGrabber's solution:
public static T GetEnumeratedType<T>(this IEnumerable<T> _)
{
return default(T);
}
//and now
var list = new Dictionary<string, int>();
var stronglyTypedVar = list.GetEnumeratedType();
public bool IsCollection<T>(T value){
var valueType = value.GetType();
return valueType.IsArray() || typeof(IEnumerable<object>).IsAssignableFrom(valueType) || typeof(IEnumerable<T>).IsAssignableFrom(valuetype);
}
You can get the type of "T" from any collection type that implements IEnumerable<T> with the following:
public static Type GetCollectionItemType(Type collectionType)
{
var types = collectionType.GetInterfaces()
.Where(x => x.IsGenericType
&& x.GetGenericTypeDefinition() == typeof(IEnumerable<>))
.ToArray();
// Only support collections that implement IEnumerable<T> once.
return types.Length == 1 ? types[0].GetGenericArguments()[0] : null;
}
Note that it doesn't support collection types that implement IEnumerable<T> twice, e.g.
public class WierdCustomType : IEnumerable<int>, IEnumerable<string> { ... }
I suppose you could return an array of types if you needed to support this...
Also, you might also want to cache the result per collection type if you're doing this a lot (e.g. in a loop).
Try
list.GetType().GetGenericArguments()
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;
}
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.
Consider this: I use it to export 20 typed list by same way:
private void Generate<T>()
{
T item = (T)Activator.CreateInstance(typeof(T));
((T)item as DemomigrItemList).Initialize();
Type type = ((T)item as DemomigrItemList).AsEnumerable().FirstOrDefault().GetType();
if (type == null) return;
if (type != typeof(account)) //account is listitem in List<account>
{
((T)item as DemomigrItemList).CreateCSV(type);
}
}
That's work for me. Where myList is some unknown kind of list.
IEnumerable myEnum = myList as IEnumerable;
Type entryType = myEnum.AsQueryable().ElementType;
(note: I'm assuming that all you know is object
or IList
or similar, and that the list could be any type at runtime)
If you know it is a List<T>
, then:
Type type = abc.GetType().GetGenericArguments()[0];
Another option is to look at the indexer:
Type type = abc.GetType().GetProperty("Item").PropertyType;
Using new TypeInfo:
using System.Reflection;
// ...
var type = abc.GetType().GetTypeInfo().GenericTypeArguments[0];
This is how i did it
internal static Type GetElementType(this Type type)
{
//use type.GenericTypeArguments if exist
if (type.GenericTypeArguments.Any())
return type.GenericTypeArguments.First();
return type.GetRuntimeProperty("Item").PropertyType);
}
Then call it like this
var item = Activator.CreateInstance(iListType.GetElementType());
OR
var item = Activator.CreateInstance(Bar.GetType().GetElementType());
If you want to know a property's underlying type, try this:
propInfo.PropertyType.UnderlyingSystemType.GenericTypeArguments[0]
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();
Type:
type = list.AsEnumerable().SingleOrDefault().GetType();
With the following extension method you can get away without reflection:
public static Type GetListType<T>(this List<T> _)
{
return typeof(T);
}
Or more general:
public static Type GetEnumeratedType<T>(this IEnumerable<T> _)
{
return typeof(T);
}
Usage:
List<string> list = new List<string> { "a", "b", "c" };
IEnumerable<string> strings = list;
IEnumerable<object> objects = list;
Type listType = list.GetListType(); // string
Type stringsType = strings.GetEnumeratedType(); // string
Type objectsType = objects.GetEnumeratedType(); // BEWARE: object
If you dont need the whole Type variable and just want to check the type you can easily create a temp variable and use is operator.
T checkType = default(T);
if (checkType is MyClass)
{}
Source: Stackoverflow.com