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 lt T gt        public List lt T gt  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 lt MyTypeObject1 gt   The same applies to a generic method in a non-generic class   public class Foo       public void Bar lt T gt                  var baz   new List lt T gt                 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

User · Answer

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 lt T gt   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

User · Answer

Using 3dGrabber s solution   public static T GetEnumeratedType lt T gt  this IEnumerable lt T gt           return default T        and now   var list   new Dictionary lt string  int gt     var stronglyTypedVar   list GetEnumeratedType

User · Answer

Try  list GetType   GetGenericArguments

User · Answer

You can use this one for return type of generic list   public string ListType lt T gt  T value        var valueType   value GetType   GenericTypeArguments 0  FullName      return valueType

User · Answer

The GetGenericArgument   method has to be set on the Base Type of your instance   whose class is a generic class myClass lt T gt    Otherwise  it returns a type 0   Example   Myclass lt T gt  instance   new Myclass lt T gt     Type   listTypes   typeof instance  BaseType GetGenericArguments

User · Answer

With the following extension method you can get away without reflection   public static Type GetListType lt T gt  this List lt T gt           return typeof T       Or more general   public static Type GetEnumeratedType lt T gt  this IEnumerable lt T gt           return typeof T       Usage   List lt string gt         list      new List lt string gt     a    b    c     IEnumerable lt string gt  strings   list  IEnumerable lt object gt  objects   list   Type listType      list GetListType                 string Type stringsType   strings GetEnumeratedType        string Type objectsType   objects GetEnumeratedType        BEWARE  object

User · Answer

If I understand correctly  your list has the same type parameter as the container class itself  If this is the case  then   Type typeParameterType   typeof T     If you are in the lucky situation of having object as a type parameter  see Marc s answer

User · Answer

That s work for me  Where myList is some unknown kind of list   IEnumerable myEnum   myList as IEnumerable  Type entryType   myEnum AsQueryable   ElementType

User · Answer

public bool IsCollection lt T gt  T value     var valueType   value GetType      return valueType IsArray      typeof IEnumerable lt object gt   IsAssignableFrom valueType     typeof IEnumerable lt T gt   IsAssignableFrom valuetype

User · Answer

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

User · Answer

Type   type   list AsEnumerable   SingleOrDefault   GetType

User · Answer

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

User · Answer

You can get the type of  T  from any collection type that implements IEnumerable lt T gt  with the following   public static Type GetCollectionItemType Type collectionType        var types   collectionType GetInterfaces            Where x   gt  x IsGenericType               amp  amp  x GetGenericTypeDefinition      typeof IEnumerable lt  gt             ToArray           Only support collections that implement IEnumerable lt T gt  once      return types Length    1   types 0  GetGenericArguments   0    null      Note that it doesn t support collection types that implement IEnumerable lt T gt  twice  e g    public class WierdCustomType   IEnumerable lt int gt   IEnumerable lt string gt            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

User · Answer

If you want to know a property s underlying type  try this   propInfo PropertyType UnderlyingSystemType GenericTypeArguments 0

User · Answer

Consider this  I use it to export 20 typed list by same way   private void Generate lt T gt          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 lt account gt                  T item as DemomigrItemList  CreateCSV type

User · Answer

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  gt  0                typeName      lt            foreach  var genericArg in genericArgs                        typeName    genericArg GetFriendlyTypeName                             typeName   typeName TrimEnd               gt              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  gt  -1                return s Substring 0  indexOf             return s      You use it like this    TestMethod  public void GetFriendlyTypeName ShouldHandleReallyComplexTypes         typeof Dictionary lt string  Dictionary lt string  object gt  gt   GetFriendlyTypeName            ShouldEqual  Dictionary lt String  Dictionary lt String  Object gt  gt         This isn t quite what you re looking for  but it s helpful in demonstrating the techniques involved

[c#] How to get the type of T from a member of a generic class or method?

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