C generic list T how to get the type of T

Question

I m working on a reflection project  and now I m stuck   If I have an object of myclass that can hold a List lt SomeClass gt   does anyone know how to get the type as in the code below if the property myclass SomList is empty   List lt myclass gt  myList   dataGenerator getMyClasses    lbxObjects ItemsSource   myList   lbxObjects SelectionChanged    lbxObjects SelectionChanged   private void lbxObjects SelectionChanged object sender  SelectionChangedEventArgs e        Reflect       Private void Reflect         foreach  PropertyInfo pi in lbxObjects SelectedItem GetType   GetProperties                  switch  pi PropertyType Name ToLower                          case  list 1                                               This works if the List lt T gt  contains one or more elements                  Type tTemp   GetGenericType pi GetValue lbxObjects SelectedItem  null                        but how is it possible to get the Type if the value is null                      I need to be able to create a new object of the type the generic list expect                      Type type   pi getType      how to get the Type of the class inside List lt T gt                   break                                   private Type GetGenericType object obj        if  obj    null                Type t   obj GetType            if  t IsGenericType                        Type   at   t GetGenericArguments                t   at First lt Type gt                        return t            else               return null

User · Answer

Given an object which I suspect to be some kind of IList lt  gt   how can I determine of what it s an IList lt  gt    Here s a reliable solution  My apologies for length - C  s introspection API makes this suprisingly difficult        lt summary gt      Test if a type implements IList of T  and if so  determine T       lt  summary gt  public static bool TryListOfWhat Type type  out Type innerType        Contract Requires type    null        var interfaceTest   new Func lt Type  Type gt  i   gt  i IsGenericType  amp  amp  i GetGenericTypeDefinition      typeof IList lt  gt     i GetGenericArguments   Single     null        innerType   interfaceTest type       if  innerType    null                return true             foreach  var i in type GetInterfaces                  innerType   interfaceTest i           if  innerType    null                        return true                       return false      Example usage       object value   new ObservableCollection lt int gt     Type innerType  TryListOfWhat value GetType    out innerType  Dump    innerType Dump      Returns  True typeof Int32

User · Answer

Type type   pi PropertyType  if type IsGenericType  amp  amp  type GetGenericTypeDefinition              typeof List lt  gt          Type itemType   type GetGenericArguments   0      use this          More generally  to support any IList lt T gt   you need to check the interfaces   foreach  Type interfaceType in type GetInterfaces          if  interfaceType IsGenericType  amp  amp          interfaceType GetGenericTypeDefinition              typeof IList lt  gt                  Type itemType   type GetGenericArguments   0              do something            break

User · Answer

Marc s answer is the approach I use for this  but for simplicity  and a friendlier API   you can define a property in the collection base class if you have one such as   public abstract class CollectionBase lt T gt    IList lt T gt               public Type ElementType            get                  return typeof T                    I have found this approach useful  and is easy to understand for any newcomers to generics

User · Answer

Given an object which I suspect to be some kind of IList lt  gt   how can I determine of what it s an IList lt  gt    Here s the gutsy solution  It assumes you have the actual object to test  rather than a Type    public static Type ListOfWhat Object list        return ListOfWhat2  dynamic list      private static Type ListOfWhat2 lt T gt  IList lt T gt  list        return typeof T       Example usage   object value   new ObservableCollection lt DateTime gt     ListOfWhat value  Dump      Prints  typeof DateTime

[c#] C# generic list <T> how to get the type of T?

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