Type.GetGenericTypeDefinition Method

July 28, 2014

Returns a Type object that represents a generic type definition from which the current generic type can be constructed.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public virtual Type GetGenericTypeDefinition()

Return Value

Type: System.Type
A Type object representing a generic type from which the current type can be constructed.

ExceptionCondition
InvalidOperationException

The current type is not a generic type. That is, IsGenericType returns false.

NotSupportedException

The invoked method is not supported in the base class. Derived classes must provide an implementation.

A generic type definition is a template from which other types can be constructed. For example, from the generic type definition G<T> (expressed in C# syntax; G(Of T) in Visual Basic or generic <typename T> ref class G in C++) you can construct and instantiate the type G<int> (G(Of Integer) in Visual Basic). Given a Type object representing this constructed type, the GetGenericTypeDefinition method returns the generic type definition.

If two constructed types are created from the same generic type definition, using the same type arguments, the GetGenericTypeDefinition method returns the same Type object for both types.

If you call the GetGenericTypeDefinition method on a Type object that already represents a generic type definition, it returns the current Type.

Important noteImportant Note:

An array of generic types is not itself generic. In the C# code A<int>[] v; or the Visual Basic code Dim v() As A(Of Integer), the type of variable v is not generic. Use IsGenericType to determine whether a type is generic before calling GetGenericTypeDefinition.

For a list of the invariant conditions for terms used in generic reflection, see the IsGenericType property remarks.

The following code example creates an instance of a constructed type by using ordinary instance creation and then uses the GetType and GetGenericTypeDefinition methods to retrieve the constructed type and the generic type definition. This example uses the generic Dictionary<TKey, TValue> type; the constructed type represents a Dictionary<TKey, TValue> of Test objects with string keys.


using System;
using System.Reflection;
using System.Collections.Generic;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      outputBlock.Text += "\r\n--- Get the generic type that defines a constructed type." + "\n";

      // Create a Dictionary of Example objects, using strings for the
      // keys.       
      Dictionary<string, Example> d = new Dictionary<string, Example>();

      // Get a Type object representing the constructed type.
      //
      Type constructed = d.GetType();
      DisplayTypeInfo(outputBlock, constructed);

      Type generic = constructed.GetGenericTypeDefinition();
      DisplayTypeInfo(outputBlock, generic);
   }

   private static void DisplayTypeInfo(System.Windows.Controls.TextBlock outputBlock, Type t)
   {
      outputBlock.Text += String.Format("\r\n{0}", t) + "\n";
      outputBlock.Text += String.Format("\tIs this a generic type definition? {0}",
          t.IsGenericTypeDefinition) + "\n";
      outputBlock.Text += String.Format("\tIs it a generic type? {0}",
          t.IsGenericType) + "\n";
      Type[] typeArguments = t.GetGenericArguments();
      outputBlock.Text += String.Format("\tList type arguments ({0}):", typeArguments.Length) + "\n";
      foreach (Type tParam in typeArguments)
      {
         outputBlock.Text += String.Format("\t\t{0}", tParam) + "\n";
      }
   }
}

/* This example produces the following output:

--- Get the generic type that defines a constructed type.

System.Collections.Generic.Dictionary`2[System.String,Test]
        Is this a generic type definition? False
        Is it a generic type? True
        List type arguments (2):
                System.String
                Test

System.Collections.Generic.Dictionary`2[TKey,TValue]
        Is this a generic type definition? True
        Is it a generic type? True
        List type arguments (2):
                TKey
                TValue
 */


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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