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MethodInfo.MakeGenericMethod Method

Note: This method is new in the .NET Framework version 2.0.

Substitutes the elements of an array of types for the type parameters of the current generic method definition, and returns a MethodInfo object representing the resulting constructed method.

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

public virtual MethodInfo MakeGenericMethod (
	params Type[] typeArguments
)
public MethodInfo MakeGenericMethod (
	Type[] typeArguments
)
public function MakeGenericMethod (
	... typeArguments : Type[]
) : MethodInfo

Parameters

typeArguments

An array of types to be substituted for the type parameters of the current generic method definition.

Return Value

A MethodInfo object that represents the constructed method formed by substituting the elements of typeArguments for the type parameters of the current generic method definition.

Exception typeCondition

InvalidOperationException

The current MethodInfo does not represent a generic method definition. That is, IsGenericMethodDefinition returns false.

ArgumentNullException

typeArguments is a null reference (Nothing in Visual Basic).

-or-

Any element of typeArguments is a null reference (Nothing in Visual Basic).

ArgumentException

The number of elements in typeArguments is not the same as the number of type parameters of the current generic method definition.

-or-

An element of typeArguments does not satisfy the constraints specified for the corresponding type parameter of the current generic method definition.

The MakeGenericMethod method allows you to write code that assigns specific types to the type parameters of a generic method definition, thus creating a MethodInfo object that represents a particular constructed method. If the ContainsGenericParameters property of this MethodInfo object returns true, you can use it to invoke the method or to create a delegate to invoke the method.

Methods constructed with the MakeGenericMethod method can be open, that is, some of their type arguments can be type parameters of enclosing generic types. You might use such open constructed methods when you generate dynamic assemblies. For example, consider the following C#, Visual Basic, and C++ code.

class C
{
    T N<T,U>(T t, U u) {...}
    public V M<V>(V v)
    {
        return N<V,int>(v, 42);
    }
}

Class C
    Public Function N(Of T,U)(ByVal ta As T, ByVal ua As U) As T
        ...
    End Function
    Public Function M(Of V)(ByVal va As V ) As V
        Return N(Of V, Integer)(va, 42)
    End Function
End Class

ref class C
{
private:
    generic <typename T, typename U> T N(T t, U u) {...}
public:
    generic <typename V> V M(V v)
    {
        return N<V, int>(v, 42);
    }
};

The method body of M contains a call to method N, specifying the type parameter of M and the type Int32. The IsGenericMethodDefinition property returns false for method N<V,int>. The ContainsGenericParameters property returns true, so method N<V,int> cannot be invoked.

For a list of the invariant conditions for terms specific to generic methods, see the IsGenericMethod property. For a list of the invariant conditions for other terms used in generic reflection, see the IsGenericType property.

The following code example demonstrates the properties and methods of MethodInfo that support the examination of generic methods. The example does the following:

  • Defines a class that has a generic method.

  • Creates a MethodInfo that represents the generic method.

  • Displays properties of the generic method definition.

  • Assigns type arguments to the type parameters of the MethodInfo, and invokes the resulting constructed generic method.

  • Displays properties of the constructed generic method.

  • Retrieves the generic method definition from the constructed method and compares it to the original definition.

using System;
using System.Reflection;

// Define a class with a generic method.
public class Example
{
    public static void Generic<T>(T toDisplay)
    {
        Console.WriteLine("\r\nHere it is: {0}", toDisplay);
    }
}

public class Test
{
    public static void Main()
    {
        Console.WriteLine("\r\n--- Examine a generic method.");

        // Create a Type object representing class Example, and
        // get a MethodInfo representing the generic method.
        //
        Type ex = typeof(Example);
        MethodInfo mi = ex.GetMethod("Generic");

        DisplayGenericMethodInfo(mi);

        // Assign the int type to the type parameter of the Example 
        // method.
        //
        MethodInfo miConstructed = mi.MakeGenericMethod(typeof(int));

        DisplayGenericMethodInfo(miConstructed);

        // Invoke the method.
        object[] args = {42};
        miConstructed.Invoke(null, args);

        // Invoke the method normally.
        Example.Generic<int>(42);

        // Get the generic type definition from the closed method,
        // and show it's the same as the original definition.
        //
        MethodInfo miDef = miConstructed.GetGenericMethodDefinition();
        Console.WriteLine("\r\nThe definition is the same: {0}",
            miDef == mi);
    }
        
    private static void DisplayGenericMethodInfo(MethodInfo mi)
    {
        Console.WriteLine("\r\n{0}", mi);

        Console.WriteLine("\tIs this a generic method definition? {0}", 
            mi.IsGenericMethodDefinition);

        Console.WriteLine("\tIs it a generic method? {0}", 
            mi.IsGenericMethod);

        Console.WriteLine("\tDoes it have unassigned generic parameters? {0}", 
            mi.ContainsGenericParameters);

        // If this is a generic method, display its type arguments.
        //
        if (mi.IsGenericMethod)
        {
            Type[] typeArguments = mi.GetGenericArguments();

            Console.WriteLine("\tList type arguments ({0}):", 
                typeArguments.Length);

            foreach (Type tParam in typeArguments)
            {
                // IsGenericParameter is true only for generic type
                // parameters.
                //
                if (tParam.IsGenericParameter)
                {
                    Console.WriteLine("\t\t{0}  parameter position {1}" +
                        "\n\t\t   declaring method: {2}",
                        tParam,
                        tParam.GenericParameterPosition,
                        tParam.DeclaringMethod);
                }
                else
                {
                    Console.WriteLine("\t\t{0}", tParam);
                }
            }
        }
    }
}

/* This example produces the following output:

--- Examine a generic method.

Void Generic[T](T)
        Is this a generic method definition? True
        Is it a generic method? True
        Does it have unassigned generic parameters? True
        List type arguments (1):
                T  parameter position 0
                   declaring method: Void Generic[T](T)

Void Generic[Int32](Int32)
        Is this a generic method definition? False
        Is it a generic method? True
        Does it have unassigned generic parameters? False
        List type arguments (1):
                System.Int32

Here it is: 42

Here it is: 42

The definition is the same: True

 */

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

.NET Compact Framework

Supported in: 2.0

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