How to: Query An Assembly's Metadata with Reflection (LINQ)

The following example shows how LINQ can be used with reflection to retrieve specific metadata about methods that match a specified search criterion. In this case, the query will find the names of all the methods in the assembly that return enumerable types such as arrays.

Example

Imports System.Reflection
Imports System.IO
Imports System.Linq
Module Module1

    Sub Main()
        Dim asmbly As Assembly = 
            Assembly.Load("System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken= b77a5c561934e089")

        Dim pubTypesQuery = From type In asmbly.GetTypes() 
                            Where type.IsPublic 
                            From method In type.GetMethods() 
                            Where method.ReturnType.IsArray = True 
                            Let name = method.ToString() 
                            Let typeName = type.ToString() 
                            Group name By typeName Into methodNames = Group


        Console.WriteLine("Getting ready to iterate")
        For Each item In pubTypesQuery
            Console.WriteLine(item.methodNames)

            For Each type In item.methodNames
                Console.WriteLine(" " & type)
            Next
        Next
        Console.ReadKey()
    End Sub

End Module

using System.Reflection;
using System.IO;
namespace LINQReflection
{
    class ReflectionHowTO
    {
        static void Main(string[] args)
        {
            Assembly assembly = Assembly.Load("System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken= b77a5c561934e089");
            var pubTypesQuery = from type in assembly.GetTypes()
                        where type.IsPublic
                            from method in type.GetMethods()
                            where method.ReturnType.IsArray == true 
                                || ( method.ReturnType.GetInterface(
                                    typeof(System.Collections.Generic.IEnumerable<>).FullName ) != null
                                && method.ReturnType.FullName != "System.String" )
                            group method.ToString() by type.ToString();

            foreach (var groupOfMethods in pubTypesQuery)
            {
                Console.WriteLine("Type: {0}", groupOfMethods.Key);
                foreach (var method in groupOfMethods)
                {
                    Console.WriteLine("  {0}", method);
                }
            }

            Console.WriteLine("Press any key to exit");
            Console.ReadKey();
        }
    }  
}

The example uses the GetTypes method to return an array of types in the specified assembly. The where filter is applied so that only public types are returned. For each public type, a subquery is generated by using the MethodInfo array that is returned from the GetMethods call. These results are filtered to return only those methods whose return type is an array or else a type that implements IEnumerable<T>. Finally, these results are grouped by using the type name as a key.

Compiling the Code

• Create a Visual Studio project that targets the .NET Framework version 3.5. The project has a reference to System.Core.dll and a using directive (C#) or Imports statement (Visual Basic) for the System.Linq namespace by default. In C# projects, add a using directive for the System.IO namespace.

• Copy this code into your project.

• Press F5 to compile and run the program.

• Press any key to exit the console window.

See Also

Concepts

LINQ to Objects