MSDN Magazine - January 2008 - (Page 33)

Reflection and Generics KEN GETZ K nowing that I love to play with such things, a friend recently asked me to help write a simple tool that could export to Microsoft® Excel® a sortable list of all the members of a new assembly that she was required to document. The tool needed to provide information about the properties, methods, events, and interfaces, and list all the parameters for each of the members. Having played with reflection before, it seemed like fun. As I began, though, I kept finding member names that were formatted oddly. For example, using my program to list out the contents of the mscorlib assembly, I found names like Dictionary`2 and ReadOnlyCollection`1. It turns out that names like those exist for a reason. The Microsoft .NET Framework exposes information about generic types and methods differently than it does for those that are non-generic. This realization led me to investigate—and now document—reflection features as they relate to generics. While generics are new as of the .NET Framework 2.0, using reflection to investigate and fabricate or call generic types and methods isn’t terribly difficult. My sample application (available from the MSDN® Magazine Web Figure 1 Classes in TestClasses.vb Public Class GenericClass(Of T) ‘ This is not a generic method. Public Sub Swap(ByRef item1 As T, ByRef item2 As T) Dim temp As T = item1 item2 = item1 item1 = temp End Sub ‘ This is a generic method and a generic method definition. Public Sub Swap(Of U)(ByRef item1 As U, ByRef item2 As U) Dim temp As U = item1 item2 = item1 item1 = temp End Sub Public Function GenericMethod(Of M)(ByVal item1 As M) As String Return String.Format(“You passed in: {0}”, item1) End Function End Class Public Class BaseClass(Of T, U) Public Items As New Dictionary(Of T, U) Public Sub New() Debug.Print(“In BaseClass, GetType(T) = “ & GetType(T).Name) Debug.Print(“In BaseClass, GetType(U) = “ & GetType(U).Name) End Sub End Class site) shows off as many of the features exposed at the intersection of generics and reflection as I could discuss. If generics are completely new to you, see “Overview of Generics in the .NET Framework” at msdn2.microsoft.com/ms172193. Most importantly, review the terms described in the article because my goal is to show you how to extend existing reflection-based applications to handle generic types and methods. Beginning the Investigation Given an assembly, you can easily use reflection to investigate its members. You will need to use the Type.IsGenericType property to learn whether each type is generic in order to later create an instance of it. In my sample, the TestForGenericType procedure loads the contents of the mscorlib assembly and displays information about all the public generic types: Dim asm As Assembly = Assembly.ReflectionOnlyLoad(“mscorlib”) For Each typ As Type In asm.GetTypes() If typ.IsPublic AndAlso typ.IsGenericType Then AddToResults(typ.Name) End If Next The .NET Framework exposes information about generic types and methods differently than it does for those that are non-generic. In the sample, the AddToResults method and the DisplayResults method (not shown here) simply build output text and display it in an alert. So that you can investigate types that you created, the sample also includes a TestClasses.vb file that contains several sample classes, as shown in Figure 1. TestForGenericType continues by testing these three classes: AddToResults(“GenericClass(Of Integer) is generic: {0}”, _ GetType(GenericClass(Of Integer)).IsGenericType) AddToResults(“NonGenericClass is generic: {0}”, _ GetType(NonGenericClass).IsGenericType) AddToResults( _ “BaseClass(Of Integer, String) is generic: {0}”, _ GetType(BaseClass(Of Integer, String)). _ IsGenericType) This code creates constructed versions of each of the generic types shown previously. (A constructed type is a generic type for which you’ve supplied specifics for each placeholder type.) GenericClass and BaseClass are generic types, whereas NonGenericClass is not. Note that when the .NET Framework returns the Name property of january2008 33 http://msdn2.microsoft.com/ms172193

Table of Contents Feed for the Digital Edition of MSDN Magazine - January 2008

MSDN Magazine - January 2008 Contents Toolbox CLR Inside Out Data Points Advanced Basics Cutting Edge IIS 7.0 - Enhance Your Apps with the Integrated ASP.NET Pipeline World Ready - Around the World with ASP.NET AJAX Applications WCF Syndication - HTTP Programming with WCF and the .NET Framework 3.5 Wicked Code Foundations Extreme ASP.NET {End Bracket}

MSDN Magazine - January 2008

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