MSDN Magazine - January 2008 - (Page 35)

Again, this sample is operating on the generic type definition: Public Function GenericMethod(Of M)(ByVal item1 As M) As String Return String.Format(“You passed in: {0}”, item1) End Function And by calling the MakeGenericMethod method, passing in the Integer type, the code then proceeds to create the following generic method at run time (item1 represents the type you’ve passed in from the calling code): Public Function GenericMethod (ByVal item1 As Integer) As String Return String.Format(“You passed in: {0}”, item1) End Function Creating Generic Type Instances and Calling Methods Assuming that one of your goals is to be able to create an instance of a generic type and perhaps to call a constructed generic method, you’ll need a few more techniques. In order to create an instance of a type, there can’t be generic type definitions or generic method definitions with unsatisfied type placeholders anywhere in the entire chain of dependencies for the type. Generic types for which all the type placeholders have been specified are called closed generic types (the same terminology applies to methods). You can only create an instance of a closed generic type, and you can only invoke a closed generic method. But what if you’re handed a generic type that has a complex inheritance hierarchy? How can you be sure there aren’t any open types in the type’s ancestry? To determine this, you can retrieve the Type.ContainsGenericParameters property, which indicates definitively if you’re working with a closed or open generic type: if the property returns True, you’ll know you have an Generic types for which all open generic type, and you the type placeholders have won’t be able to create an instance of it. The TestForOpenOrclosed generic types. ClosedGeneric procedure demonstrates this behavior using two classes in the TestClasses file, which are shown here: Public Class BaseClass(Of T, U) Public Items As New Dictionary(Of T, U) End Class Public Class DerivedClass(Of V) Inherits BaseClass(Of Integer, V) End Class The TestForOpenOrClosedGeneric procedure calls the DisplayGenericTypeInfo procedure in Figure 3, displaying information about several different types. Given a type, the DisplayGenericTypeInfo procedure first displays the type name, whether the type is a generic type definition, and whether it’s a generic type. Next, it displays whether the type contains generic parameters (if it’s a generic type definition, it contains Advanced Document Imaging Toolkits Our .NET imaging components are designed exclusively for the Microsoft .NET Framework, offering developers Photographic and Document imaging for web and windows based applications featuring AJAX-enabled web imaging, PDF support, data capture, scanning/OCR, barcode reading systems, image management, and archiving. Advanced technology to power your applications. Visit Atalasoft.com for a free trial download. Atalasoft, Your .NET Imaging Partner Call us toll free at 866-568-0129 www.atalasoft.com Advanced Basics january2008 35 http://www.atalasoft.com http://www.atalasoft.com

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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