Reflection allows viewing metadata and dynamically invoking methods of classes at runtime. It allows discovering and using new classes without recompiling. Key reflection types include System.Type, System.Reflection.Assembly, and MemberInfo. The Type object provides metadata like methods and properties. Assembly loads metadata for a DLL. MemberInfo is the base for method and property metadata. Reflection is used for documentation, plugins, adaptive solutions, and converting scripts to compiled code.

1. Reflecting on the CodeDom

2. What is Reflection? Allows you to view metadata about classes Allows you to dynamically discover new classes at runtime Allows you to dynamically invoke methods or properties discovered at runtime Allows you to create new types at runtime

3. Why should we care about Reflection? Viewing metadata allows us to automate documentation Dynamically discovering classes make it easier to create plug-ins Dynamically invoking new methods allows us to create adaptive solutions not dependant on recompiling Creating new types at runtime allows us to convert scripting customizations to compiled code

4. A Gentle Tour of Reflection Key data types System.Type System.Reflection.Assembly System.Reflection.MemberInfo System.Reflection.MethodInfo System.Reflection.ConstructorInfo System.Reflection.ProperyInfo System.Reflection.EventInfo

5. The Great and Mighty Type Object Every Object provides a GetType method which will return a Type Object Key Properties include: Assembly will return the Assembly object where this type is located BaseType will return the Type object that this Type is directly derived IsClass, IsEnum, IsInterface will provide details about the type of class

6. Type Object (Contd) Key Methods include: GetMethods will return an array of MethodInfo objects one for each method defined in the Type GetProperties will return an array of PropertyInfo objects one for each property defined in the Type GetEvents will return an array of EventInfo objects one for each event defined in the Type GetConstructors will return an array of ConstructorInfo objects one for each event defined in the Type

7. Assembly Object Provides metadata information about a DLL Key methods GetTypes will return an array of Type objects one for each type included in the assembly Key static methods Load will return the assembly specified LoadFrom will return the assembly specified by filename

8. MemberInfo Base Class for MethodInfo, ConstructorInfo, ProperyInfo, EventInfo Provides limited baseline common attributes such as: Name MemberType

9. Sample Code (Object Browser) Select a DLL Detect all of the Classes Detect all of the Properties Detect all of the Methods Detect all of the Parameters for each Method

10. Commenting Code Type Custom Attributes Apply Custom Attributes to your code Use Reflection to retrieve the custom attributes from the Types in an Assembly

11. Defining a Custom Attribute AttributeUsageAttribute Define where an attribute can be used Specify whether or not the attribute can be applied more than once Specify whether or not the attribute is inheritable Derives from System.Attribute Define a Constructor to be called when an attribute is added to code Define properties to expose attribute specific details

12. Applying Attributes to Code C# [FlowerBoxAttribute (&quot;Nick Harrison&quot;, “July 7, 2004&quot;, &quot;A simple class to do some simple calcs&quot;)] VB.Net <FlowerBoxAttribute(&quot;Nick Harrison&quot;, “July 7, 2004&quot;, &quot;A simple class to do some simple calcs&quot;)>

13. Retrieving Attributes from Code FlowerBoxAttribute [] FlowerBoxes; FlowerBoxes = (FlowerBoxAttribute []) Member.GetCustomAttributes (typeof (FlowerBoxAttribute ), false); foreach (CustomAttributes.FlowerBoxAttribute FlowerBox in FlowerBoxes) { // Access the properties of the FlowerBoxAttribute }

14. Creating a Plug-in Store the location of the Assembly in a config file Store the name of the Class in a config file Load the Assembly Instantiate the Type Convert the new type to a pre-defined interface. Use the new interface object

15. CodeDom Demystified