vb net 2d barcode generator Part IV in .NET

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for (Int32 m = 0; m < map.InterfaceMethods.Length; m++) { // Display the interface method name and which // type method implements the interface method. Console.WriteLine(" {0} is implemented by {1}", map.InterfaceMethods[m], map.TargetMethods[m]); } }

// Returns true if type matches filter criteria private static Boolean TypeFilter(Type t, Object filterCriteria) { // Return true if the interface is defined in assembly identified by filterCriteria return t.Assembly == filterCriteria; } }

When you build and run the code above, you get the following output:

MyRetailer implements the following interfaces (defined in this assembly): Interface: IBookRetailer Void Purchase() is implemented by Void IBookRetailer.Purchase() Void ApplyDiscount() is implemented by Void ApplyDiscount() Interface: IMusicRetailer Void Purchase() is implemented by Void IMusicRetailer.Purchase()

Note that the IDisposable interface does not appear in the output because this interface is not declared in the EXE file s assembly .

Now that you know how to discover the members defined by a type, you may want to invoke one of these members . What invoke means depends on the kind of member being invoked . Invoking a FieldInfo lets you get or set a field s value, invoking a ConstructorInfo lets you create an instance of the type passing arguments to a constructor, invoking a MethodInfo lets you call a method passing arguments and obtaining its return value, invoking a PropertyInfo lets you call the property s get or set accessor method, and invoking an EventInfo lets you add or remove an event handler . Let s discuss how to invoke a method first because this is the most complex member you can invoke . Then we ll discuss how to invoke the other members . The Type class offers an InvokeMember method that lets you invoke a member . There are several overloaded versions of InvokeMember . I ll discuss one of the more common overloads; the other overloads work similarly .

public abstract class Type : MemberInfo, ... { public Object InvokeMember( String name, // Name of member BindingFlags invokeAttr, // How to look up members Binder binder, // How to match members and arguments Object target, // Object to invoke member on Object[] args, // Arguments to pass to method CultureInfo culture); // Culture used by some binders ... }

When you call InvokeMember, it searches the type s members for a match . If no match is found, a System.MissingMethodException, System.MissingFieldException, or System.MissingMemberException exception is thrown . If a match is found, InvokeMember invokes the member . If the member returns something, InvokeMember returns it to you . If the member doesn t return anything, InvokeMember returns null . If the member you call throws an exception, InvokeMember catches the exception and throws a new System.Reflection. TargetInvocationException . The TargetInvocationException object s InnerException property will contain the actual exception that the invoked method threw . Personally, I don t like this behavior . I d prefer it if InvokeMember didn t wrap the exception and just allowed it to come through . Internally, InvokeMember performs two operations . First, it must select the appropriate member to be called this is known as binding . Second, it must actually invoke the member this is known as invoking . When you call InvokeMember, you pass a string as the name parameter, indicating the name of the member you want InvokeMember to bind to . However, the type might offer several members with the same name . After all, there might be several overloaded versions of a method, or a method and a field might have the same name . Of course, InvokeMember must bind to a single member before it can invoke it . All of the parameters passed to InvokeMember (except for the target parameter) are used to help InvokeMember decide which member to bind to . Let s take a closer look at these parameters . The binder parameter identifies an object whose type is derived from the abstract System.Reflection.Binder type . A Binder-derived type is a type that encapsulates the rules for how InvokeMember should select a single member . The Binder base type defines abstract virtual methods such as BindToField, BindToMethod, ChangeType, ReorderArgumentArray, SelectMethod, and SelectProperty . Internally, InvokeMember calls these methods by using the Binder object passed via InvokeMember s binder parameter . Microsoft has defined an internal (undocumented) concrete type, called System. DefaultBinder, which is derived from Binder . This DefaultBinder type ships with the FCL, and Microsoft expects that almost everyone will use this binder . Some compiler vendors will define their own Binder-derived type and ship it in a runtime library used by code emitted by their compiler .1 When you pass null to InvokeMember s binder parameter, it will use a

The code that accompanies this book includes the source code for a SimpleBinder class that demonstrates how to define your own Binder-derived type .