Beginning C# 2008-from Novice-to-professional - A2Z Dotnet

CHAPTER 9 ■ LEARNING ABOUT LISTS, DELEGATES, AND LAMBDA EXPRESSIONS 241A delegate and interface share the same role, in that they are types without implementationsand are used to build components. An interface can have multiple methods and properties.A delegate is a method declaration and can define only the parameters and return types. Thepurpose of delegates is to be able to define a generic method-calling mechanism without needingto add the baggage of implementing an interface.The approach used in the delegate solution to the problem presented in the previous sectionis to define a chunk of functionality that performs the iteration, called an iterator. Andthen to do something with the iteration, another chunk of functionality is integrated via a delegate.The result is that you have two separate pieces of functionality that are integrated usinga component methodology.Following is the complete rewritten foreach code that uses delegates.public delegate void ProcessValue(int value);public static class Extensions {public static void Iterate(this ICollection collection,ProcessValue cb) {foreach (int element in collection) {cb(element);}}}static class Tests {static int _runningTotal;static void ProcessRunningTotal(int value) {_runningTotal += value;}static int _maxValue;static void ProcessMaximumValue(int value) {if (value > _maxValue) {_maxValue = value;}}static void DoRunningTotalAndMaximum() {List lst = new List { 1, 2, 3, 4 };_runningTotal = 0;lst.Iterate(new ProcessValue(ProcessRunningTotal));Console.WriteLine("Running total is (" + _runningTotal + ")");}_maxValue = int.MinValue;lst.Iterate(new ProcessValue(ProcessMaximumValue));Console.WriteLine("Maximum value is (" + _maxValue + ")");