1C:\Users\Jim Whitehead\Documents\Visual ...\SimpleDelegateExample\Program.csusing System;using System.Collections.Generic;using System.Linq;using System.Text;namespace SimpleDelegateExample{ class Subject { // Create delegate type "notifier" public delegate void notifier(string message); // Create instance of "notifier" type, called myNotifier public notifier myNotifier; public string subjectContents; public string SubjectContents { get { return subjectContents; } // Set accessor. First sets the value of the Subjet's string (subjectContents), // then notifies listeners by calling the delegate myNotifier. All listeners // that have registered with Subject (by adding a method to myNotifier) are // called. set { subjectContents = value; // Check to see that there is at least one method in the delegate instance // then call the delegate (i.e., call all methods referenced in the delegate) if (myNotifier != null) { myNotifier(value); } } } } class Observer { public string observername; // Constructor // Saves the name of the observer (we use this in printed output when we receive a notification) // Adds receive_notification method to myNotifier delegate instance found in subject public Observer(string name, Subject subject) { observername = name; subject.myNotifier += receive_notification; } public void receive_notification(string message) { System.Console.WriteLine("{0}: received notification: {1}", observername, message); } public void subscribe(Subject subject) {2C:\Users\Jim Whitehead\Documents\Visual ...\SimpleDelegateExample\Program.cs subject.myNotifier += receive_notification; } public void unsubscribe(Subject subject) { subject.myNotifier -= receive_notification; } } // class Program { static void Main(string[] args) { Subject mySubject = new Subject(); Observer bob = new Observer("Bob", mySubject); Observer alice = new Observer("Alice", mySubject); // Just create reference for now, will create instance later Observer maria; Subject secondSubject; mySubject.SubjectContents = "Hello, eventful world!"; System.Console.WriteLine(); mySubject.SubjectContents = "Oooh, baby!"; System.Console.WriteLine(); // Create new Observer, maria, and unsubscribe bob. maria = new Observer("Maria", mySubject); bob.unsubscribe(mySubject); mySubject.SubjectContents = "Who can it be now?"; System.Console.WriteLine(); // Create second Subject, and have Observers subscribe to it secondSubject = new Subject(); bob.subscribe(secondSubject); alice.subscribe(secondSubject); maria.subscribe(secondSubject); secondSubject.SubjectContents = "Hello, I am the second Subject"; System.Console.WriteLine(); mySubject.SubjectContents = "First subject here"; System.Console.WriteLine("That's all folks"); }
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