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csharp comment // The Delegate declaration which defines the signature of methods which can be invoked
csharp code public delegate void ScoreChangeEventHandler (int newScore, ref bool cancel);
csharp blank
csharp comment // Class which makes the event
csharp code public class Game {
csharp comment // Note the use of the event keyword
csharp code public event ScoreChangeEventHandler ScoreChange;
csharp blank
csharp code int score;
csharp blank
csharp comment // Score Property
csharp code public int Score {
csharp code get {
csharp code return score;
csharp code }
csharp code set {
csharp code if (score != value) {
csharp code bool cancel = false;
csharp code ScoreChange (value, ref cancel);
csharp code if (! cancel)
csharp code score = value;
csharp code }
csharp code }
csharp code }
csharp code }
csharp blank
csharp comment // Class which handles the event
csharp code public class Referee
csharp code {
csharp code public Referee (Game game) {
csharp comment // Monitor when a score changes in the game
csharp code game.ScoreChange += new ScoreChangeEventHandler (game_ScoreChange);
csharp code }
csharp blank
csharp comment // Notice how this method signature matches the ScoreChangeEventHandler's signature
csharp code private void game_ScoreChange (int newScore, ref bool cancel) {
csharp code if (newScore < 100)
csharp code System.Console.WriteLine ("Good Score");
csharp code else {
csharp code cancel = true;
csharp code System.Console.WriteLine ("No Score can be that high!");
csharp code }
csharp code }
csharp code }
csharp blank
csharp comment // Class to test it all
csharp code public class GameTest
csharp code {
csharp code public static void Main () {
csharp code Game game = new Game ();
csharp code Referee referee = new Referee (game);
csharp code game.Score = 70;
csharp code game.Score = 110;
csharp code }
csharp code }
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