C# in Depth

Saying goodbye to awkward delegate syntax139Likewise it’s undeniably ugly to write methods that are so simple that their implementationis shorter than their signature, solely because delegates need to have codeto execute and that code has to be in the form of a method. It adds an extra layer ofindirection between the code creating the delegate instance and the code that shouldexecute when the delegate instance is invoked. Often extra layers of indirection arewelcome—and of course that option hasn’t been removed in C# 2—but at the sametime it often makes the code harder to read, and pollutes the class with a bunch ofmethods that are only used for delegates.Unsurprisingly, all of these are improved greatly in C# 2. The syntax can still occasionallybe wordier than we might like (which is where lambda expressions come intoplay in C# 3), but the difference is significant. To illustrate the pain, we’ll start withsome code in C# 1 and improve it in the next couple of sections. Listing 5.1 builds a(very) simple form with a button and subscribes to three of the button’s events.Listing 5.1Subscribing to three of a button's eventsstatic void LogPlainEvent(object sender, EventArgs e){Console.WriteLine ("LogPlain");}static void LogKeyEvent(object sender, KeyPressEventArgs e){Console.WriteLine ("LogKey");}static void LogMouseEvent(object sender, MouseEventArgs e){Console.WriteLine ("LogMouse");}...Button button = new Button();button.Text = "Click me";button.Click += new EventHandler(LogPlainEvent);button.KeyPress += new KeyPressEventHandler(LogKeyEvent);button.MouseClick += new MouseEventHandler(LogMouseEvent);Form form = new Form();form.AutoSize=true;form.Controls.Add(button);Application.Run(form);The output lines in the three event handling methods are there to prove that the codeis working: if you press the spacebar with the button highlighted, you’ll see that theClick and KeyPress events are both raised; pressing Enter just raises the Click event;clicking on the button raises the Click and MouseClick events. In the following sectionswe’ll improve this code using some of the C# 2 features.Let’s start by asking the compiler to make a pretty obvious deduction—which delegatetype we want to use when subscribing to an event.Licensed to Rhona Hadida