.NET/Java PDF, Tiff, Barcode SDK Library

You can add or remove references to suit whatever program you re building. To remove a reference, you can just select the library in the Solution Explorer and press the Delete key. (As it happens, our program is so simple that it depends only on the mandatory mscorlib library, so you could remove every DLL shown, and as long as you also remove any unused using directives from the source code, the program will still work.) To add a reference to a library, you can right-click on the References item and choose the Add Reference menu item. We ll explore all of this in more detail in 15. It s almost time to move on from Hello, world and start to explore more of the core language features, but first let s recap what we ve seen. The one line of executable code in our program invokes the WriteLine method of the System.Console class to print a message. This code lives inside a method whose special name, Main, marks it out as the method to run when the program starts. That method is contained by a class called Program, because C# requires all methods to belong to a type. This class is a member of the HelloWorld namespace, because we chose to follow the convention of having our namespace match the name of the compiled binary. Our program uses the using directives supplied by Visual Studio to be able to refer to the Console class without needing to specify its namespace explicitly. So if you take one more look at the program, you

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Gallio, external test runner is Icarus 285 Garret, Jesse James 167 GET 164 165, 235 236 GetControllerInstance 192, 196, 199, 201 GetRouteData 353 GetValueProvider 210 211 global constants 370 global content 306, 311 global data 268 Global.asax 193 194, 196, 198, 220 Google Suggest 380 Grid 66 69, 77 GridView 96, 99 100 guestbook 5, 10 GuestBookController 10, 14, 17, 19 GUID 229 Guid.TryParse 376 GuidComb() 331

now know what every single line is for. (It is reproduced in Example 2-3, with the unused using directives removed.)

using System; namespace HelloWorld { class Program { static void Main(string[] args) { Console.WriteLine("Hello, world"); } } }

With the whole example in one place, you can see clearly that the code is indented to reflect the structure. This is a common practice, but it s not strictly necessary. As far as the C# compiler is concerned, when it comes to the space between elements of the language, there s no difference between a single space, multiple spaces or tabs, or even blank lines the syntax treats any contiguous quantity of whitespace as it would a single space. So you are free to use space in your source code to improve legibility. This is why C# requires the use of braces to indicate containment, and it s also why there s a semicolon at the end of the line that prints out the message. Since C# doesn t care whether we have one statement of code per line, split the code across multiple lines, or cram multiple statements onto one line, we need to be explicit about the end of each instruction, marking it with a ; so that the compiler knows where each new step of the program begins.

F4 key 314 factored 56, 62 Feather, Michael 63 file input 69, 74 file system 193 filter 154, 284, 372, 376 379 context objects 376 FinalBuilder 80 Firebug 169 170 invaluable in AJAX development 178 Firefox 98, 113, 159 flexibility 127 flow 51 52, 55 fluent interface 67 Fluent NHibernate 328 FluentForm 294 295 FluentPage 299 folder 312 313 shared 45, 304 structure 228 form input 204 form posts 56 form values 54 55, 203, 210, 213 form, interacting with 293 FormatException 375 376 formatters 258, 260, 265 266 FormatValueCore 266 forms authentication 153 FormsAuthentication 134 FormsAuthentication.SignOut() 134 FormValueProviderFactory 210

4. 5.

One of the language features added to C# 3.0 for LINQ is support for extension methods. These are methods bolted onto a type by some other type. You can add new methods to an existing type, even if you can t change that type perhaps it s a type built into the .NET Framework. For example, the built-in string type is not something we get to change, and it s sealed, so we cannot derive from it either, but that doesn t stop us from adding new methods. Example 8-5 adds a new and not very useful Backwards method that returns a copy of the string with the characters in reverse order.*

* This is even less useful than it sounds. If the string in question contains characters that are required to be used in strict sequence, such as combining characters or surrogates, naively reversing the character order will have peculiar results. But the point here is to illustrate how to add new methods to an existing type, not to explain why it s surprisingly difficult to reverse a Unicode string.

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static class StringAdditions { // Naive implementation for illustrative purposes. // DO NOT USE in real code! public static string Backwards(this string input) { char[] characters = input.ToCharArray(); Array.Reverse(characters); return new string(characters); } }

Notice the this keyword in front of the first argument that indicates that Backwards is an extension method. Also notice that the class is marked as static you can only define extension methods in static classes. As long as this class is in a namespace that s in scope (either because of a using directive, or because it s in the same namespace as the code that wants to use it) you can call this method as though it were a normal member of the string class:

11

string stationName = "Finsbury Park"; Console.WriteLine(stationName.Backwards());