ASP.NET PDF Viewer using C#, VB/NET

Because consumers of enumerations are free to stop enumerating at any time, in practice this sort of enumeration will just keep going until the calling code decides to stop. We ll see some slightly more practical uses for this when we explore parallel execution and multithreading later in the book. The concept of chaining lazy enumerations together shown in Example 7-35 is a very useful technique it s the basis of the most powerful feature that was added in version 3 of C#: LINQ. LINQ is such an important topic that the next chapter is devoted to it. But before we move on, let s review what we ve seen so far.

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Summary

this.getYear = function() { return m_Year; } this.dispose = function() { alert('bye ' + this.getName()); } } Type.registerClass('AtlasBook.Car', null, Web.IDisposable); In this code, first the namespace is registered as AtlasBook using the Type.registerNamespace command. Next, the class is implemented using a JavaScript function. Properties of the class are implemented using var declarations, and methods of the class using functions within the master function are assigned to the this object. So to implement a getModel method, you would simply use the following: this.getModel = function() { // Add Implementation here } Finally, the class is registered to the namespace using the Type.registerClass command. This takes three parameters, the first being the fully qualified name of the class, the second being the base type of the class (so if it inherits from another type, you would specify that here), and the last being the base interface of the class. You will learn more about inheritance and interfaces in the next sections. In this case, the base class is null, as Type doesn t inherit from any base class, and the interface is Web.IDisposable, which is an interface defined in Atlas.js that defines that the class will call the dispose method (if implemented) when it is being destroyed. Now, any JavaScript that includes this page will be able to create an instance of an AtlasBook.Car object by using the following script: var testCar = new AtlasBook.Car('Honda', 'Pilot', '2005'); Your code can then invoke methods on this object in the usual manner: Alert(testCar.getYear());

The .NET Framework s type system has intrinsic support for collections of items in the form of arrays. You can make arrays out of any type. They can be either simple singledimensional lists, nested arrays of arrays, or multidimensional rectangular arrays. The size of an array is fixed at the moment you create it, so when we need a bit more flexibility we use the List<T> generic collection class instead. This works more or less like an array, except we can add and remove items at will. (It uses arrays internally, dynamically allocating new arrays and copying elements across as necessary.) Both arrays and lists offer various services for finding and sorting elements. Thanks to the IEnumerable<T> interface, it s possible to write polymorphic code that can work with any kind of collection. And as we re about to see, LINQ takes that idea to a whole new level.

efficient choice, so the automatic setting always works, but you gain performance if you specify the connection to be queued.

LINQ, short for Language Integrated Query, provides a powerful set of mechanisms for working with collections of information, along with a convenient syntax. You can use LINQ with the arrays and lists we saw in the previous chapter anything that implements IEnumerable<T> can be used with LINQ, and there are LINQ providers for databases and XML documents. And even if you have to deal with data that doesn t fit into any of these categories, LINQ is extensible, so in principle, a provider could be written for more or less any information source that can be accessed from .NET. This chapter will focus mainly on LINQ to Objects the provider for running queries against objects and collections but the techniques shown here are applicable to other LINQ sources. Collections of data are ubiquitous, so LINQ can have a profound effect on how you program. Both of your authors have found that LINQ has changed how we write C# in ways we did not anticipate. Pre-LINQ versions of C# now feel like a different and significantly less powerful language. It may take a little while to get your head around how to use LINQ, but it s absolutely worth the effort. LINQ is not a single language feature it s the culmination of several elements that were added to version 3.0 of the C# language and version 3.5 of the .NET Framework. (Despite the different version numbers, these did in fact ship at the same time they were both part of the Visual Studio 2008 release.) So as well as exploring the most visible aspect of LINQ the query syntax we ll also examine the other associated language and framework features that contribute to LINQ.