- •Contents at a Glance
- •Table of Contents
- •Acknowledgments
- •Introduction
- •Who This Book Is For
- •Finding Your Best Starting Point in This Book
- •System Requirements
- •Conventions and Features in This Book
- •Conventions
- •Other Features
- •Code Samples
- •Installing the Code Samples
- •Using the Code Samples
- •Support for This Book
- •Questions and Comments
- •Beginning Programming with the Visual Studio 2008 Environment
- •Writing Your First Program
- •Using Namespaces
- •Creating a Graphical Application
- •Chapter 1 Quick Reference
- •Understanding Statements
- •Identifying Keywords
- •Using Variables
- •Naming Variables
- •Declaring Variables
- •Working with Primitive Data Types
- •Displaying Primitive Data Type Values
- •Using Arithmetic Operators
- •Operators and Types
- •Examining Arithmetic Operators
- •Controlling Precedence
- •Using Associativity to Evaluate Expressions
- •Associativity and the Assignment Operator
- •Incrementing and Decrementing Variables
- •Declaring Implicitly Typed Local Variables
- •Chapter 2 Quick Reference
- •Declaring Methods
- •Specifying the Method Declaration Syntax
- •Writing return Statements
- •Calling Methods
- •Specifying the Method Call Syntax
- •Applying Scope
- •Overloading Methods
- •Writing Methods
- •Chapter 3 Quick Reference
- •Declaring Boolean Variables
- •Using Boolean Operators
- •Understanding Equality and Relational Operators
- •Understanding Conditional Logical Operators
- •Summarizing Operator Precedence and Associativity
- •Using if Statements to Make Decisions
- •Understanding if Statement Syntax
- •Using Blocks to Group Statements
- •Cascading if Statements
- •Using switch Statements
- •Understanding switch Statement Syntax
- •Following the switch Statement Rules
- •Chapter 4 Quick Reference
- •Using Compound Assignment Operators
- •Writing while Statements
- •Writing for Statements
- •Understanding for Statement Scope
- •Writing do Statements
- •Chapter 5 Quick Reference
- •Coping with Errors
- •Trying Code and Catching Exceptions
- •Handling an Exception
- •Using Multiple catch Handlers
- •Catching Multiple Exceptions
- •Using Checked and Unchecked Integer Arithmetic
- •Writing Checked Statements
- •Writing Checked Expressions
- •Throwing Exceptions
- •Chapter 6 Quick Reference
- •The Purpose of Encapsulation
- •Controlling Accessibility
- •Working with Constructors
- •Overloading Constructors
- •Understanding static Methods and Data
- •Creating a Shared Field
- •Creating a static Field by Using the const Keyword
- •Chapter 7 Quick Reference
- •Copying Value Type Variables and Classes
- •Understanding Null Values and Nullable Types
- •Using Nullable Types
- •Understanding the Properties of Nullable Types
- •Using ref and out Parameters
- •Creating ref Parameters
- •Creating out Parameters
- •How Computer Memory Is Organized
- •Using the Stack and the Heap
- •The System.Object Class
- •Boxing
- •Unboxing
- •Casting Data Safely
- •The is Operator
- •The as Operator
- •Chapter 8 Quick Reference
- •Declaring an Enumeration
- •Using an Enumeration
- •Choosing Enumeration Literal Values
- •Choosing an Enumeration’s Underlying Type
- •Working with Enumerations
- •Working with Structures
- •Declaring a Structure
- •Understanding Structure and Class Differences
- •Declaring Structure Variables
- •Understanding Structure Initialization
- •Copying Structure Variables
- •Chapter 9 Quick Reference
- •What Is an Array?
- •Declaring Array Variables
- •Creating an Array Instance
- •Initializing Array Variables
- •Creating an Implicitly Typed Array
- •Accessing an Individual Array Element
- •Iterating Through an Array
- •Copying Arrays
- •What Are Collection Classes?
- •The ArrayList Collection Class
- •The Queue Collection Class
- •The Stack Collection Class
- •The Hashtable Collection Class
- •The SortedList Collection Class
- •Using Collection Initializers
- •Comparing Arrays and Collections
- •Using Collection Classes to Play Cards
- •Chapter 10 Quick Reference
- •Using Array Arguments
- •Declaring a params Array
- •Using params object[ ]
- •Using a params Array
- •Chapter 11 Quick Reference
- •What Is Inheritance?
- •Using Inheritance
- •Base Classes and Derived Classes
- •Calling Base Class Constructors
- •Assigning Classes
- •Declaring new Methods
- •Declaring Virtual Methods
- •Declaring override Methods
- •Understanding protected Access
- •Understanding Extension Methods
- •Chapter 12 Quick Reference
- •Understanding Interfaces
- •Interface Syntax
- •Interface Restrictions
- •Implementing an Interface
- •Referencing a Class Through Its Interface
- •Working with Multiple Interfaces
- •Abstract Classes
- •Abstract Methods
- •Sealed Classes
- •Sealed Methods
- •Implementing an Extensible Framework
- •Summarizing Keyword Combinations
- •Chapter 13 Quick Reference
- •The Life and Times of an Object
- •Writing Destructors
- •Why Use the Garbage Collector?
- •How Does the Garbage Collector Work?
- •Recommendations
- •Resource Management
- •Disposal Methods
- •Exception-Safe Disposal
- •The using Statement
- •Calling the Dispose Method from a Destructor
- •Making Code Exception-Safe
- •Chapter 14 Quick Reference
- •Implementing Encapsulation by Using Methods
- •What Are Properties?
- •Using Properties
- •Read-Only Properties
- •Write-Only Properties
- •Property Accessibility
- •Understanding the Property Restrictions
- •Declaring Interface Properties
- •Using Properties in a Windows Application
- •Generating Automatic Properties
- •Initializing Objects by Using Properties
- •Chapter 15 Quick Reference
- •What Is an Indexer?
- •An Example That Doesn’t Use Indexers
- •The Same Example Using Indexers
- •Understanding Indexer Accessors
- •Comparing Indexers and Arrays
- •Indexers in Interfaces
- •Using Indexers in a Windows Application
- •Chapter 16 Quick Reference
- •Declaring and Using Delegates
- •The Automated Factory Scenario
- •Implementing the Factory Without Using Delegates
- •Implementing the Factory by Using a Delegate
- •Using Delegates
- •Lambda Expressions and Delegates
- •Creating a Method Adapter
- •Using a Lambda Expression as an Adapter
- •The Form of Lambda Expressions
- •Declaring an Event
- •Subscribing to an Event
- •Unsubscribing from an Event
- •Raising an Event
- •Understanding WPF User Interface Events
- •Using Events
- •Chapter 17 Quick Reference
- •The Problem with objects
- •The Generics Solution
- •Generics vs. Generalized Classes
- •Generics and Constraints
- •Creating a Generic Class
- •The Theory of Binary Trees
- •Building a Binary Tree Class by Using Generics
- •Creating a Generic Method
- •Chapter 18 Quick Reference
- •Enumerating the Elements in a Collection
- •Manually Implementing an Enumerator
- •Implementing the IEnumerable Interface
- •Implementing an Enumerator by Using an Iterator
- •A Simple Iterator
- •Chapter 19 Quick Reference
- •What Is Language Integrated Query (LINQ)?
- •Using LINQ in a C# Application
- •Selecting Data
- •Filtering Data
- •Ordering, Grouping, and Aggregating Data
- •Joining Data
- •Using Query Operators
- •Querying Data in Tree<TItem> Objects
- •LINQ and Deferred Evaluation
- •Chapter 20 Quick Reference
- •Understanding Operators
- •Operator Constraints
- •Overloaded Operators
- •Creating Symmetric Operators
- •Understanding Compound Assignment
- •Declaring Increment and Decrement Operators
- •Implementing an Operator
- •Understanding Conversion Operators
- •Providing Built-In Conversions
- •Creating Symmetric Operators, Revisited
- •Adding an Implicit Conversion Operator
- •Chapter 21 Quick Reference
- •Creating a WPF Application
- •Creating a Windows Presentation Foundation Application
- •Adding Controls to the Form
- •Using WPF Controls
- •Changing Properties Dynamically
- •Handling Events in a WPF Form
- •Processing Events in Windows Forms
- •Chapter 22 Quick Reference
- •Menu Guidelines and Style
- •Menus and Menu Events
- •Creating a Menu
- •Handling Menu Events
- •Shortcut Menus
- •Creating Shortcut Menus
- •Windows Common Dialog Boxes
- •Using the SaveFileDialog Class
- •Chapter 23 Quick Reference
- •Validating Data
- •Strategies for Validating User Input
- •An Example—Customer Information Maintenance
- •Performing Validation by Using Data Binding
- •Changing the Point at Which Validation Occurs
- •Chapter 24 Quick Reference
- •Querying a Database by Using ADO.NET
- •The Northwind Database
- •Creating the Database
- •Using ADO.NET to Query Order Information
- •Querying a Database by Using DLINQ
- •Creating and Running a DLINQ Query
- •Deferred and Immediate Fetching
- •Joining Tables and Creating Relationships
- •Deferred and Immediate Fetching Revisited
- •Using DLINQ to Query Order Information
- •Chapter 25 Quick Reference
- •Using Data Binding with DLINQ
- •Using DLINQ to Modify Data
- •Updating Existing Data
- •Adding and Deleting Data
- •Chapter 26 Quick Reference
- •Understanding the Internet as an Infrastructure
- •Understanding Web Server Requests and Responses
- •Managing State
- •Understanding ASP.NET
- •Creating Web Applications with ASP.NET
- •Building an ASP.NET Application
- •Understanding Server Controls
- •Creating and Using a Theme
- •Chapter 27 Quick Reference
- •Comparing Server and Client Validations
- •Validating Data at the Web Server
- •Validating Data in the Web Browser
- •Implementing Client Validation
- •Chapter 28 Quick Reference
- •Managing Security
- •Understanding Forms-Based Security
- •Implementing Forms-Based Security
- •Querying and Displaying Data
- •Understanding the Web Forms GridView Control
- •Displaying Customer and Order History Information
- •Paging Data
- •Editing Data
- •Updating Rows Through a GridView Control
- •Navigating Between Forms
- •Chapter 29 Quick Reference
- •What Is a Web Service?
- •The Role of SOAP
- •What Is the Web Services Description Language?
- •Nonfunctional Requirements of Web Services
- •The Role of Windows Communication Foundation
- •Building a Web Service
- •Creating the ProductsService Web Service
- •Web Services, Clients, and Proxies
- •Talking SOAP: The Easy Way
- •Consuming the ProductsService Web Service
- •Chapter 30 Quick Reference
368Part III Creating Components
5.Display the Program.cs file for the EnumeratorTest project in the Code and Text Editor window. Review the Main method in the Program.cs file. Recall from testing the earlier enumerator that this method instantiates a Tree<int> object, fills it with some data, and then uses a foreach statement to display its contents.
6.Build the solution, correcting any errors if necessary.
7.On the Debug menu, click Start Without Debugging.
The program runs and displays the values in the same sequence as before:
–12, –8, 0, 5, 5, 10, 10, 11, 14, 15
8.Press Enter and return to Visual Studio 2008.
If you want to continue to the next chapter
Keep Visual Studio 2008 running, and turn to Chapter 20. If you want to exit Visual Studio 2008 now
On the File menu, click Exit. If you see a Save dialog box, click Yes (if you are using Visual Studio 2008) or Save (if you are using Microsoft Visual C# 2008 Express Edition) and save the project.
Chapter 19 Quick Reference
To |
Do this |
Make a class enumerable,
allowing it to support the foreach construct
Implement the IEnumerable interface, and provide a GetEnumerator method that returns an IEnumerator object. For example:
public class Tree<TItem> : IEnumerable<TItem>
{
...
IEnumerator<TItem> GetEnumerator()
{
...
}
}
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Chapter 19 Enumerating Collections |
369 |
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Implement an enumerator |
Define an enumerator class that implements the IEnumerator |
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not by using an iterator |
interface and that provides the Current property and the MoveNext |
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method (and optionally the Reset method). For example: |
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public class TreeEnumerator<TItem> : IEnumerator<TItem> |
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{ |
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... |
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TItem Current |
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{ |
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get |
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{ |
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... |
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} |
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} |
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bool MoveNext() |
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{ |
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... |
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} |
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} |
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Define an enumerator by |
Implement the enumerator to indicate which items should be |
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using an iterator |
returned (using the yield statement) and in which order. For example: |
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IEnumerator<TItem> GetEnumerator()
{
for (...)
yield return ...
}
Chapter 20
Querying In-Memory Data by Using Query Expressions
After completing this chapter, you will be able to:
Define Language Integrated Query (LINQ) queries to examine the contents of enumerable collections.
Use LINQ extension methods and query operators.
Explain how LINQ defers evaluation of a query and how you can force immediate execution and cache the results of a LINQ query.
You have now met most of the features of the C# language. However, we have glossed over one important aspect of the language that is likely to be used by many applications—the support that C# provides for querying data. You have seen that you can define structures and classes for modeling data and that you can use collections and arrays for temporarily storing data in memory. However, how do you perform common tasks such as searching for items
in a collection that match a specific set of criteria? For example, if you have a collection of Customer objects, how do you find all customers that are located in London, or how can you
find out which town has the most customers for your services? You can write your own code to iterate through a collection and examine the fields in each object, but these types of tasks occur so often that the designers of C# decided to include features to minimize the amount of code you need to write. In this chapter, you will learn how to use these advanced C# language features to query and manipulate data.
What Is Language Integrated Query (LINQ)?
All but the most trivial of applications need to process data. Historically, most applications provided their own logic for performing these operations. However, this strategy can lead to the code in an application becoming very tightly coupled to the structure of the data that it processes; if the data structures change, you might need to make a significant number of changes to the code that handles the data. The designers of the Microsoft .NET Framework thought long and hard about these issues and decided to make the life of an application developer easier by providing features that abstract the mechanism that an application uses to
query data from application code itself. These features are called Language Integrated Query, or LINQ.
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