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Chapte r10 - Delegate, Events and Lambdas pdf
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Mô tả chi tiết
Chapter 10.
Delegates,Events, and Lambdas
Hoang Anh Viet
HaNoi University of Technology
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Objectives
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“The purpose of Chapter 10 is to demystify the delegate type.
Simply put, a .NET delegate is an object that “points” to other
methods in your application. Using this pattern, you are able to
build systems that allow multiple objects to engage in a two-way
onversation. After you have examined the use of .NET delegates,
you will then be introduced to the C# event keyword, which is
used to implify the manipulation of raw delegate programming.
You wrap up by investigating the role of the C# 2008 lambda
operator (=>) and exploring the connection between delegates,
anonymous methods, and lambda expressions.”
Microsoft Microsoft
Roadmap
10.1 Understanding the .NET Delegate Type
10.2 Defining a Delegate in C#
10.3 The System.MulticastDelegate and System.Delegate
Base class.
10.4 The Simplest Possible Delegate Example
10.5 Retrofiting the Car Type with Delegates
10.6 A more Elaborate Delegate Example
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Roadmap
10.7 Understanding Delegate Covarance
10.8 Greating Generic Delegates
10.9 Understanding C# Events.
10.10 The Generic C# EventHandler<T> Delegate.
10.11 Understanding C# Anonymouns Methods
10.12 Understanding Method Group Conversions
10.13 The C# 2008 Lambdas Operator.
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10.1 Understanding the .NET Delegate
Type
A delegate is a type that references a method.
Once a delegate is assigned a method, it behaves exactly
like that method .
The delegate method can be invoked like any other
method, with parameters and a return value.
Such as :
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public delegate int PerformCalculation(int x, int y);
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Kinds of Methods
Any method from any accessible class or struct that
matches the delegate's signature, which consists of the
return type and parameters, can be assigned to the
delegate .
The method can be either static or an instance method .
Note :
• In the context of method overloading:
The signature of a method does not include the
return value.
• In the context of delegates:
The signature does include the return value.
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Delegates Overview
Delegates have the following properties:
• Delegates are like C++ function pointers but are type
safe.
• Delegates allow methods to be passed as
parameters.
• Delegates can be used to define callback methods.
• Delegates can be chained together; for example,
multiple methods can be called on a single event.
• Methods do not have to match the delegate signature
exactly
• Allow code blocks to be passed as parameters in
place of a separately defined method.
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Efficency of Delegates
Plug new code into existing classes.
Makes it possible to programmatically change method
calls.
Defines callback methods. Allows for an algorithm to be
written in a more general way.
Microsoft Microsoft
Roadmap
10.1 Understanding the .NET Delegate Type
10.2 Defining a Delegate in C#
10.3 The System.MulticastDelegate and System.Delegate
Base class.
10.4 The Simplest Possible Delegate Example
10.5 Retrofiting the Car Type with Delegates
10.6 A more Elaborate Delegate Example
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