C Language Enhancements

Dynamic type Regardless of the value that myDynamicVar actually contains, this code will compile  If the requested member does not exist, you will get an exception when this code is e

C# Language Enhancements

Ebook: Beginning Visual C# 2010, part 1, chapter 14

Reference: Vietnamese Video

 Object initializers

 var type

Object Initializers

public class Student

{

private string id, name, add;

public Student()

{

}

public Student(string id, string name, string add)

{

this.id = id;

this.name = name;

this.add = add;

}

public string StudentID

{

get { return id; }

set { id = value; }

}

public string StudentName

{

get { return name; }

set { name = value; }

}

public string StudentAdd

{

get { return add; }

set { add = value; }

}

}

Slide 3

Student st1 = new Student("9912578", "Nguyen Van An",

"DN");

Student st2 = new Student();

st2.StudentID = "9912578";

st2.StudentName = "Nguyen Van An";

st2.StudentAdd = "DN";

Student st3 = new Student {

StudentID = "9912578", StudentName = "Nguyen Van An", StudentAdd = "DN"

};

var type

 C# allow to declare a variable with var keyword

 You can’t declare a variable using var without initializing the variable at the same time

 Example:

var i = 10;

var st = new Student();

var myArray = new[] { 4, 5, 2 };

var <varName> = <value>;

Anonymous types

encapsulate a set of read-only properties into a single

object without having to explicitly define a type first

var p = new {ID = "123456", Name = "Join"};

 An anonymous type cannot be: a field, a property, an

event, a formal parameter of a method or the return type

of a method

only if all their properties are equal

Slide 5

Dynamic type

 Regardless of the value that myDynamicVar actually contains, this code will compile

 If the requested member does not exist, you will get an

exception when this code is executed

 Example:

private dynamic TrungBinh(dynamic s1, dynamic s2)

{

return (s1 + s2) / 2;

}

private void button1_Click(object sender, EventArgs e)

{

dynamic tb = TrungBinh(2, 4);

lblOutput.Text = Convert.ToString( tb);

}

dynamic myDynamicVar;

Named and optional method

parameters

 Allow to define the parameter as optional in the method

definition by providing a default value that will be used if

none is supplied

 Default values must be either literal values, constant values, new object instances, or default value type values

 When you use optional values, they must appear at the end

of the list of parameters for a method

Slide 7

Named and optional method

parameters

 C# 4 introduces named parameters that enable you to

specify whichever parameters you want

 This doesn’t require you to do anything in particular in your method definition; it is a technique that you use when you are calling a method

 Example:

Student st = new Student(id: "9912578", name: "Nguyen Van An", address:

"Dong Nai");

MyMethod( <param1Name>: <param1Value>,

<paramNName>: <paramNValue>);

Extension methods

 Extension methods enable you to "add" methods to

existing types without creating a new derived type,

recompiling, or otherwise modifying the original type

 Syntax:

Slide 9

public static class ExtensionClass

{

public static <ReturnType><ExtensionMethodName>(

this <TypeToExtend> instance) {

} }

<TypeToExtend> myVar;

// myVar is initialized by code not shown here.

myVar.<ExtensionMethodName>();

Extension methods are defined as static methods but are called by using instance method syntax

Extension methods: Example

public static class myString

{

public static bool EqualsIgnoreCase( this string s1, string s2 )

{

return s1.Equals(s2, StringComparison.OrdinalIgnoreCase);

}

}

string s = "Join";

MessageBox.Show(s.EqualsIgnoreCase("join").ToString());