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Introduction to Web Application

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Presentation on theme: "Introduction to Web Application"— Presentation transcript:

1 Introduction to Web Application
Advanced C#

2 Topics Common Type System Delegate Event C# 2.0

3 CTS Overview An Introduction to the Common Type System
Elements of the Common Type System Object-Oriented Characteristics

4 An Introduction to the Common Type System
Common Type System Architecture Value Types vs. Reference Types

5 Common Type System Architecture

6 Value Types vs. Reference Types
Value Types Are Primitive or User-Defined Structures Allocated on stack Assigned as copies Default behavior is pass by value Reference Types Are Objects That Are: Allocated on heap using the new keyword Assigned as references Passed by reference

7 Elements of the Common Type System
Primitive Types Objects Constructors Properties Custom Types Enumerations Interfaces

8 Primitive Types Simple Small Types Common in Most Languages
Naming Differences C# Support Conversions

9 Objects Every Class Inherits from System.Object
Objects Specify Data and Behavior Fields Define the Data Methods Define the Behavior class Accumulator { public float Result; public void Add(float amount) Result += amount; }

10 Constructors Constructors Are Used to Initialize Classes
Constructors Can Have Zero or More Parameters class Rectangle { private int x1,y1,x2,y2; public Rectangle(int x1, int y1, int x2,int y2) this.x1 = x1; this.x2 = x2; this.y1 = y1; this.y2 = y2; }

11 Properties Properties Are Similar to Fields
Properties Use get and set Accessor Methods for Managing Data Values public float Start { get return start; } set if (start >= 0) start = value;

12 Custom Types Inherit from System.ValueType
Are Defined with the struct Keyword in C# Can Have Methods, Properties, and Fields struct Employee { public string Name; public ushort Age; public DateTime HireDate; public float Tenure() TimeSpan ts = DateTime.Now – HireDate; return ts.Days/(float)365; }

13 Enumerations .NET Framework Enumerations Inherit from System.Enum
Use the enum keyword enum Color { Red, //0 Green, //1 Blue //2 } Color.Red;

14 Interfaces An Interface Is a Contractual Description of Methods and Properties An Interface Has No Implementation Use Casting in Client Code to Use an Interface interface ICDPlayer { void Play(short playTrackNum); void Pause(); void Skip(short numTracks); short CurrentTrack get; set; }

15 Object-Oriented Characteristics
Abstraction Encapsulation Inheritance Polymorphism

16 Abstraction Abstraction Works from the Specific to the General
Grouping Elements Makes It Easier to Work with Complex Data Types Abstraction Is Supported Through Classes

17 Encapsulation Encapsulation Is the Process of Hiding Internal Details of a Class Encapsulation Keywords public protected protected internal internal private Type-Level Accessibility Nested Classes

18 Inheritance Inheritance Is the Reuse of Class Members in Other Classes
The Common Type System Only Supports Single Inheritance for Classes Member Hiding Redefine the same method in the derived class Use the new keyword Abstract Members Sealed Classes

19 Polymorphism Polymorphism Allows a Reference Variable to Call the Correct Method Virtual Methods Enable Polymorphism in the Common Type System Use the virtual keyword in the base class Use the override keyword in the derived class Sealed Methods

20 A complex application public abstract class Expression{ public abstract double Evaluate(Hashtable vars); } Expression e = new Operation( new VariableReference("x"), '*', new Operation(new VariableReference("y"), '+', new Constant(2)));

21 public class Constant: Expression { double value;
public Constant(double value) { this.value = value; } public override double Evaluate(Hashtable vars) { return value; } }

22 public class VariableReference: Expression
{ string name; public VariableReference(string name) { = name; } public override double Evaluate(Hashtable vars) { object value = vars[name]; if (value == null) { throw new Exception("Unknown variable: " + name); } return Convert.ToDouble(value); } }

23 public class Operation: Expression
{ Expression left; char op; Expression right; public Operation(Expression left, char op, Expression right) { this.left = left; this.op = op; this.right = right; } public override double Evaluate(Hashtable vars) { double x = left.Evaluate(vars); double y = right.Evaluate(vars); switch (op) { case '+': return x + y; case '-': return x - y; case '*': return x * y; case '/': return x / y; } throw new Exception("Unknown operator");}}

24 Example Expression e = new Operation( new VariableReference("x"), '+', new Constant(3)); Hashtable vars = new Hashtable(); vars["x"] = 3; Console.WriteLine(e.Evaluate(vars));

25 e is a object of Operation, call Operation’s Evaluation
e.Evalution 3+3=6 e is a object of Operation, call Operation’s Evaluation left.Evaluate(vars); right.Evaluate(vars); left is a object of VariableReference right is a object of Contant 3 3 Find x’s value in vars return Contant

26 Overload static void F() { Console.WriteLine("F()"); }
static void F(object x) { Console.WriteLine("F(object)"); static void F(int x) { Console.WriteLine("F(int)"); static void F(double x) { Console.WriteLine("F(double)"); static void F(double x, double y) { Console.WriteLine("F(double, double)");

27 Delegate and Event Overview
Delegates Multicast Delegates Events When to Use Delegates, Events, and Interfaces

28 Java Programming import java.lang.reflect.*; public class HelloWorld {
catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (NoSuchMethodException e){ } catch (InstantiationException e){ } catch (IllegalAccessException e){ } catch (InvocationTargetException e){ } import java.lang.reflect.*; public class HelloWorld { public static void main(String[] args){ try { Class c = Class.forName("HelloWorld"); Method[] methodList = c.getDeclaredMethods(); for (int i=0; i<methodList.length; i++){ System.out.println(methodList[i].toString()); } Method m = c.getMethod("hello", null); Object o = c.newInstance(); m.invoke(o, null);}} public void hello(){ System.err.println("HelloWorld"); }}

29 Delegates Delegate Scenario Declaring a Delegate
Instantiating a Delegate Calling a Delegate

30 OnFlipCallback method
Delegate Scenario 1 - Change in switch position invokes switch’s OnFlip method OnFlip method Switch Object OnFlip method Switch Object OnFlipCallback method Light Object Delegate object 2 - OnFlip Method invokes delegate 3 - Delegate invokes light’s OnFlipCallback method 4 - OnFlipCallback method changes light’s state

31 Declaring a Delegate A Delegate Declaration Defines a Type That Encapsulates a Method with a Particular Set of Arguments and Return Type // declares a delegate for a method that takes a single // argument of type string and has a void return type delegate void MyDelegate1(string s);

32 Instantiating a Delegate
A Delegate Object Is Created with the new Operator Delegate Objects Are Immutable // instantiating a delegate to a static method Hello // in the class MyClass MyDelegate1 a = new MyDelegate1(MyClass.Hello); // instantiating a delegate to an instance method // AMethod in object p MyClass p = new MyClass(); MyDelegate1 b = new MyDelegate1(p.AMethod);

33 Calling a Delegate Use a Statement Containing:
The name of the delegate object Followed by the parenthesized arguments to be passed to the delegate // given the previous delegate declaration and // instantiation, the following invokes MyClass' // static method Hello with the parameter "World" a("World");

34 Multicast Delegates Multicast Delegate Scenario
Single vs. Multicast Delegates Creating and Invoking Multicast Delegates C# Language-Specific Syntax Delegate Details

35 Multicast Delegate Scenario
4 - OnFlipCallback method changes light1’s state 1 - Change in switch position invokes switch’s OnFlip method OnFlip method Switch Object OnFlip method Switch Object OnFlipCallback method Light1 Object OnFlipCallback method Light2 Object Multicast delegate1 object Multicast delegate2 object Invocation list 2 - OnFlip method invokes multicast delegate1 3 - delegate1 invokes light1’s OnFlipCallback 7 - OnFlipCallback method changes light2’s state 5 - delegate2 is invoked 6 - delegate2 invokes light2’s OnFlipCallback

36 Single vs. Multicast Delegates
All Delegates Have an Invocation List of Methods That Are Executed When Their Invoke Method is Called Single-Cast Delegates: Derived Directly From System.MulticastDelegate Invocation list contains only one method Multicast Delegates: Derived from System.MulticastDelegate Invocation list may contain multiple methods Multicast delegates contain two static methods to add and remove references from invocation list: Combine and Remove Use GetInvocationList to Obtain an Invocation List as an Array of Delegate References Use a Delegate’s Target and Method Properties to Determine: Which object will receive the callback Which method will be called

37 Creating and Invoking Multicast Delegates
// assign to c the composition of delegates a and b c = (MyDelegate2)Delegate.Combine(a, b); // assign to d the result of removing a from c d = (MyDelegate2)Delegate.Remove(c, a); // Iterate through c's invocation list // and invoke all delegates except a Delegate[] DelegateList = c.GetInvocationList(); for (int i = 0; i < DelegateList.Length; i++) { if (DelegateList[i].Target != aFoo1) { ((MyDelegate2) DelegateList[i])(); }

38 C# Language-Specific Syntax
C# Delegates That Return Void Are Multicast Delegates In C#, Use the + and - Operators to Add and Remove Invocation List Entries Less verbose than Combine and Remove methods MyDelegate a, b, c, d; a = new MyDelegate(Foo); b = new MyDelegate(Bar); c = a + b; // Compose two delegates to make another d = c - a; // Remove a from the composed delegate a += b; // Add delegate b to a's invocation list a -= b; // Remove delegate b from a's list

39 Demonstration: Delegates

40 code delegate void D(int x); D cd1 = new D(c.M1); D cd2 = new D(C.M2);
using System; namespace TestApp { delegate void D(int x); class Test static void Main() C c = new C(); D cd1 = new D(c.M1); D cd2 = new D(C.M2); D cd3 = cd1 + cd2 + cd2 + cd1;// M1 + M2 + M2 + M1 cd3(10); cd3 -= cd1; // => M1 + M2 + M2 cd3(20); cd3 = cd1 + cd2 + cd2 + cd1; // M1 + M2 + M2 + M1 cd3 -= cd1 + cd2; // => M2 + M1 cd3(30); cd3 -= cd2 + cd2; // => M1 + M1 cd3 -= cd2 + cd1; // => M1 + M2 cd3 -= cd1 + cd1; // => M1 + M2 + M2 + M1 }

41 class C { public void M1(int i) { Console.WriteLine("1 Hello "+i); } public static void M2(int i) { Console.WriteLine("2 Hello "+i); } }

42 Delegate Details A Delegate Declaration Causes the Compiler to Generate a New Class // delegate void MyDelegate3(string val); class MyDelegate3 : System.MulticastDelegate { public MyDelegate3(object obj, methodref mref) : base (obj, mref) { //... } public void virtual Invoke(string val) { //... };

43 Events Event Scenario Declaring an Event Connecting to an Event
Raising an Event

44 Event Scenario Mouse Object SoundMaker Object MouseClicked field
MouseClicked method MouseClicked method Invocation List: multicast delegate object multicast delegate object multicast delegate object multicast delegate object multicast delegate object stopButton object MouseClicked method MouseClicked method add_MouseClicked method add_MouseClicked method remove_MouseClicked method remove_MouseClicked method OnMouseClicked method OnMouseClicked method

45 Declaring an Event An event is a member that enables a class or object to provide notifications. An event is declared like a field except that the declaration includes an event keyword and the type must be a delegate type. // MouseClicked delegate declared public delegate void MouseClickedEventHandler(); public class Mouse { // MouseClicked event declared public static event MouseClickedEventHandler MouseClicked; //... }

46 Connecting to an Event Connect by Combining Delegates
Disconnect by Removing Delegates // Client’s method to handle the MouseClick event private void MouseClicked() { //... } //... // Client code to connect to MouseClicked event Mouse.MouseClicked += new MouseClickedEventHandler(MouseClicked); // Client code to break connection to MouseClick event Mouse.MouseClicked -= new

47 Raising an Event Check Whether Any Clients Have Connected to This Event If the event field is null, there are no clients Raise the Event by Invoking the Event’s Delegate if (MouseClicked != null) MouseClicked();

48 .NET Framework Guidelines
Name Events with a Verb and Use Pascal Casing Use “Raise” for Events, Instead of “Fire” Event Argument Classes Extend System.EventArgs Event Delegates Return Void and Have Two Arguments Use a Protected Virtual Method to Raise Each Event public class SwitchFlippedEventArgs : EventArgs { //... } public delegate void SwitchFlippedEventHandler( object sender, SwitchFlippedEventArgs e); public event SwitchFlippedEventHandler SwitchFlipped;

49 When to Use Delegates, Events, and Interfaces
Use a Delegate If: You basically want a C-style function pointer You want single callback invocation The callback should be registered in the call or at construction time, not through an add method call Use Events If: Client signs up for the callback function through an add method call More than one object will care You want end users to be able to easily add a listener to the notification in the visual designer Use an Interface If: The callback function entails complex behavior, such as multiple methods

50 C# 2.0 Overview Generics Iterators Partial Class …
Generic types are added to the language to enable programmers to achieve a high level of code reuse and enhanced performance for collection classes. Generic types can differ only by arity. Parameters can also be forced to be specific types. See Generic Type Parameters (C#) for more information. Iterators Iterators make it easier to dictate how a foreach loop will iterate over a collection's contents Partial Class Partial type definitions allow a single type, such as a class, to be split into multiple files. The Visual Studio designer uses this feature to separate its generated code from user code

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