在職教師教育網路應用系統程式分享與實作研習 ---C# Tutorial(Code C)

1. 在職教師教育網路應用系統程式分享與實作研習---C# Tutorial(Code C) 行政網路組 傅志雄

2. Object Oriented Programming with C#

3. Classes and Objects • 抽象化(Abstraction)關念 • Defining Classes [attributes] [access-modifiers] class identifier [:base-class] {class-body} • [assembly:AssemblyKeyFile(".\\keyFile.snk")] public class Tester { public static Main( ) { //... } }

4. Classes and Objects-2 Simple Time class using System; public class Time { // public methods public void DisplayCurrentTime( ) { Console.WriteLine(“列印……"); } // private variables int Year; int Month; int Date; } public class Tester { static void Main( ) { Time t = new Time( ); t.DisplayCurrentTime( ); } }

5. Classes and Objects • Access Modifiers public private protected Internal(assembly) Protected internal

6. Encapsulation and Member Accessibility • Encapsulation--物件導向概念中，「封裝」可說是物件狀態的隱藏過程，或指程式實作的隱藏 (implementation hiding) • There are five levels of member accessibility • public: accessible to everyone • internal: accessible from within current assembly • private: accessible from this class only • protected: accessible from this class and from child classes • protected internal: union of protected and internal accessibility publicclass Customer { publicint Field1; internalint Field2; privateint Field3; protectedint Field4; protectedinternalint Field5; }

7. Classes and Objects-5 • Creating Objects Time t = new Time( );

8. Classes and Objects-4 • Method Arguments void MyMethod (int firstParam, string secondParam) { // ... }

9. Constructors • Constructors are special methods designed to initialize fields • CLR executes constructor whenever New is called on a class • creatable classes must have at least one constructor • constructors defined using procedures with same name as class name • constructors can be parameterized and overloaded • parameters passed by client after class name publicclass Customer { privatestring m_Name; privatestring m_Phone; public Customer(string Name, string Phone) { m_Name = Name; m_Phone = Phone; } } Customer c1; c1 = New Customer("Wendy", "432-4636"); Customer c2 =New Customer("Bob", "555-1212");

10. Default constructor • Non-parameterized constructor called "default constructor" • allows client to create object without passing parameters • C# compiler automatically adds a default constructor to classes that have no explicit constructor • default constructor (if desired) must be explicitly added to classes that contain other constructors publicclass Class1{ //no explicit constructor } publicclass Class3{ publicClass3(string s){ //implementation } publicClass3(){ //implementation } } publicclass Class2{ publicClass2(string s){ //implementation } } Class1 c1 = new Class1(); Class2 c2 = new Class2(); Class3 c3 = new Class3(); Calls default constructor Illegal: no default constructor Calls default constructor

11. Classes and Objects[Constructors] public class Time { public void DisplayCurrentTime( ) { System.Console.WriteLine("{0}/{1}/{2} {3}:{4}:{5}",Month, Date, Year, Hour, Minute, Second); } public Time(System.DateTime dt) { Year = dt.Year; Month = dt.Month; Date = dt.Day; Hour = dt.Hour; Minute = dt.Minute; Second = dt.Second; } int Year; int Month; int Date; int Hour; int Minute; int Second; } public class Tester { static void Main( ) { System.DateTime currentTime = System.DateTime.Now; Time t = new Time(currentTime); t.DisplayCurrentTime( ); } } //-------參考demo01.txt

12. Overloading methods and properties • Two or more class members can be given the same name • you can overload a set of methods or a set of properties • Overloaded members must differ with their parameter lists • parameter lists must differ in size and/or in sequence of types • you cannot overload based on return type or parameter name publicclass CustomerManager { publicstring GetCustomerInfo(int ID) { //implementation } public string GetCustomerInfo(string Name) { //implementation } } //client-side code string info1, info2; CustomerManager mgr = new CustomerManager(); //call GetCustomerInfo(Integer) info1 = mgr.GetCustomerInfo(23); //call GetCustomerInfo(String) info2 = mgr.GetCustomerInfo(“fu"); //-------參考demo02.txt

13. Encapsulation using Properties • Properties require new syntax • each property must implement a Get block and/or a Set block publicclass Customer { //private field privatestring m_Name; //property controlled access to private field publicstring Name { //perform calculations if necessary get { return m_Name; } //perform validation here if necessary set { m_Name = value; } } } Get block Set block //client-side code string s; Customer obj = new Customer(); obj.Name = “fu"; // triggers Set block s = obj.Name; // triggers Get block //-------參考demo03.txt

14. Implementation inheritance • An OOP technique to reuse code across classes • derived class inherits implementation from base class • inheritance relationships create inheritance hierarchies • Inheritance establishes "IS A" relationship between classes「是一個」VS. “Has A” Human Manager "IS A" Human Programmer "IS A" Human Manager Programmer SeniorManager ManagerTrainee

15. Inheriting from a base class • Class can explicitly inherit from a base class • class defines base class using Inherits keyword • class can only have one base class (no multiple inheritance) • Class without explicit base class inherits from System.Object publicclass Human{ publicstring Name; publicstring Speak() { return "Hi I am a human named:" + Name; } } publicclass Manager : Human { //Manager specific implementation here } publicclass Programmer : Human { //Programmer specific implementation here } //-------參考demo04.txt

16. Extending from a base class public class Human { public string Name; public string Speak() { return "Hi I am a human named:" + Name; } } public class Manager : Human { //Manager specific implementation here public string Name2; public string Speak2() { return "My Dad is"+Name+"---Hi I am a human named:" + Name2; } //-------參考demo05.txt

17. Base classes and constructors • Constructors and base types have "issues" • derived class contract doesn't include base class constructors • derived class must provide its own constructor(s) • derived class constructor must call a base class constructor • compiler can automatically generate call to accessible default constructor in base class constructor if one exists publicclass Human { protectedstring m_Name; public Human(string Name) { //implicit call to System.Object constructor m_Name = Name; } } publicclass Programmer : Human { //doesn't compile //base class has no accessible default constructor! } 編譯出問題

18. Constructor Chaining public class a { public a() { System.Console.WriteLine("產生a Class"); } } public class b : a { public b() { System.Console.WriteLine("產生b Class"); } } public class c : b { public c() { System.Console.WriteLine("產生c Class"); } } public class d : c { public d() { System.Console.WriteLine("產生d Class"); } } //-------參考demo06.txt

19. Calling base class constructor解決1 • Base class constructor called via base keyword • can only be called once publicclass Human {public Human() { } protectedstring m_Name; public Human(string Name) { //implicit call to System.Object constructor m_Name = Name; } } publicclass Programmer : Human { } 增加 空default Constructor //-------參考demo07.txt

20. Calling base class constructor解決2 • Base class constructor called via base keyword • can only be called once publicclass Human { protectedstring m_Name; public Human(string Name) { //implicit call to System.Object constructor m_Name = Name; } } publicclass Programmer : Human { public Programmer(string Name):base(Name) { //chaining a call to base class constructor } } Special syntax for constructors //-------參考demo08.txt

21. 11/21 止 • 待續………