写给自己看的小设计4 - 对象设计通用原则之扩展原则

1. 只与你的朋友说话
2. 不和陌生人说话
3. 对象应该只与必须交互的对象通信

(1) 当前对象本身(this)；
(2) 以参数形式传入到当前对象方法中的对象；
(3) 当前对象的成员对象；
(4) 如果当前对象的成员对象是一个集合，那么集合中的元素也都是可以交互的；
(5) 当前对象所创建的对象。

// 方法链式调用，此种方式在Web页面开发中倒是常用，但是静态语言中似乎不推荐
public void Do()
{
  m_accessor.GetUser().Rename();
}
// 无谓的公开方法
class UI
{
 public void Do()
 {
  WorkHelper();
 }
 
 public void WorkHelper() { }
}

public class Program
{
 static void Main(string[] args)
 {
  User user = new User();
  View ui = new View(user);
  user.Name = "Hello";
 }
}
 
delegate void OnNameChange(string name);
class View
{
 public View(User user)
 {
  user.onNameChanged += user_onNameChanged;
 }
 
 void user_onNameChanged(string name)
 {
  Console.WriteLine(name);
 }
}
 
class User
{
 private string m_name;
 public string Name
 {
  get { return m_name; }
  set
  {
   m_name = value;
   onNameChanged(m_name);
  }
 }
 public event OnNameChange onNameChanged;
}

class User
{
 public virtual void PrintType() { }
}
class Admin : User
{
 public override void PrintType() { Console.WriteLine("Employer"); }
}
class Programmer : User
{
 public override void PrintType() { Console.WriteLine("Employer"); }
}
class Manager : User
{
 public override void PrintType() { Console.WriteLine("Employer"); }
}
class Contractor : User
{
 public override void PrintType() { Console.WriteLine("Temp"); }
}

public class Program
{
 static void Main(string[] args)
 {
  User admin = new Admin(new EmployerPrintor());
  admin.PrintType();
  User contractor = new Contractor(new TempPrintor());
  contractor.PrintType();
 }
}
 
class User
{
 Printor m_printor;
 public User(Printor printor)
 {
  m_printor = printor;
 }
 
 public virtual void PrintType() { m_printor.PrintType(); }
}
class Admin : User
{
 public Admin(Printor printor)
  :base(printor)
 {
 
 }
}
class Contractor : User
{
 public Contractor(Printor printor)
  : base(printor)
 {
 
 }
}
 
class Printor
{
 public virtual void PrintType() { }
}
class EmployerPrintor : Printor
{
 public override void PrintType() { Console.WriteLine("Employer"); }
}
class TempPrintor : Printor
{
 public override void PrintType() { Console.WriteLine("Temp"); }
}