Facade Pattern-优快云博客

举一个生活中的小例子，大凡开过学或者毕过业的都会体会到这样一种郁闷：你要去 n

个地方办理 n 个手续（现在大学合并后就更加麻烦，因为可能那 n 个地方都隔的比较远）。

但是实际上我们需要的就是一个最后一道手续的证明而已，对于前面的手续是怎么办的、到

什么地方去办理我们都不感兴趣。

实际上在软件系统开发中也经常回会遇到这样的情况，可能你实现了一些接口（模块），

而这些接口（模块）都分布在几个类中（比如 A和 B、C、D）：A中实现了一些接口，B 中

实现一些接口（或者 A代表一个独立模块，B、C、D代表另一些独立模块）。然后你的客户

程序员（使用你设计的开发人员）只有很少的要知道你的不同接口到底是在那个类中实现的，

绝大多数只是想简单的组合你的 A－D的类的接口，他并不想知道这些接口在哪里实现的。

This real-world code demonstrates the Facade pattern as a MortgageApplication object which provides a simplified interface to a large subsystem of classes measuring the creditworthyness of an applicant.

participants

The classes and/or objects participating in this pattern are:

Facade (MortgageApplication)
- knows which subsystem classes are responsible for a request.
- delegates client requests to appropriate subsystem objects.
Subsystem classes (Bank, Credit, Loan)
- implement subsystem functionality.
- handle work assigned by the Facade object.
- have no knowledge of the facade and keep no reference to it.

// Facade pattern -- Real World example

using System;

namespace DoFactory.GangOfFour.Facade.RealWorld
{
  // MainApp test application

  class MainApp
  {
    static void Main ()
    {
      // Facade
      Mortgage mortgage = new Mortgage();

      // Evaluate mortgage eligibility for customer
      Customer customer = new Customer("Ann McKinsey");
      bool eligable = mortgage.IsEligible(customer,125000);

      Console.WriteLine("/n" + customer.Name +
          " has been " + (eligable ? "Approved" : "Rejected"));

      // Wait for user
      Console.Read();
    }
  }

  // "Subsystem ClassA"

  class Bank
  {
    public bool HasSufficientSavings(Customer c, int amount)
    {
      Console.WriteLine("Check bank for " + c.Name);
      return true;
    }
  }

  // "Subsystem ClassB"

  class Credit
  {
    public bool HasGoodCredit(Customer c)
    {
      Console.WriteLine("Check credit for " + c.Name);
      return true;
    }
  }

  // "Subsystem ClassC"

  class Loan
  {
    public bool HasNoBadLoans(Customer c)
    {
      Console.WriteLine("Check loans for " + c.Name);
      return true;
    }
  }

  class Customer
  {
    private string name;

    // Constructor
    public Customer(string name)
    {
      this.name = name;
    }

    // Property
    public string Name
    {
      get{ return name; }
    }
  }

  // "Facade"

  class Mortgage
  {
    private Bank bank = new Bank();
    private Loan loan = new Loan();
    private Credit credit = new Credit();

    public bool IsEligible(Customer cust, int amount)
    {
      Console.WriteLine("{0} applies for {1:C} loan/n",
        cust.Name, amount);

      bool eligible = true;

      // Check creditworthyness of applicant
      if (!bank.HasSufficientSavings(cust, amount))
      {
        eligible = false;
      }
      else if (!loan.HasNoBadLoans(cust))
      {
        eligible = false;
      }
      else if (!credit.HasGoodCredit(cust))
      {
        eligible = false;
      }

      return eligible;
    }
  }
}

Output

Ann McKinsey applies for $125,000.00 loan

Check bank for Ann McKinsey
Check loans for Ann McKinsey
Check credit for Ann McKinsey

Ann McKinsey has been Approved