定义：用于为子系统中的接口提供统一的接口。

Facade设计模式定义了一个较高级的接口，它使得子系统的使用更加容易。

UML：

示例：

View Code 
  1 // Facade pattern -- Structural example 
  2 
  3 
  4 using System;
  5  
  6 
  7 namespace DoFactory.GangOfFour.Facade.Structural
  8  
  9 {
 10  
 11   /// <summary>
 12  
 13 /// MainApp startup class for Structural
 14  
 15 /// Facade Design Pattern.
 16  
 17 /// </summary>
 18  
 19   class MainApp
 20  
 21   {
 22  
 23     /// <summary>
 24  
 25 /// Entry point into console application.
 26  
 27 /// </summary>
 28  
 29     public static void Main()
 30  
 31     {
 32  
 33       Facade facade = new Facade();
 34  
 35 
 36       facade.MethodA();
 37  
 38       facade.MethodB();
 39  
 40  
 41       // Wait for user
 42  
 43       Console.ReadKey();
 44  
 45     }
 46  
 47   }
 48  
 49  
 50  
 51   /// <summary>
 52 
 53 /// The 'Subsystem ClassA' class
 54 
 55 /// </summary>
 56 
 57   class SubSystemOne
 58 
 59   {
 60  
 61     public void MethodOne()
 62  
 63     {
 64  
 65       Console.WriteLine(" SubSystemOne Method");
 66  
 67     }
 68  
 69   }
 70  
 71  
 72  
 73   /// <summary>
 74  
 75 /// The 'Subsystem ClassB' class
 76  
 77 /// </summary>
 78  
 79   class SubSystemTwo
 80  
 81   {
 82  
 83     public void MethodTwo()
 84  
 85     {
 86  
 87       Console.WriteLine(" SubSystemTwo Method");
 88  
 89     }
 90  
 91   }
 92  
 93  
 94  
 95   /// <summary>
 96  
 97 /// The 'Subsystem ClassC' class
 98  
 99 /// </summary>
100  
101   class SubSystemThree
102  
103   {
104  
105     public void MethodThree()
106  
107     {
108  
109       Console.WriteLine(" SubSystemThree Method");
110  
111     }
112  
113   }
114  
115  
116  
117   /// <summary>
118  
119 /// The 'Subsystem ClassD' class
120  
121 /// </summary>
122  
123   class SubSystemFour
124  
125   {
126  
127     public void MethodFour()
128  
129     {
130  
131       Console.WriteLine(" SubSystemFour Method");
132  
133     }
134  
135   }
136  
137  
138  
139   /// <summary>
140  
141 /// The 'Facade' class
142  
143 /// </summary>
144  
145   class Facade
146  
147   {
148  
149     private SubSystemOne _one;
150  
151     private SubSystemTwo _two;
152  
153     private SubSystemThree _three;
154  
155     private SubSystemFour _four;
156  
157  
158  
159     public Facade()
160  
161     {
162  
163       _one = new SubSystemOne();
164  
165       _two = new SubSystemTwo();
166  
167       _three = new SubSystemThree();
168  
169       _four = new SubSystemFour();
170  
171     }
172  
173  
174  
175     public void MethodA()
176  
177     {
178  
179       Console.WriteLine("\nMethodA() ---- ");
180  
181       _one.MethodOne();
182  
183       _two.MethodTwo();
184  
185       _four.MethodFour();
186  
187     }
188  
189  
190  
191     public void MethodB()
192  
193     {
194  
195       Console.WriteLine("\nMethodB() ---- ");
196  
197       _two.MethodTwo();
198  
199       _three.MethodThree();
200  
201     }
202  
203   }
204  
205 }
206

输出：

MethodA() ----

SubSystemOne Method

SubSystemTwo Method

SubSystemFour Method
MethodB() ----

SubSystemTwo Method

SubSystemThree Method

View Code 
  1 // Facade pattern -- Real World example 
  2 
  3 
  4 using System;
  5  
  6 
  7 namespace DoFactory.GangOfFour.Facade.RealWorld
  8 
  9 {
 10 
 11   /// <summary>
 12 
 13 /// MainApp startup class for Real-World 
 14 
 15 /// Facade Design Pattern.
 16 
 17 /// </summary>
 18 
 19   class MainApp
 20 
 21   {
 22 
 23     /// <summary>
 24 
 25 /// Entry point into console application.
 26 
 27 /// </summary>
 28 
 29     static void Main()
 30 
 31     {
 32 
 33       // Facade
 34 
 35       Mortgage mortgage = new Mortgage();
 36 
 37 
 38       // Evaluate mortgage eligibility for customer
 39 
 40       Customer customer = new Customer("Ann McKinsey");
 41 
 42       bool eligible = mortgage.IsEligible(customer, 125000);
 43 
 44 
 45       Console.WriteLine("\n" + customer.Name +
 46 
 47           " has been " + (eligible ? "Approved" : "Rejected"));
 48 
 49 
 50       // Wait for user
 51 
 52       Console.ReadKey();
 53 
 54     }
 55 
 56   }
 57 
 58 
 59 
 60   /// <summary>
 61 
 62 /// The 'Subsystem ClassA' class
 63 
 64 /// </summary>
 65 
 66   class Bank
 67 
 68   {
 69 
 70     public bool HasSufficientSavings(Customer c, int amount)
 71 
 72     {
 73 
 74       Console.WriteLine("Check bank for " + c.Name);
 75 
 76       return true;
 77 
 78     }
 79 
 80   }
 81 
 82 
 83   /// <summary>
 84 
 85 /// The 'Subsystem ClassB' class
 86 
 87 /// </summary>
 88 
 89   class Credit
 90 
 91   {
 92 
 93     public bool HasGoodCredit(Customer c)
 94 
 95     {
 96 
 97       Console.WriteLine("Check credit for " + c.Name);
 98 
 99       return true;
100 
101     }
102 
103   }
104 
105 
106   /// <summary>
107 
108 /// The 'Subsystem ClassC' class
109 
110 /// </summary>
111 
112   class Loan
113 
114   {
115 
116     public bool HasNoBadLoans(Customer c)
117 
118     {
119 
120       Console.WriteLine("Check loans for " + c.Name);
121 
122       return true;
123 
124     }
125 
126   }
127 
128 
129   /// <summary>
130 
131 /// Customer class
132 
133 /// </summary>
134 
135   class Customer
136 
137   {
138 
139     private string _name;
140 
141 
142     // Constructor
143 
144     public Customer(string name)
145 
146     {
147 
148       this._name = name;
149 
150     }
151 
152 
153 
154     // Gets the name
155 
156     public string Name
157 
158     {
159 
160       get { return _name; }
161 
162     }
163 
164   }
165 
166 
167 
168   /// <summary>
169 
170 /// The 'Facade' class
171 
172 /// </summary>
173 
174   class Mortgage
175 
176   {
177 
178     private Bank _bank = new Bank();
179 
180     private Loan _loan = new Loan();
181 
182     private Credit _credit = new Credit();
183 
184     public bool IsEligible(Customer cust, int amount)
185     {
186 
187       Console.WriteLine("{0} applies for {1:C} loan\n",
188 
189         cust.Name, amount);
190  
191       bool eligible = true;
192 
193 
194       // Check creditworthyness of applicant
195 
196       if (!_bank.HasSufficientSavings(cust, amount))
197 
198       {
199 
200         eligible = false;
201 
202       }
203 
204       else if (!_loan.HasNoBadLoans(cust))
205 
206       {
207 
208         eligible = false;
209 
210       }
211 
212       else if (!_credit.HasGoodCredit(cust))
213 
214       {
215 
216         eligible = false;
217 
218       }
219 
220       return eligible;
221 
222     }
223 
224   }
225  
226 }
227

输出：

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