外观模式设计系列教程

1、第 页外观模式设计系列教程3.2 外观模式的代码实现/ 子系统中的一个类 /public class SubSystemOne public void MethodeOne() Console.WriteLine(Sub System first method.); / 子系统中一个类 /public class SubSystemTwo public void MethodTwo() Console.WriteLine(Sub System second method.); / 子系统中一个类 /public class SubSystemThree public void MethodTh

2、ree() Console.WriteLine(Sub System third method.); / 子系统中一个类 /public class SubSystemFour public void MethodFour() Console.WriteLine(Sub System fourth method.); / 外观类 /public class Facade private SubSystemOne one; private SubSystemTwo two; private SubSystemThree three; private SubSystemFour four; pub

3、lic Facade() one = new SubSystemOne(); two = new SubSystemTwo(); three = new SubSystemThree(); four = new SubSystemFour(); public void MethodA() Console.WriteLine(nMethod group A); one.MethodeOne(); two.MethodTwo(); four.MethodFour(); public void MethodB() Console.WriteLine(nMethod group B); two.Met

4、hodTwo(); three.MethodThree(); 3.3 客户端代码class Program static void Main(string args) / 由于Facade的作用，客户端可以根本不知道子系统类的存在 Facade facade = new Facade(); facade.MethodA(); facade.MethodB(); Console.Read(); 运行结果4. 模式总结4.1 优点4.1.1 Facade模式降低了客户端对子系统运用的繁复性。4.1.2 外观模式松散了客户端与子系统的耦合关系，让子系统内部的模块能更简单扩展和维护。4.1.3 通过合

5、理运用Facade，可以援助我们更好的划分访问的层次。4.2 缺点过多的或者是不太合理的Facade也简单让人迷惑，究竟是调用Facade好呢，还是径直调用模块好。4.3 适用场景4.3.1 需要将设计进行分层时考虑Facade模式。4.3.2 在开发阶段，子系统往往由于重构变得越来越繁复，增加外观模式可以提供一个简约的接口，减削它们之间的依靠。4.3.3 在维护一个遗留的大型系统时，可以这个系统已经特别难以维护和扩展，可以为新系统开发一个Facade类，来提供设计粗糙或高度繁复的遗留代码的比较清楚简约的接口，让新系统与Facade对象交互，Facade与遗留代码交互全部繁复的工作。5. 应用

6、举例：分层开发中，对数据访问层我们增加DataAccess作为对外的接口来操作数据库子系统。5.1 实现类图5.2 实现代码public class Employee public string Name get; set; public int Age get; set; public Salary Salary get; set; public class Salary public DateTime From get; set; public DateTime To get; set; public decimal Amount get; set; public class Employ

7、eeDataAccess public void SaveEmployee(Employee employee) Console.WriteLine(Save employee to database.); public void DeleteEmployee(Employee employee) Console.WriteLine(Remode employee from database.); public class SalaryDataAccess public void SaveSalary(Salary salary) Console.WriteLine(Save salary t

8、o database.); public void DeleteSalary(Salary salary) Console.WriteLine(Remove salary from database.); / DataAccess为客户端提供一个简约的接口 /public class DataAccess private EmployeeDataAccess employeeDataAccess = new EmployeeDataAccess(); private SalaryDataAccess salaryDataAccess = new SalaryDataAccess(); publ

9、ic void SaveEmployee(Employee employee) / 先保存员工基本信息 employeeDataAccess.SaveEmployee(employee); / 保存员工薪水信息 salaryDataAccess.SaveSalary(employee.Salary); public void RemoveEmployee(Employee employee) / 先删除员工薪水信息 salaryDataAccess.DeleteSalary(employee.Salary); / 删除员工基本信息 employeeDataAccess.DeleteEmployee(employee); 5.3 客户端代码class Program static void Main(string args) DataAccess.DataAccess dataAccess = new DataAccess.DataAccess(); DataAccess.Employee employee = new DataAccess.Employee() Salary = new DataAccess.Salary(), Na