静态实现AOP(翻译自MSDN)

在.net实现AOP

本文通过一个简单的例子实现静态AOP.改例子主要实现客户的增删改查，突然有一天你的老板需要在程序上跟踪每个方法操作的运行日志。

主要分为5个步骤。

第一步：创建接口IRepository<T>，代码定义如下：

    public interface IRepository<T>
    {
      void Add(T entity);
      void Delete(T entity);
      void Update(T entity);
      IEnumerable<T> GetAll();
      T GetById(int id);
    }

第2步：创建Repository<T>类，实现代码IRepository<T>，代码如下：

    public class Repository<T> : IRepository<T>
    {
      public void Add(T entity)
      {
    Console.WriteLine("Adding {0}", entity);
      }
      public void Delete(T entity)
      {
    Console.WriteLine("Deleting {0}", entity);
      }
      public void Update(T entity)
      {
    Console.WriteLine("Updating {0}", entity);
      }
      public IEnumerable<T> GetAll()
      {
    Console.WriteLine("Getting entities");
    return null;
      }
      public T GetById(int id)
      {
    Console.WriteLine("Getting entity {0}", id);
    return default(T);
      }
    }

第3步，用Repository<T>实现Customer 的增删改查，Customer 定义如下：

    public class Customer
    {
      public int Id { get; set; }
      public string Name { get; set; }
      public string Address { get; set; }
    }

第4步，在控制台程序，运行，代码看起来如下：

    static void Main(string[] args)
    {
      Console.WriteLine("***\r\n Begin program - no logging\r\n");
      IRepository<Customer> customerRepository =new Repository<Customer>();
      var customer = new Customer
      {
        Id = 1,
        Name = "Customer 1",
        Address = "Address 1"
      };
      customerRepository.Add(customer);
      customerRepository.Update(customer);
      customerRepository.Delete(customer);
      Console.WriteLine("\r\nEnd program - no logging\r\n***");
      Console.ReadLine();
    }

按F5运行，运行结果如下图：

现在假如你的老板，需要在类中增加日志功能，你可以新建一个LoggerRepository<T>类，让他同样实现IRepository<T>，代码如下：

    public class LoggerRepository<T> : IRepository<T>
    {
      private readonly IRepository<T> _decorated;
      public LoggerRepository(IRepository<T> decorated)
      {
            _decorated = decorated;
      }
      private void Log(string msg, object arg = null)
      {
        Console.ForegroundColor = ConsoleColor.Red;
        Console.WriteLine(msg, arg);
        Console.ResetColor();
       }
      public void Add(T entity)
      {
        Log("In decorator - Before Adding {0}", entity);
        _decorated.Add(entity);
        Log("In decorator - After Adding {0}", entity);
      }
      public void Delete(T entity)
      {
        Log("In decorator - Before Deleting {0}", entity);
        _decorated.Delete(entity);
        Log("In decorator - After Deleting {0}", entity);
      }
      public void Update(T entity)
      {
        Log("In decorator - Before Updating {0}", entity);
        _decorated.Update(entity);
        Log("In decorator - After Updating {0}", entity);
      }
      public IEnumerable<T> GetAll()
      {
        Log("In decorator - Before Getting Entities");
        var result = _decorated.GetAll();
        Log("In decorator - After Getting Entities");
        return result;
      }
      public T GetById(int id)
      {
        Log("In decorator - Before Getting Entity {0}", id);
        var result = _decorated.GetById(id);
        Log("In decorator - After Getting Entity {0}", id);
        return result;
      }
    }

这个新类，已经包装了包装类，实现日志记录功能，现在需要做小的改动，代码实现如下：

static void Main(string[] args)
    {
      Console.WriteLine("***\r\n Begin program - logging with decorator\r\n");
      // IRepository<Customer> customerRepository =
      //   new Repository<Customer>();
      IRepository<Customer> customerRepository =
    new LoggerRepository<Customer>(new Repository<Customer>());
      var customer = new Customer
      {
        Id = 1,
        Name = "Customer 1",
        Address = "Address 1"
      };
      customerRepository.Add(customer);
      customerRepository.Update(customer);
      customerRepository.Delete(customer);
      Console.WriteLine("\r\nEnd program - logging with decorator\r\n***");
      Console.ReadLine();
    }

继续运行，运行结果如下：

到此为止，你可能会想:OK,这个想法是好的,但它仍然需要做很多工作:我必须实现所有的类和添加方面的所有方法。这将是难以维护。

有另一种方式去做吗？.net框架,您可以使用反射来得到所有方法和执行它们。基类库(BCL)甚至有RealProxy类(bit.ly/18MfxWo),为你实现。

答案：是的有的就是我们所讲的动态代理实现AOP; 我们将在下一节讲

AOP参考

本文翻译自：https://msdn.microsoft.com/en-us/magazine/dn574804.aspx（面向切面编程）

巴特西

静态实现AOP(翻译自MSDN)

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