理解适配器模式 [英] Understanding Adapter Pattern

问题描述

我正在尝试了解适配器模式及其在现实世界中的使用.在浏览了 Internet 和 www.dofactory.com 上的各种文章后，我创建了此示例代码.我只是想知道我的理解是否正确.在下面的示例中，我在 Adapter 类中创建了 MSDAO 对象.后来改成了OracleDAO.

I am trying to understand Adapter pattern and its use in real world. After going through various articles on internet and www.dofactory.com, I created this sample code. I just want to know whether my understanding is correct. In the example below I have created MSDAO object in the Adaptor class. Later I changed it to OracleDAO.

class Client
{
  static void Main(string[] args)
  {
    ITarget objAdapter = new Adapter();
    object dummyObject = objAdapter.GetData();
  }
}

Interface ITarget
{
  public void GetData();
}

//Decision to use MSDAO

class Adapter : ITarget
{
  public void GetData()
  {
    MSDAO objmsdao = new MSDAO();
    objmsdao.GetData();
  }
}

//After a month, the decision to use OracaleDAO was taken, so the code change

class Adapter : ITarget
{
  public void GetData()
  {
    OracleDAO objoracledao = new OracleDAO();
    objoracledao.GetData();
  }
}

推荐答案

通常，适配器模式将一个接口转换为另一个接口，但它可以简单地包装行为以将您的类与底层实现隔离.在您的情况下，您使用的是适配器，但您可以轻松定义 DAO 对象以简单地实现接口并针对接口进行编程.当您无法控制目标类时，通常会使用适配器模式.我对适配器模式的主要用途是为没有实现接口的框架类创建包装器.

Generally the adapter pattern transforms one interface into another, but it can simply wrap the behavior to isolate your class from the underlying implementation. In your case, you are using an adapter, but you could just as easily have defined the DAO objects to simply implement the interface and programmed against the interface. The adapter pattern is usually used when you don't have control over the target class. My primary use of the adapter pattern would be to create wrappers for a framework class that doesn't implement an interface.

假设我想模拟一个没有实现接口(并且没有虚拟方法)的框架类.对于许多模拟 API，这很难或不可能做到.然后，我要做的是将我自己的接口定义为我所针对的类的签名的子集.我实现了一个包装类，它实现了这个接口，并简单地将调用委托给包装的框架类.这个包装类用作框架类的适配器.我的类使用此适配器而不是框架类，但获取框架类的行为.

Say I want to mock out a framework class which doesn't implement an interface (and doesn't have virtual methods). With many mocking apis this is hard or impossible to do. What I will do, then, is define my own interface as a subset of the signature of the class I'm targeting. I implement a wrapper class that implements this interface and simply delegates the calls to the wrapped framework class. This wrapper class works as an adapter for the framework class. My classes use this adapter instead of the framework class, but get the framework class' behavior.

 public interface IFoo
 {
     void Bar();
 }

 public class FooWrapper : IFoo
 {
      private FrameworkFoo Foo { get; set; }

      public FooWrapper( FrameworkFoo foo )
      {
           this.Foo = foo;
      }

      public void Bar()
      {
           this.Foo.Bar();
      }
 }

还要考虑这样一种情况:您有几个不同的类，它们具有基本相同的功能，但具有不同的签名，并且您希望能够互换使用它们.如果您不能转换这些(或由于其他原因不想转换)，您可能需要编写一个适配器类来定义一个公共接口并在该接口的方法和目标类上可用的方法之间进行转换.

Consider also the case where you have a couple of different classes that have basically the same functionality, but different signatures and you want to be able to use them interchangeably. If you can't transform these (or don't want to for other reasons), you may want to write an adapter class that defines a common interface and translates between that interface's methods and the methods available on the target classes.

框架类:

public class TargetA
{
    public void Start() { ... }
    public void End() { ... }
}

public class TargetB
{
    public void Begin() { ... }
    public void Terminate() { ... }
}

适合他们的适配器

public interface ITargetAdapter
{
    void Open();
    void Close();
}

public class AdapterA : ITargetAdapter
{
     private TargetA A { get; set; }

     public AdapterA( TargetA a )
     {
           this.A = a;
     }

     public void Open() { this.A.Start(); }
     public void Close() { this.A.End(); }
}

public class AdapterB : ITargetAdapter
{
     private TargetB B { get; set; }

     public AdapterB( TargetB a )
     {
           this.B = a;
     }

     public void Open() { this.B.Begin(); }
     public void Close() { this.B.Terminate(); }
}

然后用作:

ITargetAdapter adapter = new AdapterA( new TargetA() );
adapter.Open();
adapter.Close();     

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