C＃如何使用接口 [英] C# How to use interfaces

问题描述

这是一个相对直截了当的问题。但我想知道通过使用接口访问单独项目中的方法的正确用法是什么。

This is a relatively straight forward question. But I was wondering what the correct usage is for accessing a method inside a separate project through the use of an interface.

项目： Test.ClassLibrary

界面：

public interface ITest
{
    string TestMethod();
}

等级：

public class Test : ITest
{
    public string TestMethod()
    {
        return "Test";
    }
}

项目： Test.Web

控制器：

public class HomeController : Controller
{
    private ITest test;
    public ActionResult Index()
    {
        return Content(test.TestMethod());
    }

}

以上返回的NullReferenceException 。我假设它是因为控制器到达接口，并且不知道接下来要去哪里。

The above returns a NullReferenceException. I'm assuming it's because the controller gets to the interface, and doesn't know where to go next.

解决此问题的最佳方法是什么？我是否必须在控制器中引用 Test 类，或者我可以通过仅引用 ITest ？

What's the best way to fix this? Do I have to reference the Test class in the controller or can I some how get away with only having a reference to ITest?

推荐答案

• 你永远不会实例化 ITest测试，你只声明它。


• 你的测试类不会从界面继承。


• You never instantiate ITest test, you only declare it.
• Your Test class doesn't inherit from the interface.

您需要更新您的班级声明

You need to update your class declaration

public class Test : ITest // interface inheritance 
{

在你的控制器中，实例化 test 。

And in your controller, instantiate test.

ITest test = new Test();

随着您的进一步发展，您将需要探索注入在控制器中测试实例，这样你就不会有硬依赖，而只是在接口 ITest 上。评论提及IoC或控制反转，但您应该研究各种依赖性反转技术技术（IoC是其中之一，依赖注入等）。

As you get further along, you'll want to explore techniques for injecting the Test instance into the controller so that you do not have a hard dependency upon it, but just on the interface ITest. A comment mentions IoC, or Inversion of Control, but you should look into various Dependency Inversion techniques techniques (IoC is one of them, dependency injection, etc).

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