通过依赖注入执行我的类函数

Question

我一直在努力将我的紧耦合方法转换成可以进行单元测试的方法,并在这里寻求一些建议.由于一些建议,我现在让我的方法通过它的单元测试 - 但是我现在发现我无法从我的应用程序中调用该方法.我曾经从控制器访问我的GetAllProductsFromCSV()方法,具体如下:

    public ActionResult Index()
    {
        var products = new ProductsCSV();
        List<ProductItem> allProducts = products.GetAllProductsFromCSV();

        foreach (var product in allProducts)
        {
            if (string.IsNullOrEmpty(product.ImagePath))
            {
                product.ImagePath = "blank.jpg";
            }
        }

        return View(allProducts);
    }

方法如下:

public class ProductsCSV
{
    public List<ProductItem> GetAllProductsFromCSV()
    {
        var productFilePath = HttpContext.Current.Server.MapPath(@"~/CSV/products.csv");

        String[] csvData = File.ReadAllLines(productFilePath);

        List<ProductItem> result = new List<ProductItem>();

        foreach (string csvrow in csvData)
        {
            var fields = csvrow.Split(',');
            ProductItem prod = new ProductItem()
            {
                ID = Convert.ToInt32(fields[0]),
                Description = fields[1],
                Item = fields[2][0],
                Price = Convert.ToDecimal(fields[3]),
                ImagePath = fields[4],
                Barcode = fields[5]
            };
            result.Add(prod);
        }
        return result;
    }
}

我现在在ProductCSV类中进行了以下更改:

public class ProductsCSV
{
    private readonly IProductsCsvReader reader;

    public ProductsCSV(IProductsCsvReader reader = null)
    {
        this.reader = reader;
    }

    public List<ProductItem> GetAllProductsFromCSV()
    {
        var productFilePath = @"~/CSV/products.csv";
        var csvData = reader.ReadAllLines(productFilePath);
        var result = parseProducts(csvData);
        return result;
    }


    private List<ProductItem> parseProducts(String[] csvData)
    {
        List<ProductItem> result = new List<ProductItem>();

        foreach (string csvrow in csvData)
        {
            var fields = csvrow.Split(',');
            ProductItem prod = new ProductItem()
            {
                ID = Convert.ToInt32(fields[0]),
                Description = fields[1],
                Item = fields[2][0],
                Price = Convert.ToDecimal(fields[3]),
                ImagePath = fields[4],
                Barcode = fields[5]
            };
            result.Add(prod);
        }
        return result;
    }

以及以下类和接口:

public class DefaultProductsCsvReader : IProductsCsvReader
{
    public string[] ReadAllLines(string virtualPath)
    {
        var productFilePath = HostingEnvironment.MapPath(virtualPath);
        String[] csvData = File.ReadAllLines(productFilePath);
        return csvData;
    }
}

public interface IProductsCsvReader
{
    string[] ReadAllLines(string virtualPath);
}

正如我所说,方法GetAllProductsFromCSV上的单元测试现在成功完成,但是当我尝试从我的控制器访问该方法时,我在GetAllProductsFromCSV中的reader.ReadAllLines调用上得到NullReferenceException.当我尝试从控制器中创建ProductsCSV的实例时,我有意义 - 我没有传递任何参数......但是该类的构造函数请求IProductsCsvReader.我无法弄清楚的是我现在如何实际调用该方法？我希望很清楚？

Answer 1

首先让更新ProductsCSV具有后备接口

public interface IProductsCSV {
    List<ProductItem> GetAllProductsFromCSV();
}

public class ProductsCSV : IProductsCSV {
    //...other code removed for brevity
}

控制器现在依赖于上面介绍的抽象,将其与具体实现与原始控制器分离.虽然是一个简化的例子,但它允许控制器更容易维护和单独测试.

public class ProductsController : Controller {
    private readonly IProductsCSV products;

    public ProductsController(IProductsCSV products) {
        this.products = products;
    }

    public ActionResult Index() {
        List<ProductItem> allProducts = products.GetAllProductsFromCSV();    
        foreach (var product in allProducts) {
            if (string.IsNullOrEmpty(product.ImagePath)) {
                product.ImagePath = "blank.jpg";
            }
        }    
        return View(allProducts);
    }
}

请注意该操作如何与之前的操作完全匹配,除了products创建方式.

最后,现在控制器已经被重构为依赖性反转,需要将框架配置为能够在请求时将依赖项注入控制器.

您最终可以使用您选择的库,但对于此示例,我使用的是他们在文档中使用的内容

ASP.NET MVC 4依赖注入

别介意这个版本.实施是可转让的.

在上面的文档中,他们使用Unity作为他们的IoC容器.有许多容器库可供使用,因此请搜索您喜欢的容器库并使用它.

public static class BootStrapper {

    private static IUnityContainer BuildUnityContainer() {
        var container = new UnityContainer();

        //Register types with Unity
        container.RegisterType<IProductsCSV , ProductsCSV>();
        container.RegisterType<IProductsCsvReader, DefaultProductsCsvReader>();

        return container;
    }

    public static void Initialise() {
        //create container
        var container = BuildUnityContainer();
        //grab the current resolver
        IDependencyResolver resolver = DependencyResolver.Current;
        //create the new resolver that will be used to replace the current one
        IDependencyResolver newResolver = new UnityDependencyResolver(container, resolver);
        //assign the new resolver.
        DependencyResolver.SetResolver(newResolver);
    }
}

public class UnityDependencyResolver : IDependencyResolver {
    private IUnityContainer container; 
    private IDependencyResolver resolver;

    public UnityDependencyResolver(IUnityContainer container, IDependencyResolver resolver) {
        this.container = container;
        this.resolver = resolver;
    }

    public object GetService(Type serviceType) {
        try {
            return this.container.Resolve(serviceType);
        } catch {
            return this.resolver.GetService(serviceType);
        }
    }

    public IEnumerable<object> GetServices(Type serviceType) {
        try {
            return this.container.ResolveAll(serviceType);
        } catch {
            return this.resolver.GetServices(serviceType);
        }
    }
 }

您可以在启动代码中调用上述引导程序.

例如

protected void Application_Start() {
    AreaRegistration.RegisterAllAreas();    
    WebApiConfig.Register(GlobalConfiguration.Configuration);
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
    BundleConfig.RegisterBundles(BundleTable.Bundles);

    Bootstrapper.Initialise(); //<-- configure DI

    AppConfig.Configure();
}

所以现在当框架必须创建时,ProductsController它将知道如何初始化和注入控制器的依赖项.