c# - Web API Controller 的构造函数是如何调用的？

Question

根据 this article , Controller 应该有一个构造函数来获取传入的要实现的接口(interface)，a la:

public class DuckbillsController : ApiController
{
    IDuckbillRepository _platypiRepository;

    public DuckbillsController(IDuckbillRepository platypiRepository)
    {
        if (platypiRepository == null)
        {
            throw new ArgumentNullException("platypiRepository is null");
        }
        _platypiRepository = platypiRepository;
    }
}

但是这个构造器是怎么调用的呢？通过客户端调用此类中包含的 Web API 方法进行计算，但它如何传递接口(interface)类型？还是不必发生(构造函数未被任何人/从任何地方显式调用)？

更新

规范示例显示在接口(interface)声明前面加上“private readonly”，但这不是编译所必需的。是否有编译，我的意思是令人信服的理由，让我在前面加上“私有(private)只读”？

Answer 1

因为在任何地方都没有这方面的文档(官方文档只是讨论如何使用 Unity)。这是你如何做的。

HttpConfiguration.DependencyResolver 属性是 IDependecyResolver 的一个实例，它基本上是一个服务定位器(您需要一个类型的实例，它知道如何创建它) .我想要的是提供我自己的 Controller 实例化。

像这样使用:

config.DependencyResolver = 
   new OverriddenWebApiDependencyResolver(config.DependencyResolver)
   .Add(typeof(ScoreboardController), () => 
                                    new ScoreboardController(Messages) 
   ); 

这样实现:

/// <summary>
/// The standard web api dependency resolver cannot inject dependencies into a controller 
/// use this as a simple makeshift IoC
/// </summary>
public class OverriddenWebApiDependencyResolver : WebApiOverrideDependency<IDependencyResolver >, IDependencyResolver {
    public OverriddenWebApiDependencyResolver Add(Type serviceType, Func<object> initializer) {
        provided.Add(serviceType, initializer);
        return this;
    }
    public IDependencyScope BeginScope() => new Scope(inner.BeginScope(), provided);
    public OverriddenWebApiDependencyResolver(IDependencyResolver inner) : base(inner, new Dictionary<Type, Func<object>>()) { }
    public class Scope : WebApiOverrideDependency<IDependencyScope>, IDependencyScope {
        public Scope(IDependencyScope inner, IDictionary<Type, Func<object>> provided) : base(inner, provided) { }
    }
}
public abstract class WebApiOverrideDependency<T> : IDependencyScope where T : IDependencyScope {
    public void Dispose() => inner.Dispose();
    public Object GetService(Type serviceType) {
        Func<Object> res;
        return provided.TryGetValue(serviceType, out res) ? res() : inner.GetService(serviceType);
    }

    public IEnumerable<Object> GetServices(Type serviceType) {
        Func<Object> res;
        return inner.GetServices(serviceType).Concat(provided.TryGetValue(serviceType, out res) ? new[] { res()} : Enumerable.Empty<object>());
    }
    protected readonly T inner;
    protected readonly IDictionary<Type, Func<object>> provided;
    public WebApiOverrideDependency(T inner, IDictionary<Type, Func<object>> provided) {
        this.inner = inner;
        this.provided = provided;
    }

}

诀窍在于您实际上必须实现 IDependencyScope 两次 - 一次用于 IDependencyResolver ，一次用于它在每个请求上创建的范围。