c# ninject 在实例化的 class 中注入依赖

Question

我有一个使用 Repository Pattern 和 Ninject (DI) 的 C# MVC 项目。一切正常。

在存储库中，我正在实例化一个 class 来处理对外部 API 的一些调用，如下所示：

public class EmployeeRepository : IEmployeeRepository
    {
        private readonly AppState _appState;

        public EmployeeRepository(IAppStateProvider appStateProvider)
        {
            _appState = appStateProvider.AppState;
        }

        public bool ProcessEmployee(long employeeId, object data)
        {
            var api = new ExternalAPI(_appState);
            api.PostData(data);
            return true;
        }
}

那么我的ExternalAPI.csclass是：

public class ExternalAPI: BaseRepository
    {
        [Inject]
        public ILogRepository Logger { get; set; }

        private readonly AppState _appState;

        public ExternalAPI(AppState appState)
        {
            _appState = appState;
        }


        private bool PostData(object data)
        {
            bool returnVal = true;

            // Some code here....

            Logger.InsertLog(data); // HERE Logger IS NULL

            return returnVal;
        }
 }

我在这里遇到异常，因为 Logger 是 null。

并且在我的主项目 NinjectWebCommon.cs 文件中正确注册了依赖项：

private static void RegisterServices(IKernel kernel)
        {

            kernel.Bind(typeof(ILogRepository)).To(typeof(Data.LogRepository));
         }

Any clue why the [Inject] of ILogRepository is not working in the ExternalAPI class?

可能是因为我从 EmployeeRepository 创建了一个新实例 class:

var api = new ExternalAPI(_appState);

Any advice and how can I make the injection of ILogRepository work in ExternalAPI class?

Answer 1

引用Explicit Dependencies Principle

Methods and classes should explicitly require (typically through method parameters or constructor parameters) any collaborating objects they need in order to function correctly.

ExternalAPI 依赖于 ILogRepository 和 AppState 所以应该注入它

public class ExternalAPI: BaseRepository, IExternalAPI {

    private readonly ILogRepository logger;
    private readonly AppState _appState;

    public ExternalAPI(IAppStateProvider appStateProvidere, ILogRepository logger) {
        _appState = appStateProvidere.AppState;
        this.logger = logger;
    }


    public bool PostData(object data) {
        bool returnVal = true;

        // Some code here....

        logger.InsertLog(data); // HERE Logger IS NULL

        return returnVal;
    }
}

EmployeeRepository 依赖于 ExternalAPI，因此应该将其注入其中。

public class EmployeeRepository : IEmployeeRepository {
    private readonly IExternalAPI api;

    public EmployeeRepository(IExternalAPI api) {
        this.api = api;
    }

    public bool ProcessEmployee(long employeeId, object data) {
        api.PostData(data);
        return true;
    }
}

确保任何必要的依赖项都已注册到容器

private static void RegisterServices(IKernel kernel) {
    //...
    kernel.Bind(typeof(ILogRepository)).To(typeof(Data.LogRepository));
    kernel.Bind(typeof(IExternalAPI)).To(typeof(ExternalAPI));
    //...
 }

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