在 ASP.NET Core 中的方法中注入依賴

Question

我有以下場景：我得到了一個服務ICompanyDocumentsService ，其中有一個我在Startup類中注冊的單一實現CompanyDocumentsService ：

 public void ConfigureServices(IServiceCollection services)
        {
            services.AddScoped<ICompanyDocumentService, CompanyDocumentService>();
        }

我在很多地方都需要這個服務，在 Constructor 中使用 DI 並不會打擾我。 但是，有一個地方我需要在方法中注入它（或者可能在屬性中會更好）：

            public abstract class CompanyDocumentBase
            {
                public abstract object GetAllProperties(Employee employee, string properties, 
                      CompanyDocumentReferenceData documentReferenceData);
                // blah, blah, lots of Formatting Methods


                private CompanyDocumentService CompanyDocumentService { get; set; } // **inject service here**

                public string GetFormattedEmployeeIndividualEmploymentAgreementNumber(Employee employee, 
                    ICompanyDocumentService companyDocumentService = null) // **optional because 
//inherited class doesn't need to know anything about this service, it concerns only it's result**
                {
                    companyDocumentService = CompanyDocumentService;
                    var test  = 
                       companyDocumentService.GetEmloyeeIndividualEmploymentAgreementNumber(employee.Id);


                    return string.Empty;
                }

            }

有很多繼承CompanyDocumentBase類只關心它的方法結果，如上所述，這就是為什么該參數是可選的，這就是為什么我不需要在構造函數中注入 DI，因此繼承類將不需要那個。

 public class JobDescriptionCompanyDocument : CompanyDocumentBase
    {
        public override object GetAllProperties(Employee employee,
            string properties, CompanyDocumentReferenceData documentReferenceData)
        {
            var document = JsonConvert.DeserializeObject<JobDescriptionModel>(properties);

            document.IndividualEmploymentAgreementNumber = GetEmployeeIndividualEmploymentAgreementNumber(employee);

            return document;
        }
    }

有什么簡單的方法可以實現這一目標嗎？ 最好不需要安裝單獨的庫，如 Unity 或 Autofac。 理想的做法是以某種方式將CompanyDocumentsService的實例直接放入該屬性中，例如：

private CompanyDocumentService CompanyDocumentService => Startup.Services.blah that instance

Answer 1

一種 hack 方式（我個人不推薦它）是在構建容器之后，您可以解析IHttpContextAccessor的實例並將其設置為靜態類，例如IoC

然后你可以做private CompanyDocumentService CompanyDocumentService => IoC.HttpContextAccessor.HttpContext.RequestServices.GetService() 。

https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.httpcontext.requestservices?view=aspnetcore-3.1

該接口是一個單例，並提供從靜態上下文對范圍服務的訪問。

請注意，您可能必須明確注冊 HttpContextAccessor： https ://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-context ? view = aspnetcore-3.1

更新

我會推薦什么

如果您對對象工廠持開放態度，並改變了DocumentBase的實例化方式，請嘗試創建一個工廠，並且每當您需要DocumentBase的實例時，只使用工廠來創建它：

public abstract class CompanyDocumentBase
{
    // Use internal so that access only limited to friendly assembly
    internal CompanyDocumentService CompanyDocumentService { get; set; }
}

// Inject this class to where you need to create an instance of CompanyDocumentBase
public class CompanyDocumentFactory<T> where T : CompanyDocumentBase
{
    private readonly IServiceProvider _services;

    // DI contaiener has implicit IServiceProvider support, when you do this on constructor, it injects service provider of *current* scope
    // If this factory is registered as singleton, you need to use IHttpContextAccessor to use request's service provider in Create method
    // because your DocumentService is scoped.
    public CompanyDocumentFactory(IServiceProvider services)
    {
        _services = services;
    }

    public T Create()
    {
        // Create an instance of document use your current method.
        var instance = new T();
        instance.CompanyDocumentService = _services.GetRequiredService<ICompanyDocumentService>();
        return instance;
    }
}