IServiceCollection覆盖一个构造函数参数

问题描述

我有一个类，它需要三个构造函数。在我的组合根中，我想定义/覆盖三个构造函数参数中的一个其他两个依赖关系已经映射到我的DI容器中，应该从IServiceProvider创建。

与Ninject我可以这样做：

 绑定< IMyInterface>（）。到< MyClass>（）
 .WithConstructorArgument（constructorArgumentName，x =>constructor argument value ）; 
  

当Ninject创建MyClass时，它使用此字符串参数，并自动为我注入其他两个依赖项。我在.net核心遇到的问题是，我不能告诉IServiceCollection我只想指定三个参数之一，我必须定义所有这些或没有。例如，在.net核心中，这是我必须做的：

  services.AddTransient< IMyInterface>（x =>新的MyClass（constructor argument value，new Dependency2（），new Dependency3（））; 
  

不喜欢创建Dependency2和Dependency3类的新实例;这两个类可以有自己的构造函数参数，我只是想DI来管理这些依赖关系，所以我的问题是 - 如何覆盖一个构造函数参数使用IServiceCollection类映射依赖于.net core？

如果不能仅覆盖一个引用参数，那么如何解决与IServiceCollection的依赖关系？做这样的事情：

  services.AddTransient< IMyInterface>（x => new MyClass（constructor argument value，serviceCollection .Resolve< IDependency2>（），serviceCollection.Resolve（IDependency3>（））; 
  

但是这不行，我无法弄清楚如何使用IServiceCollection解析依赖关系。

解决方案

尝试这样：

  services.AddTransient< IDependency2，Dependency2Impl>（） 
 
 services.AddTransient< IDependency3，Dependency3Impl>（）; 
 
 services.AddTransient< IMyInterface>（provider => 
 return new MyClass（constructor argument value，
 provider.GetService< IDependency2>（），
 provider.GetService< IDependency3>（））; 
）; 
  

I have a class that takes three constructor arguments. In my composition root I want to define/override only one of the three constructor arguments; the other two dependencies have already been mapped in my DI container and should get created from the IServiceProvider.

With Ninject I could do something like this:

Bind<IMyInterface>().To<MyClass>()    
    .WithConstructorArgument("constructorArgumentName", x => "constructor argument value");

When Ninject creates MyClass it uses this string parameter and automatically injects the other two dependencies for me. The problem I'm experiencing in .net core is that I cannot tell the IServiceCollection I only want to specify one of the three arguments, I have to define all of them or none. For example, in .net core this is what I have to do:

services.AddTransient<IMyInterface>(x=> new MyClass("constructor argument value", new Dependency2(), new Dependency3());

I don't like having to create new instances of the Dependency2 and Dependency3 classes; these two classes could have their own constructor arguments. I just want the DI to manage those dependencies. So my question is - how do you override a single constructor argument when mapping dependencies in .net core using the IServiceCollection class?

If you can't override just a single contructor argument then how do you resolve a dependency with the IServiceCollection? I tried doing something like this:

services.AddTransient<IMyInterface>(x=> new MyClass("constructor argument value", serviceCollection.Resolve<IDependency2>(), serviceCollection.Resolve(IDependency3>());

But this didn't work, and I couldn't figure out how to resolve dependencies using the IServiceCollection.

解决方案

Try this:

services.AddTransient<IDependency2, Dependency2Impl>();

services.AddTransient<IDependency3, Dependency3Impl>();

services.AddTransient<IMyInterface>(provider=>
    return new MyClass("constructor argument value",
      provider.GetService<IDependency2>(),
      provider.GetService<IDependency3>());
);

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