c# - Asp.net MVC 样板依赖注入(inject)不起作用

Question

我正在玩 Asp.Net MVC 6 boilerplate项目。我正在尝试为我的一项服务配置依赖项注入(inject)。内置的 IoC 容器似乎忽略了我的绑定(bind)。

启动.cs

public void ConfigureServices(IServiceCollection services){
    /*boilerplate's default bindings*/
    services.AddTransient<IDummy, Dummy>(p => new Dummy()
        {
            name = "from injection"
        });
}

HomeController.cs

public IActionResult Index(IDummy dummy){
    var test = dummy.name;
    return this.View(HomeControllerAction.Index);
}

异常(exception):

ArgumentException: Type 'Presentation.WebUI.Controllers.IDummy' does not have a default constructor

你能告诉我我做错了什么吗？

Answer 1

该异常是因为框架无法将操作参数绑定(bind)到接口(interface)。

当框架默认使用构造函数注入(inject)时，您正在尝试对 Action 进行注入(inject)。

引用:Dependency Injection and Controllers

Constructor Injection

ASP.NET Core’s built-in support for constructor-based dependency injection extends to MVC controllers. By simply adding a service type to your controller as a constructor parameter, ASP.NET Core will attempt to resolve that type using its built in service container.

public class HomeController : Controller {
    IDummy dummy;
    public HomeController(IDummy dummy) {
        this.dummy = dummy
    }

    public IActionResult Index(){
        var test = dummy.name;
        return this.View(HomeControllerAction.Index);
    }
}

ASP.NET Core MVC controllers should request their dependencies explicitly via their constructors. In some instances, individual controller actions may require a service, and it may not make sense to request at the controller level. In this case, you can also choose to inject a service as a parameter on the action method.

Action Injection with FromServices

Sometimes you don’t need a service for more than one action within your controller. In this case, it may make sense to inject the service as a parameter to the action method. This is done by marking the parameter with the attribute [FromServices] as shown here:

public IActionResult Index([FromServices] IDummy dummy) {
    var test = dummy.name;
    return this.View(HomeControllerAction.Index);
}