如何将另一个 class 实例传递给 controller 构造函数

Question

I am very new to the controller model concept. I am not understanding how and where to call the constructor of HomeController and how to pass student class instance?

private IStudent _student;
public HomeController(IStudent student)
{
 _student= student;
 }

public interface IStudent 
{
 // Some method
 }

Maybe, the functionality of services.AddTransient(IStudent,Student<>) I want to understand.

Answer 1

You do not call the constructor of a Controller yourself in your code. This is what the ASP.NET Framework does whenever it needs an instance of the controller to perform an action that is defined in that controller.

Your HomeController is part of an ASP.NET application running on a (web) server. A user can execute a function of this application by calling a specific URL.

For example, if the HomeController contains an Action method like this:

public ActionResult Info()
{
    // do something, then return result
    ...
    
    return View();
}

this method would be executed whenever an URL similar to http://<server>/Home/Info is called.

If you need information from a student instance inside the controller, you can pass it via dependency injection in the constructor, as it already happens in your code snippet. For this to work, IStudent must be registered with the service container. This is done in Startup.cs in the ConfigureServices method:

public void ConfigureServices(IServiceCollection services)
{
    ...
    services.AddTransient<IStudent,Student>();
    ...
}

Such a service may have different lifetimes:

• Singleton: only one instance is created, which is used over and over again
• Scoped: in a web application, a scoped service is created once per client request
• Transient: each time the service is requested from the service container, a new instance is created

Depending on what lifetime you want your service to have, you need to choose the registration method accordingly.