Code Behavior explanation in dependency aspnet core

Question

I'm knew in dependency injection, so I was testing it. I tested constructor injection in Console Application and it went good.
So I decide to test in AspNet Core. I realized it already had something built in for that, so I don't need to install and additional package.

So, my first code was running okay and I understood it what it happend.
This is my first code:

public interface ITea  
    {  
        string Flavour();  
    }  
  
    public class LemonTea : ITea  
    {  
  
        public string Flavour()  
        {  
            return "Lemon";  
        }  
   
    }  
  
    public class TamarindoTea : ITea  
    {  
        public string Flavour()  
        {  
            return "Tamarindo";  
        }  
    }  
public class Tea   
    {  
        private ITea _tea;  
  
        //ctor injection  
        public Tea(ITea tea)  
        {  
            this._tea = tea;  
              
        }  
        public string GetFlavour()  
        {  
            return _tea.Flavour();  
        }  
  
   
    }  

now in Startup.cs

    public void ConfigureServices(IServiceCollection services)  
        {  
            services.AddControllersWithViews();  
   
            services.AddScoped<ITea, TamarindoTea>();  
            services.AddScoped<ITea, LemonTea>();  
                         
        }  

in HomeController

 public IActionResult Index()  
        {  
var tea = new Tea(_tea);  
            ViewBag.Test = tea.GetFlavour();  
              
   
            return View();  
        }  

as a result I had

I've realized that the "type of flavour" I was having was according the last Added code in ConfigureServices.
So I decide to find I way to get a result similar to this code (I also wrote it)
In index...

ITea lemon = new LemonTea();  
            ITea tamarindo = new TamarindoTea();  
               
            var tea = new Tea(tamarindo);  
            ViewBag.Test = tea.GetFlavour();  

The output here would depend on the type of ITea I inject in the constructor.
I don't know where I read, but something got me thinking that I was having too much dependencies in the second code
I was using ITea, Tea, LemonTea and TamarindoTea
So I excluded Tea, and added constructor dependency on the two other

public class LemonTea : ITea  
    {  
  
        private ITea _tea;  
        public LemonTea(ITea tea)  
        {  
            _tea = tea;  
  
        }  
  
        public string Flavour()  
        {  
            return "Lemon";  
        }  
   
    }  

But for that to work, I would have to remove the code for ConfigureServices or else I had this error

Then I thought that something was wrong (that what I think), I mean can choose the type of tea at runtime, but I now I have to instatiate the class. It was the same as I do without caring about dependency injection (besides the fact that my class don't depend on other concrete classes)

Since I'm thinking that my code is wrong, I Google to how to inject different implementations in Aspnet core
I found this code from StackOverFlow and refactor it, I also had to refactor my code because of some errors
my refactor ended up like this:

  public class LemonTea : ITea  
    {  
  
             public string Flavour()  
        {  
            return "Lemon";  
        }  
   
    }  
  
    public class TamarindoTea : ITea  
    {  
          
        public string Flavour()  
        {  
            return "Tamarindo";  
        }  
    }  
  
--------------------Startup.cs  
 public void ConfigureServices(IServiceCollection services)  
        {  
            services.AddControllersWithViews();  
            services.AddTransient<LemonTea>();  
            services.AddTransient<TamarindoTea>();  
  
        }  
  
--------------------HomeController  
 private readonly IServiceProvider _serviceProvider;  
         
        public HomeController(ILogger<HomeController> logger, IServiceProvider serviceProvider)  
        {  
            _logger = logger;  
                        _serviceProvider = serviceProvider;  
              
        }  
  
  
        public string GetTeaFlavour(string name)  
        {  
            if (name.ToLower() == nameof(LemonTea).ToLower())  
                return _serviceProvider.GetService<LemonTea>().Flavour();  
            
            else  
                return _serviceProvider.GetService<TamarindoTea>().Flavour();  
        }  
  
  public IActionResult Index()  
        {  
  
   
            ViewBag.Test =  GetTeaFlavour(nameof(TamarindoTea));  
  
       }  

I've archieved what I want, I just need to type the name of the class, and since I'm using nameof, I can refactor
So I was having some error so I've refactor my code in other to work.
In this case I didn't refactor because I knew what I was doing, I just knew how to find the solution. At some point I was understanding
what I was doing, then I got lost.

It's working, but I can't understand my code, I know how it works, but I don't know why. IFAIK that's very common for programmers
But I would like to have someone to explain to me what I've done and using my code (if possible, what would be the best implementation)

Answer 1

DI is about what is talked about in the link.

https://ardalis.com/new-is-glue/

DI is about writing clean code

https://learn.microsoft.com/en-us/archive/msdn-magazine/2016/may/asp-net-writing-clean-code-in-asp-net-core-with-dependency-injection

Github ASP.NET Core solution using DI.

https://github.com/darnold924/PublishingCompany

https://www.c-sharpcorner.com/blogs/understanding-interfaces-via-loose-coupling-and-tight-coupling

HTH