如何使用参数配置mvc core 2依赖项注入，其中参数之一是依赖项？

Question

If I have:

public CatManager(ICatCastle catCastle, int something)

I want to set this up to be dependency injected, but I am not sure how.

I think I can do this:

services.AddScoped<ICatCastle, CatCastle>();

services.AddScoped<ICatManager>(new CatManager(???, 42));

But I am not sure what to put in as the ??? to get the CatCastle. I'd like it to resolve a new CatCastle every time CatManager is injected.

As a further step, I wonder if it possible to do something like:

public CatManager(int something)

services.AddScoped<ICatManager>(new CatManager(ResolveICatCastleIntoCatCastle().SomeID));

So that CatManager's constructor is automatically invoked with the ID, but not the object that gets the IDs. For example, if it is a database connection I want that resolution to occur when it is created and not later on when the property is actually accessed.

Answer 1

You can use the factory delegate overload.

Like

services.AddScoped<ICatManager>(serviceProvider => 
    new CatManager(serviceProvider.GetRequiredService<ICatCastle>(), 42));

I'd like it to resolve a new CatCastle every time CatManager is injected.

If you want a new castle then you need to register CatCastle with a transient scope

services.AddTransient<ICatCastle, CatCastle>();

Regarding the further step public CatManager(int something) , a similar approach can be done

services.AddScoped<ICatManager>(serviceProvider => 
    new CatManager(serviceProvider.GetRequiredService<ICatCastle>().SomeID));

where the dependency is resolved and what ever action is performed before injecting it into the dependent class.

Answer 2

You should wrap the value 42 in a component-specific configuration class and register and inject that configuration object instead.

For instance:

public class CatSettings
{
    public readonly int AnswerToAllCats;
    public CatSettings(int answerToAllCats) => AnswerToAllCats = answerToAllCats;
}

public class CatManager : ICatManager
{
    public CatManager(ICatCastle castle, CatSettings settings) ...
}

The configuration would then look like

services.AddScoped<ICatManager, CatManager>();
services.AddSingleton(new CatSettings(42));