create nuget package support the dependency injection DI

Question

i am creating a Nuget Package should supports the dependency injection (DI) throw a service called "IGETSum" with one method called "SUMorSUB" that’s take a two numbers and sum them or subtract them. every thing is done except call the method in program.cs, calling the method in program.cs should contains options and be like :

builder.Services.SUMorSUB(opt => opt.operation = "+");

the option "operation" will specify which operation will be done. either SUM(+) or SUB(-).

below is the package code

using System;

namespace IGETSum
{
    public class SumNuget
    {
        public string operation;
        public int SUMorSUB(int num1,int num2) {
            var res=0;
            if (operation == "+")
            {
                res= num1+ num2;
            }
            else
            {
                res = num1 - num2;

            }

            return 0; 
        
        }
    }
}

the main reason of this question is to know how to make the nuget support Dependency Injection (DI) and to know how to add options. any help is highly appreciated.

Answer 1

There are different ways consumers of your library can register your service for use in their application. The way you've likely consumed other libraries that integrate with DI is by calling an extension method provided for IServiceCollection.

For example, here's an extension method to register your SumNuget class:

public static class IServiceCollectionExtensions
{
    public static void AddSumOrSub (this IServiceCollection services)
    {
        services.AddSingleton<SumNuget>();
    }
}

Which can then be invoked as:

services.AddSumOrSub();

To go a bit further and provide a way to configure the options for your service, there are a couple different ways you can go. I would suggest reading the configuration documentation, and suggest implementing the behaviour with the "options pattern".

The following I'm typing without running at all - so I recommend reading the above documentation rather than the code I'm writing on the fly in Stack Overflow's editor. I make no guarantees on its correctness

We change SumNuget to have IOptions<SumNugetOptions> injected, which it uses to determine its behaviour:

public class SumNuget
{
    private readonly IOptions<SumNugetOptions> _options;

    public SumNuget(IOptions<SumNugetOptions> options){
        _options = options;
    }

    public int SUMorSUB(int num1,int num2) {
        var res = 0;
        if (_options.Value.operation == "+")
        {
            res= num1 + num2;
        }
        else
        {
            res = num1 - num2;
        }
        return 0; 
    }
}

You can imagine some SumNugetOptions object with a string type operation property on it.

Then in your extension method:

public static class IServiceCollectionExtensions
{
    public static void AddSumOrSub (this IServiceCollection services, Action<SumNugetOptions> optionsProvider)
    {
        services.Configure<SumNugetOptions>(optionsProvider);
        services.AddSingleton<SumNuget>();
    }
}

Hopefully the above gives you some direction on how this can be achieved.

P.S. You might want to return res rather than 0 in SUMorSUB