How to register a generic dependency in Autofac when I dont know the Types in advance?

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In the below program, I am trying to figure out a way of I can register the instance and instance1 as singleton dependency in Autofac. In the main function, I only get the types as "ActualType" so I have to use MakeGeneric to create an instance from them.

Can someone please take a look at this?

void Main()
{
    string type1 = "System.String";
    string type2 = "System.String";

    Type columnFetcherType = typeof(Foo<,>).MakeGenericType(Type.GetType(type1), Type.GetType(type2));
    ConstructorInfo ctor = columnFetcherType.GetConstructors().FirstOrDefault();
    var instance1 = ctor.Invoke(new object[] { 1, 2 });

    // I want to register instance1 as singleton with Autofac, so that when I resolve Test, It will inject the Foo<string, string> instance which I registered.

    type1 = "System.Int32";
    type2 = "System.Int32";

    columnFetcherType = typeof(Foo<,>).MakeGenericType(Type.GetType(type1), Type.GetType(type2));
    ctor = columnFetcherType.GetConstructors().FirstOrDefault();
    var instance2 = ctor.Invoke(new object[] { 1, 2 });

    // I want to register instance2 as singleton with Autofac, so that when I resolve Test1, It will inject the Foo<int, int> instance which I registered.

}

// You can define other methods, fields, classes and namespaces here


public interface IFoo<Tkey,Tvalue> 
{
    void Print();
}

public class Foo<Tkey, Tvalue> : IFoo<Tkey, Tvalue>
{
    private int _a ;
    private int _b ;
    
    public Foo(int a, int b)
    {
        this._a = a;
        this._b = b;
    }
    
    public void Print()
    {
        Console.WriteLine(this.GetType());
    }
}

public interface ITest {}

public class Test : ITest
{
    IFoo<string, string> _param1;
    
    public Test(IFoo<string, string> param1)
    {
        this._param1 = param1;
    }
}

public class Test1 : ITest
{
    IFoo<int, int> _param1;

    public Test1(IFoo<int, int> param1)
    {
        this._param1 = param1;
    }
}

Thanks Bunch.

autofac dependency-injection c#
1 Answers

It isn't much different from registering with the generics, you just need to do more work with reflection and types. You almost had it.

I'll show you how to do one; the others are the exact same pattern.

// The trick here is that you need...
// - the concrete object type
// - the constructor (so you can create the instance)
// - the instance
// - the interface type (because the constructor parameter isn't a Foo<T,U>, it's IFoo<T,U>)
// ...so:

// Get the generic parameter.
var stringType = Type.GetType("System.String");

// Get the concrete type.
var closedGeneric = typeof(Foo<,>).MakeGenericType(stringType, stringType);

// Get the constructor.
var ctor = closedGeneric.GetConstructors()[0];

// Create your instance.
var instance = ctor.Invoke(new object[] { 1, 2 });

// Get the interface that the constructor wants.
var interfaceType = typeof(IFoo<,>).MakeGenericType(stringType, stringType);

// Now...
var builder = new ContainerBuilder();

// Register the thing that consumes the instance.
builder.RegisterType<Test>();

// Register your instance, but add the .As() so you can resolve as the interface.
builder.RegisterInstance(instance).As(interfaceType);

// Build and resolve. Done!
var container = builder.Build();
container.Resolve<Test>();
Travis_Illig_81160
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