In C# DI, is it possible to wrap (replace) a registered service with my own but still keep the old instance?

Assuming I have this service registration: services.AddScoped(); I know you can "Replace service registration in ASP.NET Core built-in DI container?" but is it possible to replace it but still keep the former instance intact like this? services.AddScoped(sp => new MyFooWrapper(/* I need the original Foo here */)); This would be helpful in case I am performing a unit test where I can decide if I want to replace, for example, an external API call or not: public class MyFooWrapper(IFoo wrapped) : IFoo { public void DoSomething() { if (TestingWithExternal) { wrapped.DoSomething(); // Original method that calls external HTTP API } else { FakeSomething(); } } } Another use-case is that I want to wrap Blazor's IJSRuntime since MS makes it very difficult to change its behaviors as the implementation is internal and re-implement everything is just very difficult in case they update it. Thanks to the answer, this is the code that can replace multiple services as well // Replace with fakes foreach (var s in services.ToList()) { // Other logic if (s.ServiceType == typeof(IOaApiService)) { services.Remove(s); var implType = s.ImplementationType; ArgumentNullException.ThrowIfNull(implType); services.Add(new(implType, implType, s.Lifetime)); services.Add(new( s.ServiceType, sp => new FakeOaAiService((IOaApiService)sp.GetRequiredService(implType)), s.Lifetime)); } }

Marayaty Marayaty
Aug 28, 2024 - 03:45
0 9
In C# DI, is it possible to wrap (replace) a registered service with my own but still keep the old instance?

Assuming I have this service registration: 

services.AddScoped();

I know you can "Replace service registration in ASP.NET Core built-in DI container?" but is it possible to replace it but still keep the former instance intact like this? 

services.AddScoped(sp => new MyFooWrapper(/* I need the original Foo here */));

This would be helpful in case I am performing a unit test where I can decide if I want to replace, for example, an external API call or not: 

public class MyFooWrapper(IFoo wrapped) : IFoo
{
    
    public void DoSomething()
    {
        if (TestingWithExternal)
        {
            wrapped.DoSomething(); // Original method that calls external HTTP API
        }
        else
        {
            FakeSomething();
        }
    }

}

Another use-case is that I want to wrap Blazor's IJSRuntime since MS makes it very difficult to change its behaviors as the implementation is internal and re-implement everything is just very difficult in case they update it.

Thanks to the answer, this is the code that can replace multiple services as well 

// Replace with fakes
foreach (var s in services.ToList())
{
    // Other logic
    if (s.ServiceType == typeof(IOaApiService))
    {
        services.Remove(s);

        var implType = s.ImplementationType;
        ArgumentNullException.ThrowIfNull(implType);

        services.Add(new(implType, implType, s.Lifetime));
        services.Add(new(
            s.ServiceType,
            sp => new FakeOaAiService((IOaApiService)sp.GetRequiredService(implType)),
            s.Lifetime));
    }
}
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