Ninject: Bind Constructor Argument to Property of Other Object

c#, ninject

Solution

You are on the right track:

The `Kernel.Get<T>()` method is an extension method defined on the `ResolutionExtensions` in the `Ninject` namepsace so with adding the `using Ninject;` it is available in your module as well.

But instead of the `Module.Kernel` you should use the `IContext` provided in the second overload of `WithConstructorArgument` to get the `Kernel`:

Bind<IFoo>().To<Foo>()
    .WithConstructorArgument("username", 
                             context => context.Kernel.Get<IConfig>().Username)
    .WithConstructorArgument("password", 
                             context => context.Kernel.Get<IConfig>().Password);

Problem

I have an `IConfig` object that contains settings used throughout my application. At the moment, I inject the entire object into the constructor of each object that needs it, as follows: ``` public interface IConfig { string Username { get; } string Password { get; } //... other settings } public class Foo : IFoo { private readonly string username; private readonly string password; public Foo(IConfig config) { this.username = config.Username; this.password = config.Password; } } ``` The downside is that `IConfig` contains a large number of settings because it's deserialised from an overall config file, so injecting the entire object is unnecessary. What I'd like to do is change the constructor to `Foo(string username, string password)` so that it only receives the settings it needs. This also makes creating `Foo` objects for testing much easier (not having to set up `IConfig` just to create `Foo`). I'd like to bind the constructor arguments directly in my `NinjectModule`, something like the following: ``` public class MyModule : NinjectModule { public override void Load() { Bind<IConfig>().To<JsonConfig>() .InSingletonScope(); Bind<IFoo>().To<Foo>() .WithConstructorArgument("username", IConfig.Username) .WithConstructorArgument("password", IConfig.Password); } } ``` Obviously this code doesn't work, but how would I go about doing what I wanted? My original idea was to use the `NinjectModule.Kernel` to get the `IKernel` then get an instance of my `IConfig` object and inject the properties as required, but the object returned by `NinjectModule.Kernel` has no `Get<T>()` method.

Original source