Using default parameter values with Ninject 3.0

Question

I have a class with a constructor having a parameter with a default value. With Ninject 2.2, it would honor the [Optional] attribute and work fine with no b

Answer 1

The Optional Attribute is ignored in this situation because there is always the default value available- But the provided value is null. Null is not an allowed value by default.

You can override this behavior by setting NinjectSettings.AllowNullInjection to true.

Answer 2

You can avoid setting AllowNullInjection globally while still injecting a parameter only when a binding exists by configuring your binding like this:

Kernel.Bind<IEmployeeValidator>()
      .To<EmployeeValidator>()
      .WithConstructorArgument(typeof(IValidator<PersonName>), c => c.Kernel.TryGet<IValidator<PersonName>>());

[Optional] is not needed for that.