如何构造函数 - 注入仅在运行时已知的字符串？ （温莎城堡）

Question

I have class that has dependency on string:

public class Person
{
    private readonly string _name;

    public Person(string name)
    {
        if (name == null) throw new ArgumentNullException("name");
        _name = name;
    }
}

This string 'name' is known only at runtime, eg. it is defined in configuration. So I have this interface that provides this string:

public interface IConfiguration
{
    string Name { get; }
}

Both types, Person and IConfiguration (with its implementation which is not important here) are registered with Windsor container.

Question: how can I tell WindsorCastle container that it should inject the Name property of IConfiguration to the constructor of Person class?

Caveat: I don't want to inject IConfiguration to Person class or use typed factories... the Person class must be simple and accept only string as parameter.

Answer 1

There are probably more ways to do this since Windsor is ridiculously flexible, but here are three off the top of my head:

Option 1:

If IConfiguration is a singleton or somehow can populate Name without any other assistance, you could do the following:

container.Register(Component.For<IConfiguration>().ImplementedBy<Configuration>());
container.Register(Component
    .For<Person>()
    .DynamicParameters((DynamicParametersDelegate)ResolvePersonName));

// This should be a private method in your bootstrapper 
void ResolvePersonName(IKernel kernel, IDictionary parameters)
{
    parameters["name"] = kernel.Resolve<IConfiguration>().Name;
}

This method is invoked before resolving the Person , and is setting the name key/value pair to be the desired value. Windsor then uses this dictionary to override any dependencies in the constructor. I'd probably just make it a lambda to be terser:

    .DynamicParameters((k,p) => p["name"] = k.Resolve<IConfiguration>().Name));

Option 2:

If the Name value is actually defined in the applications settings file, Windsor has a built-in option for that:

container.Register(
    Component.For<Person>()
    .DependsOn(Dependency.OnAppSettingsValue("name", "configSettingKeyName")));

Option 3:

You say you don't want to use Typed Factories , but I think this is a reasonable siutation for using one. It wouldn't complicate the Person class at all, but it would add a bit to the code creating the Person objects (people?). Here's an example:

Define the factory interface:

public interface IPersonFactory
{
    Person Create(string name);
}

Then where you are creating your Person , inject the factory and use that instead:

public class PersonUser
{
    public Personuser(IConfiguration configuration, IPersonFactory personFactory)
    {
        Person person = personFactory.Create(configuration.Name);
    }
}

You'll have to add the facility and register the interface, but it's easy:

container.AddFacility<TypedFactoryFacility>();
container.Register(Component.For<IPersonFactory>().AsFactory());