Is there a better way than this to inject a function into an object in Unity?

debugcn 投稿 Dev

AlfredBr

I'm a Unity noob, and I have a question. I want to inject an IAgeCalculator into each instance of IPerson so that the IAgeCalculator instance is available to any IPerson that I might later create.

Here is what I have tried so far. It works, but it does not feel right.

static void Main(string[] args) 
{
    IUnityContainer container = new UnityContainer();
    container.RegisterType<IAgeCalculator, AgeInYearsCalculator>("Years");
    container.RegisterType<IAgeCalculator, AgeInDaysCalculator>("Days");

    // Using the initializer like this does not feel right, 
    // but I cant think of another way...

    var ageCalculator = container.Resolve<IAgeCalculator>("Days");
    var personInitializer = new InjectionMethod("Initializer", ageCalculator);
    container.RegisterType<IPerson, Person>(personInitializer);

    var person1 = Factory<IPerson>.Create(container);
    person1.Name = "Jacob";
    person1.Gender = "Male";
    person1.Birthday = new DateTime(1995, 4, 1);

    var person2 = Factory<IPerson>.Create(container);
    person2.Name = "Emily";
    person2.Gender = "Female";
    person2.Birthday = new DateTime(1998, 10, 31);
}

Here are my class definitions:

public interface IAgeCalculator 
{
    string GetAge(IPerson person);
}

internal class AgeInYearsCalculator : IAgeCalculator
{
    public string GetAge(IPerson person) {
        var years = DateTime.Now.Subtract(person.Birthday).TotalDays / 365;
        return years.ToString("0.00") + " years";
    }
}

internal class AgeInDaysCalculator : IAgeCalculator 
{
    public string GetAge(IPerson person) {
        var days = (DateTime.Now.Date - person.Birthday).TotalDays;
        return days.ToString("#,#") + " days";
    }
}

public interface IPerson
{
    string Name { get; set; }
    string Gender { get; set; }
    DateTime Birthday { get; set; }
    string Age { get; }
}

public class Person : IPerson
{
    private IAgeCalculator _ageCalculator;
    public void Initializer(IAgeCalculator ageCalculator) {
        _ageCalculator = ageCalculator;
    }

    public string Name { get; set; }
    public string Gender { get; set; }
    public DateTime Birthday { get; set; }
    public string Age => _ageCalculator.GetAge(this);
}

public class Factory<T> 
{
    public static T Create(IUnityContainer container) {
        return container.Resolve<T>();
    }
}

Is there a better way?

AlfredBr

Register IAgeCalculator using RegisterInstance<T> (not RegisterType<T>) and pass in an instance derived from that type.

static void Main(string[] args)
{
    IUnityContainer container = new UnityContainer();
    container.RegisterInstance<IAgeCalculator>("Years", new AgeInYearsCalculator());
    container.RegisterInstance<IAgeCalculator>("Days", new AgeInDaysCalculator());
    container.RegisterType<IPerson, Person>();

    var person1 = Factory<IPerson>.Create(container);
    person1.Name = "Jacob";
    person1.Gender = "Male";
    person1.Birthday = new DateTime(1995, 4, 1);

    var person2 = Factory<IPerson>.Create(container);
    person2.Name = "Emily";
    person2.Gender = "Female";
    person2.Birthday = new DateTime(1998, 10, 31);
}

Then in your Person class, mark AgeCalculator with the [Dependency] attribute.

public class Person : IPerson
{
    [Dependency("Days")]
    public IAgeCalculator AgeCalculator { get; set; }
    public string Name { get; set; }
    public string Gender { get; set; }
    public DateTime Birthday { get; set; }
    public string Age => AgeCalculator.GetAge(this);
}

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