What does "FreshIOC.Container.Register" do?

Question

I am doing a course of MVVM for Xamarin Forms, and the teacher in one class used FreshIOC.Container.Register to "register different instances or dependencies", and I don't understand how that affects my code, if someone can explain it I would appreciate it.

My code as an example:

public App()
{
    InitializeComponent();

    FreshIOC.Container.Register<IContactService,ContactService>();
    FreshIOC.Container.Register<IUserDialogs>(UserDialogs.Instance);
}

class MainViewModel : FreshBasePageModel
    {
        private IContactService service;
        private IUserDialogs dialog;
        public MainViewModel(IContactService Service, IUserDialogs Dialog)
        {
            service = Service;
            dialog = Dialog;
        }

        public override async void Init(object initData)
        {
            dialog.ShowLoading();
            var tempt = await service.GetData();
            Contacts = tempt;
            dialog.HideLoading();
        }  
    }

I don't see what FreshIOC.Container.Register does, or how it connects to the MainViewModel class. By the way, there is another method called "Resolve" instead of "Register", If you could also explain that one I would appreciate it.

That is all, if you need anything more from my code I will provide it as soon as I see your request, thank you all so much for your time, have a nice day.

Answer 1

The Register registers your concrete classes at the IoC framework.

So, IoC in short will work like this:

Instead of making new ContactService all the time, you'll ask the IoC framework to give you one.

This has some benifits;

• because you often register by interface, you only need to worry about the ContractService constructor at one place, and not all over the place.
• it makes your code better testable because the consuming page is not responsible for creating the service. This might sound a bit mystic, but if you write unit test, you'll immediate see the benefits.

what does Register do?

It makes sure you can request this service from the IoC framework.

The first one registers the ContactService as an IContactService; so, if you request an IContactService you'll get the registered type.

The second one registers the instance of a type: if you request it, you'll always get that instance. Works well for settings and thread safe stuff. Works not at all for database related things.

What does Resolve do?

It enables you to retrieve a service from the IoC framework, but note: there might be better ways e.g. by constructor injection.

---

This code is an example of constructor injection: by registering the IContactService you've enabled the possibility to resolve the service automatically. If you ommit the registration this is not possible:

public MainViewModel(IContactService Service, IUserDialogs Dialog)
{
   service = Service;
   dialog = Dialog;
}

---

If you didnt use the IoC framework, you would have ended up with new ContactService in every model you where using, which can be considered as an antipattern for such services, because;

• changing the implementation concrete type will result in a lot of code changes.
• changing the constructor would lead to a lot of code changes
• unittesting the consumer causes an instantation of the service, which can lead to side effects.