How to persist a single business object with MVVM-Light SimpleIoc

Question

I have a complex business object, which I create at user login, and need to persist it throughout most viewmodels of the application. What I can do is send it with the messenger each time I create a new viewmodel, that works, but it's too much code, which is all the same every time, and I believe it is not a correct way of doing things. What I did in windows forms - I had all forms inherit from a base class, that has this business object as a member, and is included in constructor. I believe, SimpleIoc may be used for the problem. Well, here how to use MVVMLight SimpleIoc? I've fouond an indication that a concrete object may be registered (but for the interface - why?). So, is there a way to store an object in the container throughout the lifetime of an application? And it has parameters in constructor if this is important.

Answer 1

As it states in the linked tutorial

2) Every object is a singleton by default. To resolve an object so that it's not a singleton you need to pass a unique value to the GetInstance call:

SimpleIoc.Default.GetInstance<MainViewModel>(Guid.NewGuid().ToString());

So to get the same instance each time you pass nothing (or always the same value) to the call to GetInstance

[Test]
public void CreateNonGeneric_ReturnsSameInstance1()
{
    SimpleIoc.Default.Register<Repository>();

    var result1 = SimpleIoc.Default.GetInstance<Repository>();
    var result2 = SimpleIoc.Default.GetInstance<Repository>();

    Assert.That(result1, Is.SameAs(result2));
}

[Test]
public void CreateNonGeneric_ReturnsSameInstance2()
{
    SimpleIoc.Default.Register<IRepository, Repository>();

    var result1 = SimpleIoc.Default.GetInstance<IRepository>();
    var result2 = SimpleIoc.Default.GetInstance<IRepository>();

    Assert.That(result1, Is.SameAs(result2));
}

[Test]
public void CreateNonGeneric_ReturnsSameInstance3()
{
    SimpleIoc.Default.Register<Repository>();

    var result1 = SimpleIoc.Default.GetInstance<Repository>("alwaysthesame");
    var result2 = SimpleIoc.Default.GetInstance<Repository>("alwaysthesame");

    Assert.That(result1, Is.SameAs(result2));
}

---

UPDATE

You can configure the dependencies during the registration. Here's one with a string

[Test]
public void RegisterSingletonWithFunc_GetIstance_ReturnsSameInstanceEachTime()
{
    SimpleIoc.Default.Register<IRepository, Repository>();
    SimpleIoc.Default.Register<Repository>(() => 
        new Repository("dependency"), "single");
    var result1 = SimpleIoc.Default.GetInstance<IRepository>("single");
    var result2 = SimpleIoc.Default.GetInstance<IRepository>("single");

    Assert.That(result1, Is.SameAs(result2));
}

And here's one with a dependency that is created by SimpleIoc

[Test]
public void RegisterSingletonWithDependentClass_GetIstance_ReturnsSame()
{
    SimpleIoc.Default.Register<IRepository, Repository>();
    SimpleIoc.Default.Register<SomeService>();
    SimpleIoc.Default.Register<Repository>(() => 
        new Repository(
            SimpleIoc.Default.GetInstance<SomeService>())
            , "single");
    var result1 = SimpleIoc.Default.GetInstance<IRepository>("single");
    var result2 = SimpleIoc.Default.GetInstance<IRepository>("single");

    Assert.That(result1, Is.SameAs(result2));
}