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.

According to the author of MVVMLight, it is possible: http://stackoverflow.com/questions/7297014/does-the-mvvm-light-simpleioc-support-singletons — Fayilt, Jan 30 '14 at 13:04

score 1 · Accepted Answer · edited May 23 '17 at 11:51

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));
}

To build the business object I cannot use the default parameterless constructor, I need to pass certain values, in certain cases complex business objects themselves. Thus, I cannot just register a class name for the container. It needs to be my very object, or I need to pass parameters somehow in class registration. — Eugene Bykov, Jan 31 '14 at 05:52
Thank you! Your update helped me to achieve exactly what I was looking for! — Eugene Bykov, Jan 31 '14 at 12:50

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

1 Answers1