Reference of view model locator in MVVM light by using a class

Question

I am trying code bellow to find reference of view model locator but I am getting an error saying object reference can not be set to instance of an object :-

internal class Locator : ViewModelLocator
{
    private static readonly Lazy<Locator> _locator = new Lazy<Locator>(() => new Locator(), LazyThreadSafetyMode.PublicationOnly);
    public static Locator Instance => _locator.Value;
    private Locator()
    {
        SimpleIoc.Default.Register<MainViewModel>();
        SimpleIoc.Default.Register<AddStudentViewModel>();
    }
 }

Can any one help me in that, To solve this?

Answer 1

you need to create method like this after registering your viewmodel

    public CreateAssetViewModel CreateAssetVM
    {
        get
        {
            if (!SimpleIoc.Default.IsRegistered<CreateAssetViewModel>())
            {
                SimpleIoc.Default.Register<CreateAssetViewModel>();
            }
            return ServiceLocator.Current.GetInstance<CreateAssetViewModel>();
        }
    }

Answer 2

I am using bellow code in my project, you need to add public get set property for locating your view model in the locator class:-

 internal class Locator : ViewModelLocator
        {
            private static readonly Lazy<Locator> _locator = new Lazy<Locator>(() => new Locator(), LazyThreadSafetyMode.PublicationOnly);
            public static Locator Instance => _locator.Value;

            private Locator()
            {
                SimpleIoc.Default.Register<MainViewModel>();
                SimpleIoc.Default.Register<AddStudentViewModel>();

            }

            public MainViewModel Main
            {
                get
                {
                    return ServiceLocator.Current.GetInstance<MainViewModel>();
                }
            }
            public AddStudentViewModel AddStudentViewModel
            {
                get
                {
                    return ServiceLocator.Current.GetInstance<QuestionsViewModel>();
                }
            }

        } 

or else another way of implementing the same is as bellow :- you can create a get set property of locator in app.cs :-

 public static ViewModelLocator Locator
        {
            get { return _locator ?? new ViewModelLocator(); }
        }

Answer 3

I would prefer you first method by lazy loading you can find reference of your locator :)

private static readonly Lazy<Locator> _locator = new Lazy<Locator>(() => new Locator(), LazyThreadSafetyMode.PublicationOnly);
            public static Locator Instance => _locator.Value;