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I got a question about how can I use a common ObservableCollection in two ViewModels in WPF C#?

I got two views, first view consist of a a observablecollection of categories used in a combobox in some form. The second view is a window which enable adding, editing and removal of categories. Now I'm retrieving the categories for both views separately, but I want to combine and use a common observable collection, in order to get the new changes when I added, change or remove categories in the second view.

Both Views and viewmodels is controlled by a mainviewmodel:

    public viewModel1 viewModel1 { get; set; }

    public ViewModel2 ViewModel2 { get; set; }



    public MainViewModel()

    {

        this.InitializeCommands();

        this.viewModel1 = new viewModel1();

        this.ViewModel2 = new ViewModel2();





        this.ViewModel2.OnChangedCategory += (s, e) =>

        {

            this.viewModel1.Categories = GetCategories();

        };

    }

ViewModel for View1:

public ObservableCollection<Categories> GetCategories

    {

        get

        {

            if (this._getCategories == null)

            {

                this._getCategories = methods.GetCategories();

            }



            return this._getCategories ;

        }

        set

        {

            if (this._getCategories != value)

            {

                this._getCategories = value;

                this.OnPropertyChanged("GetCategories");

            }

        }

    }

ViewModel for View2:

public ObservableCollection<Categories> GetCategories

    {

        get

        {

            if (this._getCategories == null)

            {

                this._getCategories = methods.GetCategories();

            }



            return this._getCategories ;

        }

        set

        {

            if (this._getCategories != value)

            {

                this._getCategories = value;

                this.OnPropertyChanged("GetCategories");

            }

        }

    }

In theory, they are both identical, just two different observable collection in two viewmodels, I want to use the same observable collection in both views, if it's in the first or second ViewModel doesn't matter. But it makes maybe more sense if it's in viewmodel 2. Let's say if I decide have a common categories observable collection in ViewModel 2, how can Viewmodel 1 use this observable collection from ViewModel 2 and still be in sync upon changes?

How can I do this?

You could make it a resource and then any code could get at it.
The sample associated with this article has two pairs of usercontrols share two such collections and sounds fairly similar to your requirement.

https://social.technet.microsoft.com/wiki/contents/articles/29859.wpf-tips-bind-to-current-item-of-collection.aspx