C# WPF MVVM - View doesn't change when Item Added to ObservableCollection in VM Instance

Question

Description

I am currently building an app where if the user triggers an event on a combobox found on the Main View, it will take the selecteditem and add it to a ObservableCollection on a secondary view, when the user triggers the event to add the item, it successfully adds it to the Collection but does not update the UI in the ItemsControl that the ObservableCollection is a binding of.

Problem

UI isn't updating when ObservableCollection has an item added to it in another ViewModel.

JobList

JobList is derived from the ObservableCollection type allowing for the loading of later stored data using xml on loading the application, it has a limit of 6 items.

class JobList : ObservableCollection
{
    public JobList () : base ()
    {
        if (JobListExists)
            LoadExistingJobList();
    }

    private bool JobListExists
    {
        get {

            bool result = false;

            if (File.Exists(recentsPath + @"\RecentItems.xml"))
            {
                result = true;
            }

            return result;
        }
    }

    private void LoadExistingJobList ()
    {
        using (var reader = new StreamReader(recentsPath + @"\RecentItems.xml"))
        {
            XmlSerializer deserializer = new XmlSerializer(typeof(List),
                new XmlRootAttribute("Jobs"));
            List jobs = (List)deserializer.Deserialize(reader);

            foreach (Job job in jobs)
            {
                Add(job);
            }
        }
    }

    public void AddToCollection (Job job)
    {
        Insert(0, job);

        if (Count == 7)
            RemoveAt(6);
    }
}

MainView

The MainView is being used for the MainWindow and stores the SearchBox (To be used in multiple places) and a ContentControl that stores the CurrentView. When an event occurs from here, no subsequent changes happen to the view bound to the ContentControl.

MainViewModel

class MainViewModel : ObservableObject
{
    public RelayCommand HomeViewCommand { get; set; }
    public RelayCommand GlobalViewCommand { get; set; }
    public RelayCommand SearchBoxCommand { get; set; }

    public HomeViewModel HomeVM { get; set; }
    public GlobalViewModel GlobalVM { get; set; }

    private object _currentView;

    public object CurrentView
    {
        get { return _currentView; }
        set
        {
            _currentView = value;
            OnPropertyChanged();
        }
    }

    private ICollectionView _currentDropdownData;

    public ICollectionView CurrentDropdownData
    { 
        get { return _currentDropdownData; }
        set
        {
            _currentDropdownData = value;
            OnPropertyChanged("CurrentDropdownData");
        }
    }

    public MainViewModel()
    {
        CurrentDropdownData = CollectionViewSource.GetDefaultView(DataProvider.GetProjectItems());
        HomeVM = new HomeViewModel();
        GlobalVM = new GlobalViewModel();
        CurrentView = HomeVM;

        HomeViewCommand = new RelayCommand(o =>
        {
            CurrentDropdownData = CollectionViewSource.GetDefaultView(DataProvider.GetProjectItems());
            CurrentView = HomeVM;
            SearchBoxCommand = new RelayCommand(e =>
            {
                ((HomeViewModel)CurrentView).Collection.AddToCollection((Job)CurrentDropdownData.CurrentItem);
            });
        });

        GlobalViewCommand = new RelayCommand(o =>
        {
            CurrentDropdownData = CollectionViewSource.GetDefaultView(DataProvider.GetGlobalItems());
            CurrentView = GlobalVM;
            SearchBoxCommand = new RelayCommand(e =>
            {
            });
        });

        SearchBoxCommand = new RelayCommand(e =>
        {
            ((HomeViewModel)CurrentView).Collection.AddToCollection((Job)CurrentDropdownData.CurrentItem);
        });
    }
}

HomeView

The Home View solely uses a ItemsControl that refers to the "Collections" JobList as a DataBinding to display the currently selected Jobs

HomeViewModel

The HomeViewModel very simply stores the Collection that is being used in the View for databinding.

class HomeViewModel : ObservableObject
{
    private JobList _collection;

    public JobList Collection
    {
        get { return _collection; }
        set
        {
            _collection = value;
            OnPropertyChanged("Collection");
        }
    }

    public HomeViewModel ()
    {
        Collection = new JobList()
        {
            new Job () { Name = "Test" },
            new Job () { Name = "Test 2" },
            new Job () { Name = "Test 3" }
        };
    }
}

EldHasp · Accepted Answer

There can be only one reason.
You have different instances of HomeViewModel in Window and UserControl.
The UserControl does not have to create its own Data Context.
He should get it from the Window by binding to the CurrentView.

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