MVVM中子属性的PropertyChanged

Question

I'm struggling a little with the structure of my project still, and ran into an issue which im worried demonstrates that i'm still missing a good understanding of the right way to do things.

What i have currently is:

The program displays information for shipping, this is based on an overall project which contains proformas which contains shipments which contains containers (this is simplified for this example)

So in order to keep track of the currently selected objects (Project, proforma etc.) i have a class called ProjectTree which looks similar to this:

Public class ProjectTree
{
  Public Project SelectedProject { get; set; }
  Public Proforma SelectedProforma { get; set; }
  public Shipment SelectedShipment { get; set; }
}

again this is simplified, now since Project itself contains the list of Proformas, i have a function on Project called LoadProformas() which creates a new thread and loads that projects proformas into an ObservableCollection within project itself (the loading is done by a set of IManagers that handle all the data loading, saving etc. )

Now the issue i'm faced with is that say my viewmodel ProformaListViewModel has access to ProjectTree so it can call the LoadProformas() on the Project, i run into the issue of databinding the _ProjectTree.SelectedProject.ProformaList as i wont know when the data has actually been loaded since (afaik) NotifyOfPropertyChange wont flow through into the viewmodel in this scenario. Now i could always use the EventAggregator and fire an event when the data is loaded (and this is what I've done in the past) however whenever i look at this it seem a bit... haphazard, to be firing unbound events from an child object to the parent.

Have i missed something critical in my understanding here? Or would using the event be a reasonable way to accomplish what i need?

EDIT:

Just to clear this up, the reason im trying to do this is because each project has a list of proformas and each proforma a list of shipments etc. Originally the managers handled the lists of objects as well as loading and saving, but i found that having them totally uncoupled what causing issue when trying to do work with a project based on its shipments (for example)

Answer 1

In my opinion, you shouldn't be using any Selected... properties in your data type/model classes... those properties belong in your view model classes. Furthermore, unless you actually use an object in your work that is called a ProjectTree , I wouldn't name your object that... just stick to real world names.

Also, I'd advise against putting functionality in your data type classes... in my opinion (for the most part) they should just be containers for data. I would structure the view model like this (I'm ignoring the INotifyPropertyChanged interface in this example, but you'll need to correctly implement it):

public class ProjectViewModel : INotifyPropertyChanged
{
    public ObservableCollection<Project> Projects { get; set; }
    public Project SelectedProject { get; set; }
    public ObservableCollection<Proforma> Proformas { get; set; }
    public Proforma SelectedProforma { get; set; }
    public ObservableCollection<Shipment> Shipments { get; set; }
    public Shipment SelectedShipment { get; set; }

    public void LoadProjects() {}
    public void LoadProformas() {}             
    public void LoadShipments() {}             
}

Next, you mentioned that you're using the EventAggregator instead of the INotifyPropertyChanged interface... it seems to me that you are making your life more difficult than it needs to be as the INotifyPropertyChanged interface can be used for this just fine. Implement it in both your data type classes and your view model classes and then it will work for every property. Remember, you can add a PropertyChanged handler in your view model(s) too.

Answer 2

did you try to call manually to

PropertyChanged(this, new PropertyChangedEventArgs("ProformaList"));

after loading the projects proformas ?

Answer 3

Each of your viewModel classes (your Project, Proforma, and shipment classes may in this case be acting as both the model and viewModel) need to implement the INotifyPropertyChanged interface. Then your view should databind directly to the property SelectedProject.ProformaList . Since the list is an ObservableCollection already, your view will be notified when items are added or removed. You then just need to ensure that the PropertyChanged notification is raised when the ProformaList property itself is changed.

Since every property that is bound in the View should Notify of Property Changes, each level of your data 'tree' (Project, Proforma, Shipment) can be changed independently and still update the view.