Question

I have a usercontrol bound to a VM. This VM contains a collection property, lets call it “MyCollection” and several regular properties lets call one of them “SomeProperty”. As you can see, the get and set logic for this property references the collection in the VM.

The problem is, when I make a change to “MyCollection”, this obviously has an impact on the values that are shown in the UI (as they are calculated based on it). However, my UI doesn’t appear to be smart enough to update itself whenever “MyCollection” changes.

Here is the VM my usercontrol is bound to:

public class MyVM
{
    private ObservableCollection<SomeOtherVM> _myCollection = new ObservableCollection<SomeOtherVM>();

    public MyVM()
    {

    }

    public ObservableCollection<SomeOtherVM> MyCollection
    {
        get { return _myCollection; }
        [Notify]
        set 
        { 
            _myCollection = value;
        }
    }

    public virtual string SomeProperty
    {
        get
        {
            if (_myCollection.Count == 1)
                return _myCollection[0].SomeProperty;
            else
                return "More than one "SomeOtherVM" has been selected";
        }
        [Notify]
        set
        {
            foreach (SomeOtherVM s in _myCollection)
            {
                s.SomeProperty = value;
            }
        }
    }
}

}

Note that nothing in my usercontrol is directly bound to the collection, it is only bound to other properties that reference the collection in its get; set; methods.

Is there anything I could do in the VM to force the UI to update whenever “MyCollection” is changed? I want to avoid having to put anything in the code behind for the user control.

Answer 1

Subscribe to CollectionChanged of MyCollection and fire PropertyChanged-notifications for the other properties there (no fancy attribute usage for you).