Question

I have a WPF view that displays a Shipment entity. I have a textblock that contains an asterisk which will alert a user that the record is changed but unsaved. I originally hoped to bind the visibility of this (with converter) to the Shipment.EntityState property.

If value = EntityState.Modified Then
    Return Visibility.Visible
Else
    Return Visibility.Collapsed
End If

The property gets updated just fine, but the view is ignorant of the change. What I need to know is, how can I get the UI to receive notification of the property change. If this cannot be done, is there a good way of writing my own IsDirty property that handles editing retractions (i.e. if I change the value of a property, then change it back to it’s original it does not get counted as an edit, and state remains Unchanged).

Any help, as always, will be greatly appreciated.

Cory

Answer 1

I don’t see a way to create a XAML binding on an existing property to do what you are trying to do. But you could write your own IsDirty property, based on the EntityState; you could update this value by subscribing to the PropertyChanged event raised by the base EntityObject. Of course, you’ll need to also raise a PropertyChanged event for IsDirty (so that the GUI is notified) and ignore this event in your handler (to prevent infinite recursion).
Edit: added the following after question by OP:

This is how I see it, in order to answer the comment.

In the shipment class, one can add:

public bool IsDirty { get { return EntityState == EntityState.Modified; } }

public Shipment() {
...
PropertyChanged += OnShipmentChanged;
}

private void OnShipmentChanged(object sender, PropertyChangedEventArgs pcea) {
    if (pcea.PropertyName != "IsDirty") { // prevent recursion
        OnPropertyChanged("IsDirty"); // notifies binding listener that the state has changed
    }
}

During the night, I thought of another way, which is to create a multi-binding on each Shipment property (which would replace this whole notion of an IsDirty property and would actually answer the original question). This could make sense if there are just a couple of Shipment properties. I’d say if there are more than 3, we should forget about this idea.