public static ViewModelChangePropagation <T> Observe <T>(
this ViewModelChangePropagation <T> self,
PropertyChangedEventHandler callback) where T : INotifyPropertyChanged
{
if (self.Change.Changed)
{
if (self.Change.OldValue != null)
{
self.Change.OldValue.PropertyChanged -= callback;
}
if (self.Change.NewValue != null)
{
self.Change.NewValue.PropertyChanged += callback;
}
}
return(self);
}
public static ViewModelChangePropagation <IReadOnlyCollection <T> > ObserveChildren <T>(
this ViewModelChangePropagation <IReadOnlyCollection <T> > self,
PropertyChangedEventHandler callback) where T : INotifyPropertyChanged
{
if (self.Change.Changed)
{
var removedChildren = self.Change.OldValue.Except(self.Change.NewValue);
var addedChildren = self.Change.NewValue.Except(self.Change.OldValue);
foreach (var child in removedChildren)
{
child.PropertyChanged -= callback;
}
foreach (var child in addedChildren)
{
child.PropertyChanged += callback;
}
}
return(self);
}
