Change Notification in MVVM Hierarchies

Question

Let\'s say in some abstract ViewModel base-class I have a plain-old property as follows:

public Size Size
{
    get { return _size; }
    set
    {
        _size         


        

Answer 1

You can simply override OnPropertyChanged in the derived ViewModel like so:

protected override void OnPropertyChanged(string propertyName) {
    base.OnPropertyChanged(propertyName);
    if (propertyName == "Size") {
        base.OnPropertyChanged("Rectangle");
    }
}

Another possibility... A while back I put together a pretty nice ViewModel base class that supports attributes on properties like:

[DependsOn("Size")]
public Rect Rectangle {
    get { new Rect(0,0,Size.Width, Size.Height); }
}

Then the ViewModel base class collects these DependsOnAttribute's at runtime and in its OnPropertyChanged method it basically just looks to see what other properties need to be invalidated when a property change occurs.