Why ObservableCollection is not updated on items change?

Question

I noticed that ObservableCollection in WPF reflects changes in GUI only by adding or removing an item in the list, but not by editing it.

That means that I have to write my custom class MyObservableCollection instead. What is the reason for this behaviour?

Thanks

Answer 1

The ObservableCollection has no way of knowing if you make changes to the objects it contains - if you want to be notified when those objects change then you have to make those objects observable as well (for example by having those objects implement INotifyPropertyChanged)

Answer 2

another way of achieving this would be that you implement a new XXXViewModel class that derives from DependencyObject and you put this one in the ObservableCollection.

for this look at this very good MVVM introduction: http://blog.lab49.com/archives/2650

an example for such a class would be:

public class EntryViewModel : DependencyObject
{
    private Entry _entry;
    public EntryViewModel(Entry e)
    {
        _entry = e;
        SetProperties(e);
    }

    private void SetProperties(Entry value)
    {

        this.Id = value.Id;
        this.Title = value.Title;
        this.CreationTimestamp = value.CreationTimestamp;
        this.LastUpdateTimestamp = value.LastUpdateTimestamp;
        this.Flag = value.Flag;
        this.Body = value.Body;
    }


    public Entry Entry
    {
        get {
            SyncBackProperties();
            return this._entry;
        }
    }


    public Int64 Id
    {
        get { return (Int64)GetValue(IdProperty); }
        set { SetValue(IdProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Id.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty IdProperty =
        DependencyProperty.Register("Id", typeof(Int64), typeof(EntryViewModel), new UIPropertyMetadata(new Int64()));

}}

important things here: - it derives from DependencyObject - it operates with DependencyProperties to support WPFs databinding

br sargola