How to Override PropertyChangedCallback of a predefined Dependency Property ItemsSource in a WPF ItemsControl

Question

How to Override PropertyChangedCallback of a predefined Dependency Property ItemsSource in a WPF ItemsControl.

I developed a WPF Custom Control inherited from ItemsControl. In that I used the predefined Dependency Property ItemsSource. In that I need to monitor and check data once the Collection gets updated.

I searched a lot in google, but I can't able to find any related solution to fulfill my requirement.

https://msdn.microsoft.com/en-us/library/system.windows.controls.itemscontrol.itemssource(v=vs.110).aspx

Kindly assist me, whats the method name to Override ?...

Answer 1

Call OverrideMetadata in a static constructor of your derived ItemsSource class:

public class MyItemsControl : ItemsControl
{
    static MyItemsControl()
    {
        ItemsSourceProperty.OverrideMetadata(
            typeof(MyItemsControl),
            new FrameworkPropertyMetadata(OnItemsSourcePropertyChanged));
    }

    private static void OnItemsSourcePropertyChanged(
        DependencyObject obj, DependencyPropertyChangedEventArgs e)
    {
        ((MyItemsControl)obj).OnItemsSourcePropertyChanged(e);
    }

    private void OnItemsSourcePropertyChanged(DependencyPropertyChangedEventArgs e)
    {
        var oldCollectionChanged = e.OldValue as INotifyCollectionChanged;
        var newCollectionChanged = e.NewValue as INotifyCollectionChanged;

        if (oldCollectionChanged != null)
        {
            oldCollectionChanged.CollectionChanged -= OnItemsSourceCollectionChanged;
        }

        if (newCollectionChanged != null)
        {
            newCollectionChanged.CollectionChanged += OnItemsSourceCollectionChanged;
            // in addition to adding a CollectionChanged handler
            // any already existing collection elements should be processed here
        }
    }

    private void OnItemsSourceCollectionChanged(
        object sender, NotifyCollectionChangedEventArgs e)
    {
        // handle collection changes here
    }
}