PropertyChangedCallback

Listening to changes on DependencyProperties in WPF can be complex. When you register a DependencyProperty you can supply a static PropertyChangedCallback but if you want to listen to changes from elsewhere things can get complicated and error-prone.

In Avalonia, there is no PropertyChangedCallback at the time of registration, instead a class listener is added to the control's static constructor in much the same way that event class listeners are added.

As side effect of this change, you may need to dispatch events yourself. WPF

treeView.SelectedItemChanged += TreeView_SelectedItemChanged;

// ...

private void TreeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
    var item = treeView.SelectedItem;
    // work with selected item.
}

Avalonia

treeView.PropertyChanged += TreeView_SelectedItemChanged;

// ...

private void TreeView_SelectedItemChanged(object sender, AvaloniaPropertyChangedEventArgs e)
{
    if (e.Property != TreeView.SelectedItemProperty) return;

    var item = treeView.SelectedItem;
    // work with selected item.
}

Even plain text box should be handled in same way. WPF

searchTextBox.TextChanged += new TextChangedEventHandler(searchTextBox_TextChanged);

private void searchTextBox_TextChanged(object sender, TextChangedEventArgs e)
{
    // handle text change
}

Avalonia

searchTextBox.PropertyChanged += searchTextBox_TextChanged;

// ...

private void searchTextBox_TextChanged(object sender, AvaloniaPropertyChangedEventArgs e)
{
    if (e.Property != TextBox.TextProperty) return;

    // handle text change
}