Loading custom control

loadingcontrol.cs

public class LoadingControl : UserControl
    {
        public static readonly DependencyProperty TaskHandlerProperty =
            DependencyProperty.Register(nameof(TaskHandler), typeof(ITaskHandler), typeof(Loading), 
                new FrameworkPropertyMetadata(""));

        public Loading()
        {
            InitializeComponent();
        }

        public ITaskHandler TaskHandler
        {
            get => (ITaskHandler)GetValue(TaskHandlerProperty);
            set => SetValue(TaskHandlerProperty, value);
        }

        private static void OnHandlerChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            // TODO; Register listeners on the new TaskHandler dependencyproperty
            //     bool ITaskHandler.IsBusy will indicate if there is work performing in the background or not
        }

        private void OnTaskBusyChanged(object sender, PropertyChangedEventArgs e) { 
          // TODO; Switch the visibility of the current control:
          //       Visible on IsBusy == true
          //       Collapsed on IsBusy == false
        }
    }

loadingcontrol.xaml

<usercontrol>
  <Border height="50pt">
    <TextBlock Text="Loading.."/>
    </border>
</usercontrol>

shell.xaml

<usercontrol>
  <grid>
    [CONTENTS]
    <loadingcontrol verticalalignment="bottom" TaskHandler="{Binding}"/>
  </grid>
</usercontrol>