Plane.Libraries/Plane.Windows/Controls/ProgressButton.cs

using System.Windows;
using System.Windows.Controls;

namespace Plane.Windows.Controls
{
    public class ProgressButton : Button
    {
        // Using a DependencyProperty as the backing store for IsProcessing.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty IsProcessingProperty =
            DependencyProperty.Register(
                "IsProcessing",
                typeof(bool),
                typeof(ProgressButton),
                new PropertyMetadata(defaultValue: false)
            );

        public bool IsProcessing
        {
            get { return (bool)GetValue(IsProcessingProperty); }
            set { SetValue(IsProcessingProperty, value); }
        }
    }
}