Virgo_Mask/Framework/Common/StylableWindow/WindowDragBehavior.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;

namespace WpfStyleableWindow.StyleableWindow
{
    public static class WindowDragBehavior
    {
        public static Window GetLeftMouseButtonDrag(DependencyObject obj)
        {
            return (Window)obj.GetValue(LeftMouseButtonDrag);
        }

        public static void SetLeftMouseButtonDrag(DependencyObject obj, Window window)
        {
            obj.SetValue(LeftMouseButtonDrag, window);
        }

        public static readonly DependencyProperty LeftMouseButtonDrag = DependencyProperty.RegisterAttached("LeftMouseButtonDrag",          
            typeof(Window), typeof(WindowDragBehavior),
            new UIPropertyMetadata(null, OnLeftMouseButtonDragChanged));

        private static void OnLeftMouseButtonDragChanged(object sender, DependencyPropertyChangedEventArgs e)
        {
            var element = sender as UIElement;

            if (element != null)
            {         
                element.MouseLeftButtonDown += buttonDown;
                
            }
        }        

        private static void buttonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            var element = sender as UIElement;

            var targetWindow = element.GetValue(LeftMouseButtonDrag) as Window;

            if (targetWindow != null)
            {
                targetWindow.DragMove();
            }
        }
    }
}