WPF 依赖附加属性

附加属性的本质是一个依赖属性，与普通的依赖属性区别：

1：注册方法名不一样，如 DependencyProperty.RegisterAttached

2：没有普通的属性包装器，而是通过get和set属性来实现属性包装

3：没有普通的.NET属性

public static readonly DependencyProperty KeepAliveProperty =  DependencyProperty.Register(
"KeepAlive",
 typeof(bool),
 typeof(Window),
 new PropertyMetadata(KeepAliveChanged));

        /// <summary>
        /// 获取一个值，该值指示是否在现代化框架实例中保持指定对象的活动状态/// </summary>
        /// <param name="o">The target dependency object.</param>
        /// <returns>Whether to keep the object alive. Null to leave the decision to the ModernFrame.</returns>
        public static bool? GetKeepAlive(DependencyObject o)
        {
            if (o == null) {
                throw new ArgumentNullException("o");
            }
            return (bool?)o.GetValue(KeepAliveProperty);
        }

        /// <summary>
        /// 设置一个值，该值指示是否在现代化框架实例中保持指定对象的活动状态/// </summary>
        /// <param name="o">The target dependency object.</param>
        /// <param name="value">Whether to keep the object alive. Null to leave the decision to the ModernFrame.</param>
        public static void SetKeepAlive(DependencyObject o, bool? value)
        {
            if (o == null) {
                throw new ArgumentNullException("o");
            }
            o.SetValue(KeepAliveProperty, value);
        }

        private static void KeepAliveChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var window = d as Window;
            if (window != null)
            {
                window.DialogResult = e.NewValue as bool?;
            }
        }

用法：