support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Tools/Extension/UIElementExtension.cs

@@ -0,0 +1,45 @@
+using System.Windows;
+
+namespace HandyControl.Tools.Extension
+{
+    // ReSharper disable once InconsistentNaming
+    public static class UIElementExtension
+    {
+        /// <summary>
+        ///     显示元素
+        /// </summary>
+        /// <param name="element"></param>
+        public static void Show(this UIElement element)
+        {
+            element.Visibility = Visibility.Visible;
+        }
+
+        /// <summary>
+        ///     显示元素
+        /// </summary>
+        /// <param name="element"></param>
+        /// <param name="show"></param>
+        public static void Show(this UIElement element, bool show)
+        {
+            element.Visibility = show ? Visibility.Visible : Visibility.Collapsed;
+        }
+
+        /// <summary>
+        ///     不现实元素，但保留空间
+        /// </summary>
+        /// <param name="element"></param>
+        public static void Hide(this UIElement element)
+        {
+            element.Visibility = Visibility.Hidden;
+        }
+
+        /// <summary>
+        ///     不显示元素，且不保留空间
+        /// </summary>
+        /// <param name="element"></param>
+        public static void Collapse(this UIElement element)
+        {
+            element.Visibility = Visibility.Collapsed;
+        }
+    }
+}