[NUI] Add Comment on the View.VisibilityChanged event

Signed-off-by: seungho baek <sbsh.baek@samsung.com>

diff --git a/src/Tizen.NUI/src/public/BaseComponents/ViewEvent.cs b/src/Tizen.NUI/src/public/BaseComponents/ViewEvent.cs
index 97a4615..eb0a781 100755 (executable)
--- a/src/Tizen.NUI/src/public/BaseComponents/ViewEvent.cs
+++ b/src/Tizen.NUI/src/public/BaseComponents/ViewEvent.cs
@@ -414,11 +414,21 @@ namespace Tizen.NUI.BaseComponents
                 }
             }
         }
-
         /// <summary>
         /// An event for visibility change which can be used to subscribe or unsubscribe the event handler.<br />
-        /// This signal is emitted when the visible property of this or a parent view is changed.<br />
+        /// This event is sent when the visibility of this or a parent view is changed.<br />
         /// </summary>
+        /// <remarks>
+        /// <para>
+        /// When VisibilityChangedEventArgs.Type is SELF, VisibilityChangedEventArgs.Visibility is true means this View's Visibility property is true.
+        /// When VisibilityChangedEventArgs.Type is PARENT, VisibilityChangedEventArgs.Visibility is true means a parent's Visibility property has changed to true.
+        /// </para>
+        /// <para>
+        /// This event is NOT sent if the view becomes transparent (or the reverse), it's ONLY linked with View.Show() and View.Hide().
+        /// For reference, a view is only shown if the view and its parents (up to the root view) are also visible, they are not transparent, and the view has a non-zero size.
+        /// So if its parent is not visible, the view is not shown even though VisibilityChangedEventArgs.Type is SELF and VisibilityChangedEventArgs.Visibility is true.
+        /// </para>
+        /// </remarks>
         /// <since_tizen> 3 </since_tizen>
         public event EventHandler<VisibilityChangedEventArgs> VisibilityChanged
         {