Merge pull request #44 from scdmitryvodich/LayoutFloatingWindowContro…

…lVisibilityProblem

Fix Visibility issue on closing LayoutFloatingWindowControl

source/Components/Xceed.Wpf.AvalonDock/Controls/LayoutFloatingWindowControl.cs

@@ -15,6 +15,7 @@ This program is provided to you under the terms of the Microsoft Public
   ***********************************************************************************/
 
 using System;
+using System.ComponentModel;
 using System.Linq;
 using System.Windows;
 using System.Runtime.InteropServices;
@@ -58,6 +59,7 @@ protected LayoutFloatingWindowControl( ILayoutElement model )
     {
       this.Loaded += new RoutedEventHandler( OnLoaded );
       this.Unloaded += new RoutedEventHandler( OnUnloaded );
+      Closing += OnClosing;
       _model = model;
     }
 
@@ -453,6 +455,19 @@ private void OnUnloaded( object sender, RoutedEventArgs e )
       }
     }
 
+    private void OnClosing(object sender, CancelEventArgs e)
+    {
+      Closing -= OnClosing;
+
+      // If this window was Closed not from InternalClose method,
+      // mark it as closing to avoid "InvalidOperationException: : Cannot set Visibility to Visible or call Show, ShowDialog,
+      // Close, or WindowInteropHelper.EnsureHandle while a Window is closing".
+      if (!_isClosing)
+      {
+        _isClosing = true;
+      }
+    }
+
     private void OnActivated( object sender, EventArgs e )
     {
       this.Activated -= new EventHandler( OnActivated );