DropDownButton: fixed issue with initial command not calling CanExecute to check the state of the buttons

ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/DropDownButton/Implementation/DropDownButton.cs

@@ -153,6 +153,15 @@ namespace Microsoft.Windows.Controls
         }
 
         void CanExecuteChanged(object sender, EventArgs e)
+        {
+            CanExecuteChanged();
+        }
+
+        #endregion //Event Handlers
+
+        #region Methods
+
+        private void CanExecuteChanged()
         {
             if (Command != null)
             {
@@ -167,10 +176,6 @@ namespace Microsoft.Windows.Controls
             }
         }
 
-        #endregion //Event Handlers
-
-        #region Methods
-
         /// <summary>
         /// Closes the drop down.
         /// </summary>
@@ -267,6 +272,8 @@ namespace Microsoft.Windows.Controls
                 UnhookCommand(oldValue, newValue);
 
             HookUpCommand(oldValue, newValue);
+
+            CanExecuteChanged(); //may need to call this when changing the command parameter or target.
         }
 
         #endregion //Command