fix popup not displaying in correct place if a control expands

Author: ButchersBoy

MainDemo.Wpf/Trees.xaml

@@ -112,12 +112,11 @@
             </TreeView>
             <materialDesign:PopupBox Grid.Row="1"
                                      Style="{StaticResource MaterialDesignMultiFloatingActionPopupBox}"
-                                     PlacementMode="LeftAndAlignTopEdges"
-                                     ToolTipService.Placement="Bottom"
+                                     PlacementMode="LeftAndAlignMiddles"                                     
                                      ToolTip="Manage items"
                                      Margin="0 0 10 10"
                                      HorizontalAlignment="Right" VerticalAlignment="Bottom">
-                <StackPanel>
+                <StackPanel Orientation="Horizontal">
                     <Button ToolTip="Add an item"
                             Command="{Binding AddCommand}">
                         <Path Data="M19,13H13V19H11V13H5V11H11V5H13V11H19V13Z"

MaterialDesignThemes.Wpf/PopupBox.cs

@@ -242,7 +242,9 @@ private static void IsPopupOpenPropertyChangedCallback(DependencyObject dependen
             }
 
             if (newValue)            
-                popupBox.AnimateChildren();            
+                popupBox.AnimateChildren();          
+            
+            popupBox._popup?.RefreshPosition();
 
             VisualStateManager.GoToState(popupBox, newValue ? PopupIsOpenStateName : PopupIsClosedStateName, true);
         }