Merge pull request #3878 from vgromfeld/wrapPanelCollapsedItems

Fix WrapPanel behavior with collapsed children

Author: michael-hawker

Microsoft.Toolkit.Uwp.UI.Controls.Primitives/WrapPanel/WrapPanel.cs

@@ -166,6 +166,13 @@ protected override Size ArrangeOverride(Size finalSize)
                     foreach (var rect in row.ChildrenRects)
                     {
                         var child = Children[childIndex++];
+                        while (child.Visibility == Visibility.Collapsed)
+                        {
+                            // Collapsed children are not added into the rows,
+                            // we skip them.
+                            child = Children[childIndex++];
+                        }
+
                         var arrangeRect = new UvRect
                         {
                             Position = rect.Position,
@@ -202,12 +209,12 @@ private Size UpdateRows(Size availableSize)
             var finalMeasure = new UvMeasure(Orientation, width: 0.0, height: 0.0);
             void Arrange(UIElement child, bool isLast = false)
             {
-                var desiredMeasure = new UvMeasure(Orientation, child.DesiredSize);
-                if (desiredMeasure.U == 0)
+                if (child.Visibility == Visibility.Collapsed)
                 {
                     return; // if an item is collapsed, avoid adding the spacing
                 }
 
+                var desiredMeasure = new UvMeasure(Orientation, child.DesiredSize);
                 if ((desiredMeasure.U + position.U + paddingEnd.U) > parentMeasure.U)
                 {
                     // next row!