Fix bug with UniformGridLayout MaximumRowsOrColumns and requested size (#1802)

* Add test for UniformGridLayout measure bug

* Update test so it actually tests #1549

* Fix bug with stretching of UniformGridLayout when it should not

* Fix indentation

Author: marcelwgn

dev/Repeater/APITests/FlowLayoutTests.cs

@@ -580,6 +580,64 @@ public void ValidateGridLayoutMaximumRowsOrColumns()
             });
         }
 
+        [TestMethod]
+        public void ValidateGridLayoutDesiredSizingWithMaxRowsOrColumnsSet()
+        {
+            RunOnUIThread.Execute(() =>
+            {
+                foreach (ScrollOrientation scrollOrientation in Enum.GetValues(typeof(ScrollOrientation)))
+                {
+                    Log.Comment(string.Format("ScrollOrientation: {0}", scrollOrientation));
+                    var om = new OrientationBasedMeasures(scrollOrientation, useLayoutRounding: true);
+                    const int numItems = 4;
+
+                    int itemSize = 100;
+
+                    LayoutPanel panel = new LayoutPanel();
+                    var layout = new UniformGridLayout() {
+                        Orientation = scrollOrientation.ToOrthogonalLayoutOrientation(),
+                        ItemsJustification = UniformGridLayoutItemsJustification.Start,
+                        MinItemWidth = itemSize,
+                        MinItemHeight = itemSize,
+                        MinRowSpacing = 0,
+                        MinColumnSpacing = 0
+                    };
+                    
+                    for (int i = 0; i < numItems; i++)
+                    {
+                        panel.Children.Add(new Button() { Content = i,Width = itemSize,Height = itemSize });
+                    }
+                    
+                    panel.Layout = layout;
+                    Content = panel;
+
+                    // Place in top left corner to prevent stretch of panel
+                    panel.VerticalAlignment = VerticalAlignment.Top;
+                    panel.HorizontalAlignment = HorizontalAlignment.Left;
+                    layout.ItemsJustification = UniformGridLayoutItemsJustification.Start;
+
+                    for(int i = 1; i < numItems; i++)
+                    {
+                        layout.MaximumRowsOrColumns = i;
+                        panel.UpdateLayout();
+
+                        if (om.IsVerical)
+                        {
+                            // Vertical so fill columns first
+                            Verify.AreEqual(itemSize * i, panel.DesiredSize.Width);
+                            Verify.AreEqual(Math.Ceiling((double)numItems / (double)i) * itemSize, panel.DesiredSize.Height);
+                        }
+                        else
+                        {
+                            // Horizontal, fill rows first
+                            Verify.AreEqual(itemSize * i, panel.DesiredSize.Height);
+                            Verify.AreEqual(Math.Ceiling((double)numItems / (double)i) * itemSize, panel.DesiredSize.Width);
+                        }
+                    }
+
+                }
+            });
+        }
 
         [TestMethod]
         public void ValidateFlowLayout()

dev/Repeater/UniformGridLayout.cpp

@@ -213,10 +213,11 @@ winrt::Rect UniformGridLayout::Algorithm_GetExtent(
 
     if (itemsCount > 0)
     {
+        // Only use all of the space if item stretch is fill, otherwise size layout according to items placed
         extent.*MinorSize() =
-            std::isfinite(availableSizeMinor) ?
+            std::isfinite(availableSizeMinor) && m_itemsStretch == winrt::UniformGridLayoutItemsStretch::Fill ?
             availableSizeMinor :
-            std::max(0.0f, itemsCount * GetMinorSizeWithSpacing(context) - static_cast<float>(MinItemSpacing()));
+            std::max(0.0f, itemsPerLine * GetMinorSizeWithSpacing(context) - static_cast<float>(MinItemSpacing()));
         extent.*MajorSize() = std::max(0.0f, (itemsCount / itemsPerLine) * lineSize - static_cast<float>(LineSpacing()));
 
         if (firstRealized)