Code refactoring, avoid exceptions for invalid offsets

Author: Sergio0694

Microsoft.Toolkit.Uwp.UI.Controls/UniformGrid/TakenSpotsReferenceHolder.cs

@@ -3,6 +3,8 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Collections;
+using System.Drawing;
+using System.Runtime.CompilerServices;
 using Microsoft.Toolkit.Diagnostics;
 
 namespace Microsoft.Toolkit.Uwp.UI.Controls
@@ -57,6 +59,31 @@ public TakenSpotsReferenceHolder(int rows, int columns)
             set => this.spotsTaken[(i * Width) + j] = value;
         }
 
+        /// <summary>
+        /// Fills the specified area in the current grid with a given value.
+        /// If invalid coordinates are given, they will simply be ignored and no exception will be thrown.
+        /// </summary>
+        /// <param name="value">The value to fill the target area with.</param>
+        /// <param name="row">The row to start on (inclusive, 0-based index).</param>
+        /// <param name="column">The column to start on (inclusive, 0-based index).</param>
+        /// <param name="width">The positive width of area to fill.</param>
+        /// <param name="height">The positive height of area to fill.</param>
+        public void Fill(bool value, int row, int column, int width, int height)
+        {
+            Rectangle bounds = new Rectangle(0, 0, Width, Height);
+
+            // Precompute bounds to skip branching in main loop
+            bounds.Intersect(new Rectangle(column, row, width, height));
+
+            for (int i = bounds.Top; i < bounds.Bottom; i++)
+            {
+                for (int j = 0; j < bounds.Width; j++)
+                {
+                    this[i, j] = value;
+                }
+            }
+        }
+
         /// <summary>
         /// Resets the current reference holder.
         /// </summary>

Microsoft.Toolkit.Uwp.UI.Controls/UniformGrid/UniformGrid.cs

@@ -18,7 +18,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     public partial class UniformGrid : Grid
     {
         // Guard for 15063 as Grid Spacing only works on 16299+.
-        private static bool _hasGridSpacing = ApiInformation.IsPropertyPresent("Windows.UI.Xaml.Controls.Grid", "ColumnSpacing");
+        private static readonly bool _hasGridSpacing = ApiInformation.IsPropertyPresent("Windows.UI.Xaml.Controls.Grid", "ColumnSpacing");
 
         // Internal list we use to keep track of items that we don't have space to layout.
         private List<UIElement> _overflow = new List<UIElement>();
@@ -78,14 +78,7 @@ protected override Size MeasureOverride(Size availableSize)
                 {
                     SetAutoLayout(child, false);
 
-                    // Fill the area covered by the current element
-                    for (int i = 0; i < rowspan; i++)
-                    {
-                        for (int j = 0; j < colspan; j++)
-                        {
-                            spotref[row + i, col + j] = true;
-                        }
-                    }
+                    spotref.Fill(true, row, col, colspan, rowspan);
                 }
             }
 
@@ -133,15 +126,7 @@ protected override Size MeasureOverride(Size availableSize)
                         if (rowspan > 1 || colspan > 1)
                         {
                             // TODO: Need to tie this into iterator
-
-                            // Fill the covered area as above
-                            for (int i = 0; i < rowspan; i++)
-                            {
-                                for (int j = 0; j < colspan; j++)
-                                {
-                                    spotref[row + i, column + j] = true;
-                                }
-                            }
+                            spotref.Fill(true, row, column, colspan, rowspan);
                         }
                     }
                     else