feat: Enable Rules from 1826 to 1829

.editorconfig

@@ -145,6 +145,14 @@ dotnet_diagnostic.CA1820.severity = warning
 dotnet_diagnostic.CA1821.severity = warning
 # CA1825: Avoid zero-length array allocations
 dotnet_diagnostic.CA1825.severity = warning
+# CA1826: Use property instead of Linq Enumerable method
+dotnet_diagnostic.CA1826.severity = suggestion
+# CA1827: Do not use Count/LongCount when Any can be used
+dotnet_diagnostic.CA1827.severity = warning
+# CA1828: Do not use CountAsync/LongCountAsync when AnyAsync can be used
+dotnet_diagnostic.CA1828.severity = warning
+# CA1829: Use Length/Count property instead of Enumerable.Count method
+dotnet_diagnostic.CA1829.severity = warning
 #CA1847: Use string.Contains(char) instead of string.Contains(string) with single characters
 dotnet_diagnostic.CA1847.severity = warning
 

src/Avalonia.Controls/Selection/SelectionNodeBase.cs

@@ -290,12 +290,12 @@ namespace Avalonia.Controls.Selection
             // so bail.
             //
             // See unit test Handles_Selection_Made_In_CollectionChanged for more details.
-            if (ItemsView is object &&
+            if (ItemsView is not null &&
                 RangesEnabled &&
                 Ranges.Count > 0 &&
                 e.Action == NotifyCollectionChangedAction.Add)
             {
-                var lastIndex = Ranges.Last().End;
+                var lastIndex = Ranges[Ranges.Count - 1].End;
 
                 if (e.NewStartingIndex <= lastIndex)
                 {