chore: add avalonia Expander demo.

src/Shared/HandyControl_Shared/Tools/Converter/CornerRadiusSplitConverter.cs

@@ -9,21 +9,24 @@ public class CornerRadiusSplitConverter : IValueConverter
 {
     public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
     {
-        if (value is CornerRadius cornerRadius)
+        if (value is not CornerRadius cornerRadius)
         {
-            if (parameter is string str)
-            {
-                var arr = str.Split(',');
-                if (arr.Length != 4) return cornerRadius;
-
-                return new CornerRadius(
-                    arr[0].Equals("1") ? cornerRadius.TopLeft : 0,
-                    arr[1].Equals("1") ? cornerRadius.TopRight : 0,
-                    arr[2].Equals("1") ? cornerRadius.BottomRight : 0,
-                    arr[3].Equals("1") ? cornerRadius.BottomLeft : 0);
-            }
+            return value;
         }
-        return value;
+
+        if (parameter is not string str)
+        {
+            return value;
+        }
+
+        var arr = str.Split(',');
+        if (arr.Length != 4) return cornerRadius;
+
+        return new CornerRadius(
+            arr[0].Trim().Equals("1") ? cornerRadius.TopLeft : 0,
+            arr[1].Trim().Equals("1") ? cornerRadius.TopRight : 0,
+            arr[2].Trim().Equals("1") ? cornerRadius.BottomRight : 0,
+            arr[3].Trim().Equals("1") ? cornerRadius.BottomLeft : 0);
     }
 
     public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)