结构调整，便于后续扩展

AIStudio.Wpf.BaseDiagram/Converters/RulerUnitConverter.cs

@@ -0,0 +1,36 @@
+using AIStudio.Wpf.BaseDiagram.Controls;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Data;
+using Util.DiagramDesigner;
+
+namespace AIStudio.Wpf.BaseDiagram.Converters
+{
+    public class RulerUnitConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
+        {
+            if (value is PageUnit pageunit)
+            {
+                if (pageunit > PageUnit.km)
+                {
+                    return Unit.Inch;
+                }
+                else
+                {
+                    return Unit.Cm;
+                }
+            }
+
+            return value;
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}