重写了节点的view、viewmodel关系，实现了对画布元素的选取功能，重构了底层依赖，添加了对net .Framework4.6.1以上的Framework类库支持

Library.Core/Flow/NodeModel/SingleExpOpNode.cs

@@ -0,0 +1,35 @@
+using Serein.Flow.SerinExpression;
+
+namespace Serein.Flow.NodeModel
+{
+    /// <summary>
+    /// Expression Operation - 表达式操作
+    /// </summary>
+    public class SingleExpOpNode : NodeBase
+    {
+        /// <summary>
+        /// 表达式
+        /// </summary>
+        public string Expression { get; set; }
+
+
+        public override object? Execute(DynamicContext context)
+        {
+            var data = PreviousNode?.FlowData;
+
+            var newData = SerinExpressionEvaluator.Evaluate(Expression, data, out bool isChange);
+
+            FlowState = true;
+            Console.WriteLine(newData);
+            if (isChange)
+            {
+                return newData;
+            }
+            else
+            {
+                return PreviousNode?.FlowData;
+            }
+
+        }
+    }
+}