支持多个node保存到工具栏，显示还有点问题。

AIStudio.Wpf.DiagramDesigner/ViewModels/BaseViewModel/DiagramViewModelHelper.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace AIStudio.Wpf.DiagramDesigner
+{
+    public class DiagramViewModelHelper
+    {
+        public static DesignerItemViewModelBase GetConnectorDataItem(IEnumerable<SelectableDesignerItemViewModelBase> items, Guid conectorDataItemId, Type connectorDataItemType)
+        {
+            DesignerItemViewModelBase dataItem = items.OfType<DesignerItemViewModelBase>().Single(x => x.Id == conectorDataItemId);
+            return dataItem;
+        }
+    }
+}