mind多个根节点的时候，切换模式的修复

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

@@ -1050,10 +1050,12 @@ namespace AIStudio.Wpf.DiagramDesigner
         {
             Mediator.Instance.Register(this);
             Items.CollectionChanged += Items_CollectionChanged;
+            
             var zoomValueChangedSubscription = WhenPropertyChanged.Where(o => o.ToString() == nameof(ZoomValue)).Throttle(TimeSpan.FromMilliseconds(100)).Subscribe(OnZoomValueChanged);//Sample
-           
+            this.PropertyChanged += DiagramViewModel_PropertyChanged;
             BuildMenuOptions();
         }
+
         public DiagramViewModel(DiagramItem diagramItem) : this()
         {
             DiagramType = diagramItem.DiagramType;
@@ -1161,6 +1163,11 @@ namespace AIStudio.Wpf.DiagramDesigner
         #endregion
 
         #region 属性改变
+        protected virtual void DiagramViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
+        {
+            
+        }
+
         private void Items_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
         {
             if (e.OldItems != null)