添加了变量表的停用和启用功能，并优化了添加变量表和添加设备的逻辑

ViewModels/ViewModelBase.cs

@@ -4,6 +4,16 @@ namespace PMSWPF.ViewModels;
 
 public abstract class ViewModelBase : ObservableObject
 {
-    public Object NavgateParameters { get; set; }
-    public abstract void OnLoaded();
+    public virtual void OnLoaded()
+    {
+        
+    }
+
+    public virtual void OnLoading()
+    {
+        
+    }
+
+
+
 }