c# - 使用 foreach 循环和 XmlNodeList C# 将新节点附加到节点列表

Question

目前我正在处理的是 XML 类型:XML FILE

引用 XML 文件，我想检查一个节点，如果找不到该节点，我必须将该节点附加到文件中。我尝试了以下代码:

 private void button12_Click(object sender, EventArgs e)
    {
     //   XmlNodeList func_name_value = doc.GetElementsByTagName("FUNCTION-NAME-VALUE");
        XmlNodeList list_def_ref = doc.GetElementsByTagName("DEFINITION-REF");
        foreach (XmlNode nodeDef in list_def_ref)
        {
            if (nodeDef.InnerText == "/AUTOSAR/Com/ComConfig/ComSignal")
                {
                    if (nodeDef.ParentNode.HasChildNodes)
                    {
                        XmlNodeList list = nodeDef.ParentNode.ChildNodes;
                        foreach (XmlNode node in list)
                        {
                            if (node.Name == "PARAMETER-VALUES")
                            {
                                XmlNodeList param_list = node.ChildNodes;
                                foreach (XmlNode paramNode in param_list)
                                {
                                    if (paramNode.Name == "FUNCTION-NAME-VALUE")
                                    {
                                        XmlNodeList func_child_list = paramNode.ChildNodes;
                                        foreach (XmlNode funChild in func_child_list)
                                        {
                                            if (funChild.Name == "DEFINITION-REF")
                                            {
                                                string tout = "/AUTOSAR/Com/ComConfig/ComSignal/ComTimeoutNotification";
                                                string comnotify = "/AUTOSAR/Com/ComConfig/ComSignal/ComNotification";
                                                string invalid = "/AUTOSAR/Com/ComConfig/ComSignal/ComInvalidNotification";
                                                if (funChild.InnerText != tout)
                                                {
                                                    if (funChild.InnerText != comnotify)
                                                    {
                                                        //ADD ComInvalidNotification tags
                                                        XmlNode newNode = doc.CreateElement("FUNCTION-NAME-VALUE");
                                                        paramNode.AppendChild(newNode);
                                                        XmlNode defRefNode = doc.CreateElement("DEFINITION-REF");
                                                        XmlAttribute attr = doc.CreateAttribute("DEST");
                                                        attr.Value = "FUNCTION-NAME-DEF";
                                                        defRefNode.Attributes.SetNamedItem(attr);
                                                        newNode.AppendChild(defRefNode);
                                                        XmlNode val = doc.CreateElement("VALUE");
                                                        val.InnerText = "ComInvalidNotification";//ComInvalidNotification + shortName ;
                                                        newNode.AppendChild(val);
                                                    }
                                                    else
                                                    {
                                                        //ADD ComNotification tags
                                                        XmlNode newNode = doc.CreateElement("FUNCTION-NAME-VALUE");
                                                        paramNode.AppendChild(newNode);
                                                        XmlNode defRefNode = doc.CreateElement("DEFINITION-REF");
                                                        XmlAttribute attr = doc.CreateAttribute("DEST");
                                                        attr.Value = "FUNCTION-NAME-DEF";
                                                        defRefNode.Attributes.SetNamedItem(attr);
                                                        newNode.AppendChild(defRefNode);
                                                        XmlNode val = doc.CreateElement("VALUE");
                                                        val.InnerText = "ComNotification Node";//ComNotification + shortName;
                                                        newNode.AppendChild(val);
                                                    }
                                                }
                                                else
                                                {
                                                    //ADD ComTimeOutNotification tags
                                                    XmlNode newNode = doc.CreateElement("FUNCTION-NAME-VALUE");
                                                    paramNode.AppendChild(newNode);
                                                    XmlNode defRefNode = doc.CreateElement("DEFINITION-REF");
                                                    XmlAttribute attr = doc.CreateAttribute("DEST");
                                                    attr.Value = "FUNCTION-NAME-DEF";
                                                    defRefNode.Attributes.SetNamedItem(attr);
                                                    newNode.AppendChild(defRefNode);
                                                    XmlNode val = doc.CreateElement("VALUE");
                                                    val.InnerText = "ComTimeoutNotification node";//ComInvalidNotification + shortName;
                                                    newNode.AppendChild(val);
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }

        doc.Save(openFileDialog1.FileName);

我收到的错误是:元素列表已更改。枚举操作未能继续。

第一次执行 foreach 循环后，出现此错误，我该如何解决此错误？

Answer 1

这里有两个问题:

1. 您正在修改您的 XmlNodeList集合，同时遍历它们。 Microsoft 的标准做法是在迭代期间修改集合时抛出异常，例如参见 IEnumerator.MoveNext 的文档:

   Exceptions

   InvalidOperationException: The collection was modified after the enumerator was created.

   要避免此异常，您可以使用 for通过 XmlNodeList 循环和索引手动，或 snapshot to a static List<T> and iterate through that .

2. 您正在搜索名为 <DEFINITION-REF> 的 XML 节点和 <FUNCTION-NAME-VALUE> ，但您还创建具有此名称的节点。这意味着您在迭代早期创建的节点可能会在迭代后期找到，从而导致递归创建更多节点。我想你不想要这个。如果我的估计是正确的，您应该对所有符合搜索条件的节点进行快照，然后遍历快照，如下所示:

   private static void AddMissingNodes(XmlDocument doc)
   {
       var query = from nodeDef in doc.GetElementsByTagName("DEFINITION-REF").Cast<XmlNode>()
                   where nodeDef.InnerText == "/AUTOSAR/Com/ComConfig/ComSignal"
                   from nodeDefSibling in nodeDef.ParentNode.ChildNodes.Cast<XmlNode>()
                   where nodeDefSibling.Name == "PARAMETER-VALUES"
                   from paramNode in nodeDefSibling.ChildNodes.Cast<XmlNode>()
                   where paramNode.Name == "FUNCTION-NAME-VALUE"
                   select new
                   {
                       paramNode = paramNode,
                       func_child_list = (from funChild in paramNode.ChildNodes.Cast<XmlNode>()
                                         where funChild.Name == "DEFINITION-REF"
                                          select funChild).ToList() // Snapshot func_child_list by calling ToList()
                   };
   
       foreach (var paramNodeAndFuncChildren in query.ToList()) // Snapshot everything by calling ToList()
           foreach (var funChild in paramNodeAndFuncChildren.func_child_list)
               AddMissingNodes(doc, paramNodeAndFuncChildren.paramNode, funChild);
   
   }
   
   private static void AddMissingNodes(XmlDocument doc, XmlNode paramNode, XmlNode funChild)
   {
       string tout = "/AUTOSAR/Com/ComConfig/ComSignal/ComTimeoutNotification";
       string comnotify = "/AUTOSAR/Com/ComConfig/ComSignal/ComNotification";
       string invalid = "/AUTOSAR/Com/ComConfig/ComSignal/ComInvalidNotification";
       if (funChild.InnerText != tout)
       {
           if (funChild.InnerText != comnotify)
           {
               //ADD ComInvalidNotification tags
               XmlNode newNode = doc.CreateElement("FUNCTION-NAME-VALUE");
               paramNode.AppendChild(newNode);
               XmlNode defRefNode = doc.CreateElement("DEFINITION-REF");
               XmlAttribute attr = doc.CreateAttribute("DEST");
               attr.Value = "FUNCTION-NAME-DEF";
               defRefNode.Attributes.SetNamedItem(attr);
               newNode.AppendChild(defRefNode);
               XmlNode val = doc.CreateElement("VALUE");
               val.InnerText = "ComInvalidNotification";//ComInvalidNotification + shortName ;
               newNode.AppendChild(val);
           }
           else
           {
               //ADD ComNotification tags
               XmlNode newNode = doc.CreateElement("FUNCTION-NAME-VALUE");
               paramNode.AppendChild(newNode);
               XmlNode defRefNode = doc.CreateElement("DEFINITION-REF");
               XmlAttribute attr = doc.CreateAttribute("DEST");
               attr.Value = "FUNCTION-NAME-DEF";
               defRefNode.Attributes.SetNamedItem(attr);
               newNode.AppendChild(defRefNode);
               XmlNode val = doc.CreateElement("VALUE");
               val.InnerText = "ComNotification Node";//ComNotification + shortName;
               newNode.AppendChild(val);
           }
       }
       else
       {
           //ADD ComTimeOutNotification tags
           XmlNode newNode = doc.CreateElement("FUNCTION-NAME-VALUE");
           paramNode.AppendChild(newNode);
           XmlNode defRefNode = doc.CreateElement("DEFINITION-REF");
           XmlAttribute attr = doc.CreateAttribute("DEST");
           attr.Value = "FUNCTION-NAME-DEF";
           defRefNode.Attributes.SetNamedItem(attr);
           newNode.AppendChild(defRefNode);
           XmlNode val = doc.CreateElement("VALUE");
           val.InnerText = "ComTimeoutNotification node";//ComInvalidNotification + shortName;
           newNode.AppendChild(val);
       }
   }
   

   然后，如果我count the number of XML nodes之前和之后:

       var fileName = @"D:\Temp\Question36740480\autosar_ecucvalues_Fx4_L.xml";
       var newFileName = @"D:\Temp\Question36740480\autosar_ecucvalues_Fx4_L_NEW.xml";
   
       var doc = new XmlDocument();
       doc.Load(fileName);
   
       int countBefore = doc.SelectNodes("descendant::*").Count;
   
       AddMissingNodes(doc);
   
       int countAfter = doc.SelectNodes("descendant::*").Count;
   
       Debug.WriteLine(string.Format("Added {0} nodes", countAfter - countBefore));
   
       doc.Save(newFileName);
   
       Debug.WriteLine("Wrote: " + newFileName);
   

   我看到 XmlDocument 添加了 342 个节点.