XDocument xdoc = XDocument.Load("data.xml");
var lv1s = xdoc.Root.Descendants("level1"); 
var lvs = lv1s.SelectMany(l=>
     new string[]{ l.Attribute("name").Value }
     .Union(
         l.Descendants("level2")
         .Select(l2=>"   " + l2.Attribute("name").Value)
      )
    );
foreach (var lv in lvs)
{
   result.AppendLine(lv);
}

Ps.你必须在这些版本中使用. root。

XML文件的异步加载可以提高性能，特别是在文件很大或加载时间较长的情况下。在本例中，我们使用XDocument。LoadAsync方法来异步加载和解析XML文件，这有助于防止在加载文件时应用程序失去响应。

演示:https://dotnetfiddle.net/PGFE7c(使用XML字符串解析)

实现:

XDocument doc;

// Open the XML file using File.OpenRead and pass the stream to 
// XDocument.LoadAsync to load and parse the XML asynchronously
using (var stream = File.OpenRead("data.xml"))
{
    doc = await XDocument.LoadAsync(stream, LoadOptions.None, CancellationToken.None);
}

// Select the level1 elements from the document and create an anonymous object for each element
// with a Name property containing the value of the "name" attribute and a Children property
// containing a collection of the names of the level2 elements
var results = doc.Descendants("level1")
                .Select(level1 => new
                {
                    Name = level1.Attribute("name").Value,
                    Children = level1.Descendants("level2")
                                     .Select(level2 => level2.Attribute("name").Value)
                });

foreach (var result in results)
{
    Console.WriteLine(result.Name);
    foreach (var child in result.Children)
        Console.WriteLine("  " + child);
}

结果:

A
  A1
  A2
B
  B1
  B2
C

或者，如果你想要一个更通用的方法-即嵌套到“levelN”:

void Main()
{
    XElement rootElement = XElement.Load(@"c:\events\test.xml");

    Console.WriteLine(GetOutline(0, rootElement));  
}

private string GetOutline(int indentLevel, XElement element)
{
    StringBuilder result = new StringBuilder();

    if (element.Attribute("name") != null)
    {
        result = result.AppendLine(new string(' ', indentLevel * 2) + element.Attribute("name").Value);
    }

    foreach (XElement childElement in element.Elements())
    {
        result.Append(GetOutline(indentLevel + 1, childElement));
    }

    return result.ToString();
}

几个简单的foreach循环提供了一个干净的解决方案:

foreach (XElement level1Element in XElement.Load("data.xml").Elements("level1"))
{
    result.AppendLine(level1Element.Attribute("name").Value);

    foreach (XElement level2Element in level1Element.Elements("level2"))
    {
        result.AppendLine("  " + level2Element.Attribute("name").Value);
    }
}

XDocument xdoc = XDocument.Load("data.xml");
var lv1s = xdoc.Root.Descendants("level1"); 
var lvs = lv1s.SelectMany(l=>
     new string[]{ l.Attribute("name").Value }
     .Union(
         l.Descendants("level2")
         .Select(l2=>"   " + l2.Attribute("name").Value)
      )
    );
foreach (var lv in lvs)
{
   result.AppendLine(lv);
}

Ps.你必须在这些版本中使用. root。

试试这个。

using System.Xml.Linq;

void Main()
{
    StringBuilder result = new StringBuilder();

    //Load xml
    XDocument xdoc = XDocument.Load("data.xml");

    //Run query
    var lv1s = from lv1 in xdoc.Descendants("level1")
               select new { 
                   Header = lv1.Attribute("name").Value,
                   Children = lv1.Descendants("level2")
               };

    //Loop through results
    foreach (var lv1 in lv1s){
            result.AppendLine(lv1.Header);
            foreach(var lv2 in lv1.Children)
                 result.AppendLine("     " + lv2.Attribute("name").Value);
    }

    Console.WriteLine(result);
}