加上缩进，输出xml字符串，代码：
using System.Xml;
using System.Text;
/// <summary>
/// Format xml string without indent
/// to xml string with indent
/// </summary>
/// <param name="source">xml string without indent </param>
/// <returns>xml string with indent </returns>
private string FormatXml(string source)
{
StringBuilder sb = new StringBuilder();
XmlTextWriter writer = null;
try
{
XmlDocument doc = new XmlDocument();
doc.LoadXml(source);
writer = new XmlTextWriter(new StringWriter(sb));
writer.Formatting = Formatting.Indented;
doc.WriteTo(writer);
}
finally
{
if (writer != null) writer.Close();
}
return sb.ToString();
}