C# 从 xml 属性中获取值

Question

How to get attribute "action" and "filename" values in a right way using C#?

XML:

<?xml version="1.0" encoding="utf-8" ?>
 <Config version="1.0.1.1" >
   <Items>
    <Item action="Create" filename="newtest.xml"/>
    <Item action="Update" filename="oldtest.xml"/>   
  </Items>
 </Config>

C#: i cannot get attribute values as well as how to get values in foreach loops? How to solve this?

        var doc = new XmlDocument();
        doc.Load(@newFile);
        var element = ((XmlElement)doc.GetElementsByTagName("Config/Items/Item")[0]); //null
        var xmlActions = element.GetAttribute("action"); //cannot get values
        var xmlFileNames= element.GetAttribute("filename"); //cannot get values

         foreach (var action in xmlActions)
         {
           //not working
         }

         foreach (var file in xmlFileNames)
         {
           //not working
         }

Your code example means alot to me. Thanks!

Answer 1

You can use LINQ to XML . Following query returns strongly typed collection of items with Action and FileName properties:

var xdoc = XDocument.Load(@newFile);

var items = from i in xdoc.Descendants("Item")
            select new {
               Action = (string)i.Attribute("action"),
               FileName = (string)i.Attribute("fileName")
            };

foreach (var item in items)
{
   // use item.Action or item.FileName
}

Answer 2

GetElementsByTagName will find you only direct descendants. The argument is supposed to be just a tag name , not a whole path of elements.

If you want to search across the document while supplying an XPath expression, use SelectNodes instead.

For your document, it should look like this:

var element = (XmlElement)doc.SelectNodes("/Config/Items/Item")[0];

Answer 3

You can achieve what you're asking with LINQ to XML :

// For each element that is a child of your Items element that is named Item
foreach (var item in XElement.Load("file.xml").Descendants("Items").Elements("Item"))
{
    // If the element does not have any attributes
    if (!item.Attributes().Any())
    {
        // Lets skip it
        continue;
    }

    // Obtain the value of your action attribute - Possible null reference exception here that should be handled
    var action = item.Attribute("action").Value;
    // Obtain the value of your filename attribute - Possible null reference exception here that should be handled
    var filename = item.Attribute("filename").Value;

    // Do something with your data
    Console.WriteLine("action: {0}, filename {1}", action, filename);
}

Answer 4

There are a bunch of problems with the code in the question:
1. You are using an XPath in the GetElementsByTagName, just use the tag
2. You are only getting the first XmlNode in the XmlNodeCollection by using [0]
3. Since you only have one XmlNode, you are only getting a string result for getting the attribute, not a collection of strings, which you are then trying to enumerate through
4. Your foreach is broken, there is no type for the resulting object

Here is a snippet that would work:

var doc = new XmlDocument();
doc.Load("test.xml");
var items = doc.GetElementsByTagName("Item");

var xmlActions = new string[items.Count];
var xmlFileNames = new string[items.Count];
for (int i = 0; i < items.Count; i++) {
    var xmlAttributeCollection = items[i].Attributes;
    if (xmlAttributeCollection != null) {
        var action = xmlAttributeCollection["action"];
        xmlActions[i] = action.Value;

        var fileName = xmlAttributeCollection["filename"];
        xmlFileNames[i] = fileName.Value;
    }
}

foreach (var action in xmlActions) {
    //working
}

foreach (var file in xmlFileNames) {
    //working
}

Or, if you don't need all of the actions and filenames in a collection before you act on them, you could just act on each action/filename in the for loop.