Question

XmlTextReader to read Attributes from xml string - C#

Asked by: NewMom2Brandon

Simple Question, but need it quickly.  My server application receives an xml string which I am trying
to read using XmlTextReader.  I am having a problem getting it to recognize an attribute and retrieving the data.
This is the latest I have tried:
It seems when I step through the debugger, it does not seem to recognize that it even has an attribute associated with
an element.   What do I need to do?    



XML String:
<?xml version="1.0" encoding= "utf-8" ?>
<Message>
<Name>Name</Name>
<DateTime>1/24/2005 :00:23PM</DateTime>
<Machine>MachineName</Machine>
<MessageNumber>999</MessageNumber>
<Detail Type = "Detail1">Text1</Detail>
<Detail Type = "Detail2">Text2</Detail>
</Message>

To Read The Data:

XmlTextReader reader = new XmlTextReader(sXmlString);

while (reader.Read())
{
   if (reader.NodeType.Equals(XmlNodeType.Element))
  {
     sNode = reader.Name;
     sValue = reader.Value;

     switch (sNode)
{
      case "Name":
     case "DateTime":
     case "MachineName" :
    case "MessageNumber" :
  //do stuff
   break;
    case "Detail":
                                                 
   if (reader.HasAttributes)    // This fails every time
      sattribute = reader.GetAttribute("Type");

//I've also tried this
   while (reader.MoveToNextAttribute())  // This also failed
  {
     if (reader.Name.Equals("Type"))
         m_DetailList.Add(reader.Value);
  }
   reader.MoveToElement();
      
//And Tried This
  else if (reader.NodeType.Equals(XmlNodeType.Attribute)) //failed
  {
  string svalue;
  string snode;

 svalue = reader.Value;
 snode = reader.Name;
System.Diagnostics.EventLog.WriteEntry(this.ToString(),
"DetailAttrName: " + reader.Name);

System.Diagnostics.EventLog.WriteEntry(this.ToString(),
"DetailText: " + reader.Value);
   }
}

 







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Asked On
2005-01-25 at 08:54:35ID21287911
Tags

element

,

xml

,

xmltextreader

,

attribute

,

string

Topics

Extensible Markup Language (XML)

,

Extensible HTML (XHTML)

Participating Experts
1
Points
500
Comments
7

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Answers

 

by: dualsoulPosted on 2005-01-25 at 10:19:39ID: 13134804

hm...not sure what doesn't work with your code.

It seems absolutely allright :)

here the my test class, check it yourself:
using System;
using System.Xml;
using System.IO;
namespace ConsoleApplication1 {
    /// <summary>
    /// Summary description for Class1.
    /// </summary>
    class Class1 {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main(string[] args) {
            XmlTextReader reader = new XmlTextReader(new FileStream("test.xml",FileMode.OpenOrCreate));

            while (reader.Read()) {                
                if (reader.NodeType.Equals(XmlNodeType.Element)) {
                   
                    switch (reader.Name) {
                        case "Name": Console.WriteLine("Name");
                                     break;
                        case "DateTime":Console.WriteLine("DateTie");
                                     break;
                        case "MachineName" :Console.WriteLine("MachineName");
                            break;
                        case "MessageNumber" :Console.WriteLine("MessageNumber");                                
                            break;
                        case "Detail": Console.WriteLine("Details");
                            if (reader.HasAttributes)    // This fails every time
                                Console.WriteLine("Attribute @type: "+reader.GetAttribute("Type"));
                            break;
                    }          
                }
            }
        }
    }
}

 

by: NewMom2BrandonPosted on 2005-01-25 at 12:31:48ID: 13136126


Now I'm even more confused.
I tried the TestApp and it worked fine.

Again I doublechecked my app - I still get null returned for reader.GetAttribute("Type")
and a false for reader.HasAttributes.

The only thing that's different is that I'm not creating the XmlTextReader from
a file. But that shouldn't make a difference, should it?
I'm at a loss.

Is there another way that I can get this data, perhaps not using XmlTextReader?



 

by: dualsoulPosted on 2005-01-25 at 23:43:17ID: 13139657

hm...here is the version that reads xml from string:

using System;
using System.Xml;
using System.IO;
namespace ConsoleApplication1 {
      /// <summary>
      /// Summary description for Class1.
      /// </summary>
      class Class1 {
            /// <summary>
            /// The main entry point for the application.
            /// </summary>
            [STAThread]
            static void Main(string[] args) {
                  string xml=
                        "<?xml version=\"1.0\" encoding= \"utf-8\" ?>"+
                        "<Message>"+                        
                        "<Name>Name</Name>"+
                        "<DateTime>1/24/2005 :00:23PM</DateTime>"+
                        "<Machine>MachineName</Machine>"+
                        "<MessageNumber>999</MessageNumber>"+
                        "<Detail Type = \"Detail1\">Text1</Detail>"+
                        "<Detail Type = \"Detail2\">Text2</Detail>"+
                        "</Message>";

                  XmlTextReader reader = new XmlTextReader(new StringReader(xml));
                  
                  
                  
                        while (reader.Read()) {                
                              if (reader.NodeType.Equals(XmlNodeType.Element)) {
                   
                                    switch (reader.Name) {
                                          case "Name": Console.WriteLine("Name");
                                                break;
                                          case "DateTime":Console.WriteLine("DateTie");
                                                break;
                                          case "MachineName" :Console.WriteLine("MachineName");
                                                break;
                                          case "MessageNumber" :Console.WriteLine("MessageNumber");                                
                                                break;
                                          case "Detail": Console.WriteLine("Details");
                                                if (reader.HasAttributes)    // This fails every time
                                                      Console.WriteLine("Attribute @type: "+reader.GetAttribute("Type"));
                                                break;
                                    }          
                              }
                        }
                  }
            }
      }


, now it's nearly the yours original. Try.

 

by: NewMom2BrandonPosted on 2005-01-26 at 08:09:27ID: 13143368


Ok, I got that to work somehow. In the case statements, I use a
In the case statements of Name, DateTime, MachineName, MessageNumber, I use

reader.ReadElementString();

I now notice that this moves the node and I was pointing at an end element.
So it didn't see the attribute.
I have the issue now where it moves forward everytime it reads and when the
reader.Read() gets hit, it at times lands on a text node, skips the parsing (since its not an element), and
moves reads to the next node. In my example it ends up skipping a couple nodes. Which doesn't make much sense
to me, since they all have end elements.
Is there a way to read the text node without moving the reader forward?  Or maybe theres a reason why it skips
some and not others. Any suggestions would be great :)

while (reader.Read())
{  
    string sValue;

    if (reader.NodeType.Equals(XmlNodeType.Element))
    {
       switch (reader.Name)
       {
            case "Name":
                  sValue = reader.ReadElementString(); //forwards the reader
                  m_sName = sValue;
                  break;
            case "DateTime":
                  sValue = reader.ReadElementString();
                  m_ReceivedTime = DateTime.Parse(sValue);
                  break;
            case "Machine":
                  sValue = reader.ReadElementString();
                  m_sMachineName = sValue;
                  break;
            case "MessageNumber":
                  sValue = reader.ReadElementString();
                  m_iMessageNum = Convert.ToInt32(sValue);
                  break;
            case "Detail":
                  if (reader.HasAttributes)
                  {
                        reader.MoveToFirstAttribute();
                        if (reader.Name.Equals("Type"))
                        {
                            m_DetailList.Add(reader.Value); //to get Detail1
                        }
                        reader.MoveToElement();
                  }
                  
                  m_DetailList.Add(reader.ReadElementString()); //read Detail text                                               break;
      }
        }
}

 

by: dualsoulPosted on 2005-01-26 at 12:26:38ID: 13146217

hm...it sounds not very clear to me...
but i'll try to explain.  

This is so called pull model. You ask XmlReader to read something - and it reads. It never read something itself - you have all the control. If you want you read, if not you skip.
 
When you call Read(), ReadString() and so on - you read something, when you call Skip(), MoveTo...() - you skip content (elements or text)

Does it make the issue more clear to you? :)

 

by: NewMom2BrandonPosted on 2005-01-27 at 08:12:48ID: 13153727

Ah yes.
I wasn't expecting the ReadElementString to move the reader forward, but to only read
the contents of the text node that it contains. I think thats where my confusion came in.

So to get what I need, I changed the ReadElementString (which forwards the node to the
next element node) to a Read() and then get the value (of the text node). That
way when it continues with the while loop and reads the next node, it will be an element (instead
of the following text node, skipping the if statment.

For some reason I did think the XmlTextReader worked a little differently. Makes more
sense now whats going on.

Thanks for your help!!

 

by: dualsoulPosted on 2005-01-27 at 12:45:22ID: 13156878

you are welcome :)

20120131-EE-VQP-002

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