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Posted 8 Aug 2006

Simplify Reading and Writing of XML Fragments

, 8 Aug 2006
This article shows how to read and write XML fragments using the XmlChunkReader and XmlChunkWriter classes.
/* Copyright (c) 2006 notmasteryet */
using System;
using System.Xml;

namespace XmlChunk
{
    /// <summary>
    /// XmlChunkWriter can be created using XmlWriter. It can be used 
    /// as standalone XmlWriter, e.g. to perform serialization of the 
    /// objects. When XmlChunkWriter is closed, main XmlWriter is ready 
    /// to continue write XML data. Using of XmlChunkWriter helps format 
    /// data is same manner and avoid writing of xml declaration 
    /// instruction in the middle of XML.
    /// </summary>
    public class XmlChunkWriter : XmlWriter
    {
        private const string XmlnsPrefix = "xmlns";
        private const string XmlnsXsiName = "xsi";
        private const string XmlnsXsdName = "xsd";

        private XmlWriter baseWriter;
        private bool skipXsiNsAttributes;
        private int depth;
        private State state;

        /// <summary>
        /// Contains base XmlWriter
        /// </summary>
        public XmlWriter BaseWriter
        {
            get 
            {
                if (state == State.Completed)
                    throw new InvalidOperationException(Properties.Resources.WriterIsClosed);
                
                return baseWriter; 
            }
        }

        /// <summary>
        /// Creates writer
        /// </summary>
        /// <param name="writer">Base writer</param>
        public XmlChunkWriter(XmlWriter writer) : this(writer, true)
        {
        }

        /// <summary>
        /// Creates writer
        /// </summary>
        /// <param name="writer">Base writer</param>
        /// <param name="skipXsiNsAttributes">Root xmlns:xsi and xmlns:xsd attributes will be removed if true</param>
        public XmlChunkWriter(XmlWriter writer, bool skipXsiNsAttributes)
        {
            if (writer == null)
                throw new ArgumentNullException("writer");

            this.baseWriter = writer;
            this.skipXsiNsAttributes = skipXsiNsAttributes;
            this.depth = 0;
            this.state = State.Idle;
        }

        public override void Close()
        {
            BaseWriter.Flush();
            state = State.Completed;
        }

        public override void Flush()
        {
            BaseWriter.Flush();
        }

        public override string LookupPrefix(string ns)
        {
            return BaseWriter.LookupPrefix(ns);
        }

        public override void WriteBase64(byte[] buffer, int index, int count)
        {
            BaseWriter.WriteBase64(buffer, index, count);
        }

        public override void WriteCData(string text)
        {            
            BaseWriter.WriteCData(text);
        }

        public override void WriteCharEntity(char ch)
        {
            if (state == State.SkipAttribute) return;
            BaseWriter.WriteCharEntity(ch);
        }

        public override void WriteChars(char[] buffer, int index, int count)
        {
            if (state == State.SkipAttribute) return;
            BaseWriter.WriteChars(buffer, index, count);
        }

        public override void WriteComment(string text)
        {
            BaseWriter.WriteComment(text);
        }

        public override void WriteDocType(string name, string pubid, string sysid, string subset)
        {            
        }

        public override void WriteEndAttribute()
        {
            if (state != State.SkipAttribute)
            {
                BaseWriter.WriteEndAttribute();
            }
            else
                state = State.InProcess;
        }

        public override void WriteEndDocument()
        {            
        }

        public override void WriteEndElement()
        {
            BaseWriter.WriteEndElement();
            --depth;
        }

        public override void WriteEntityRef(string name)
        {
            if (state == State.SkipAttribute) return;
            BaseWriter.WriteEntityRef(name);
        }

        public override void WriteFullEndElement()
        {
            BaseWriter.WriteFullEndElement();
            --depth;
        }

        public override void WriteProcessingInstruction(string name, string text)
        {
            BaseWriter.WriteProcessingInstruction(name, text);
        }

        public override void WriteRaw(string data)
        {
            BaseWriter.WriteRaw(data);
        }

        public override void WriteRaw(char[] buffer, int index, int count)
        {
            BaseWriter.WriteRaw(buffer, index, count);
        }

        protected virtual bool IsXsiAttribute(string prefix, string localName, string ns)
        {
            return prefix == XmlnsPrefix && 
                (localName == XmlnsXsiName || localName == XmlnsXsdName);
        }

        public override void WriteStartAttribute(string prefix, string localName, string ns)
        {
            if (depth == 1 && skipXsiNsAttributes && IsXsiAttribute(prefix ,localName, ns))
            {
                // skiping attribute with namespace definition in root node
                state = State.SkipAttribute;
                return;
            }

            BaseWriter.WriteStartAttribute(prefix, localName, ns);
        }

        public override void WriteStartDocument(bool standalone)
        {
        }

        public override void WriteStartDocument()
        {
        }

        public override void WriteStartElement(string prefix, string localName, string ns)
        {
            BaseWriter.WriteStartElement(prefix, localName, ns);
            state = State.InProcess;
            ++depth;
        }

        public override WriteState WriteState
        {
            get 
            { 
                switch(state)
                {
                    case State.Idle:
                        return WriteState.Start;
                    default:
                    case State.InProcess:
                        return BaseWriter.WriteState;
                    case State.SkipAttribute:
                        return WriteState.Attribute;
                    case State.Completed:
                        return WriteState.Closed;
                }
            }
        }

        public override void WriteString(string text)
        {
            if (state == State.SkipAttribute) return;
            BaseWriter.WriteString(text);
        }

        public override void WriteSurrogateCharEntity(char lowChar, char highChar)
        {
            if (state == State.SkipAttribute) return;
            BaseWriter.WriteSurrogateCharEntity(lowChar, highChar);
        }

        public override void WriteWhitespace(string ws)
        {
            BaseWriter.WriteWhitespace(ws);
        }

        private enum State
        {
            Idle,
            InProcess,
            SkipAttribute,
            Completed
        }
    }
}

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About the Author

notmasteryet
Software Developer
United States United States
No Biography provided

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