follow loading progress of huge XML files

Question

I try to follow the loading progress of big XML files (I\'m not the provider of these files) in dotnet (C#, framework 3.5 SP1) : from 1 MB to 300 MB over a network file shar

Answer 1

With the inbuilt loaders there isn't much; you could, however, write an intercepting stream - load your document from this stream, and expose the Position via events? i.e. raise an event in the Read method (at intervals)?

---

Here's an example that supports updates during both read and write:

using System;
using System.IO;
using System.Xml;
class ChattyStream : Stream
{
    private Stream baseStream;
    public ChattyStream(Stream baseStream)
    {
        if (baseStream == null) throw new ArgumentNullException("baseStream");
        this.baseStream = baseStream;
        updateInterval = 1000;
    }
    public event EventHandler ProgressChanged;
    protected virtual void OnProgressChanged()
    {
        var handler = ProgressChanged;
        if (handler != null) handler(this, EventArgs.Empty);
    }
    private void CheckDisposed()
    {
        if (baseStream == null) throw new ObjectDisposedException(GetType().Name);
    }
    protected Stream BaseStream
    {
        get { CheckDisposed(); return baseStream; }
    }
    int pos, updateInterval;
    public int UpdateInterval
    {
        get { return updateInterval; }
        set
        {
            if (value <= 0) throw new ArgumentOutOfRangeException("value");
            updateInterval = value;
        }
    }

    protected void Increment(int value)
    {
        if (value > 0)
        {
            pos += value;
            if (pos >= updateInterval)
            {
                OnProgressChanged();
                pos = pos % updateInterval;
            }
        }
    }
    public override int Read(byte[] buffer, int offset, int count)
    {
        int result = BaseStream.Read(buffer, offset, count);
        Increment(result);
        return result;
    }
    public override void Write(byte[] buffer, int offset, int count)
    {
        BaseStream.Write(buffer, offset, count);
        Increment(count);
    }
    public override void SetLength(long value)
    {
        BaseStream.SetLength(value);
    }
    public override void Flush()
    {
        BaseStream.Flush();
    }
    public override long Position
    {
        get { return BaseStream.Position; }
        set { BaseStream.Position = value; }
    }
    public override long Seek(long offset, SeekOrigin origin)
    {
        return BaseStream.Seek(offset, origin);
    }
    public override long Length
    {
        get { return BaseStream.Length; }
    }
    public override bool CanWrite
    {
        get { return BaseStream.CanWrite; }
    }
    public override bool CanRead
    {
        get { return BaseStream.CanRead; }
    }
    public override bool CanSeek
    {
        get { return BaseStream.CanSeek; }
    }
    protected override void Dispose(bool disposing)
    {
        if (disposing && baseStream != null)
        {
            baseStream.Dispose();
        }
        baseStream = null;
        base.Dispose(disposing);
    }
    public override void Close()
    {
        if (baseStream != null) baseStream.Close();
        base.Close();
    }
    public override int ReadByte()
    {
        int val = BaseStream.ReadByte();
        if (val >= 0) Increment(1);
        return val;
    }
    public override void WriteByte(byte value)
    {
        BaseStream.WriteByte(value);
        Increment(1);
    }

}
static class Program
{
    static void Main()
    {
        /* invent some big data */
        const string path = "bigfile";
        if (File.Exists(path)) File.Delete(path);
        using (var chatty = new ChattyStream(File.Create(path)))
        {
            chatty.ProgressChanged += delegate
            {
                Console.WriteLine("Writing: " + chatty.Position);
            };
            using (var writer = XmlWriter.Create(chatty))
            {
                writer.WriteStartDocument();
                writer.WriteStartElement("xml");
                for (int i = 0; i < 50000; i++)
                {
                    writer.WriteElementString("add", i.ToString());
                }
                writer.WriteEndElement();
                writer.WriteEndDocument();
            }
            chatty.Close();
        }


        /* read it */

        using (var chatty = new ChattyStream(File.OpenRead("bigfile")))
        {
            chatty.ProgressChanged += delegate
            {
                Console.WriteLine("Reading: " + chatty.Position);
            };

            // now read "chatty" with **any** API; XmlReader, XmlDocument, XDocument, etc
            XmlDocument doc = new XmlDocument();
            doc.Load(chatty);
        }
    }
}