Asynchronous File Copy/Move in C#

Question

What is the correct way to do file copy/move asynchronously in C#?

Answer 1

There's a good article on MSDN regarding Asynchronous I/O. They have a code sample that compares doing the same thing async vs sync.

Answer 2

The correct way to copy: use a separate thread.

Here's how you might be doing it (synchronously):

//.. [code]
doFileCopy();
// .. [more code]

Here's how to do it asynchronously:

// .. [code]
new System.Threading.Thread(doFileCopy).Start();
// .. [more code]

This is a very naive way to do things. Done well, the solution would include some event/delegate method to report the status of the file copy, and notify important events like failure, completion etc.

cheers, jrh

Answer 3

You can use asynchronous delegates

public class AsyncFileCopier
    {
        public delegate void FileCopyDelegate(string sourceFile, string destFile);

        public static void AsynFileCopy(string sourceFile, string destFile)
        {
            FileCopyDelegate del = new FileCopyDelegate(FileCopy);
            IAsyncResult result = del.BeginInvoke(sourceFile, destFile, CallBackAfterFileCopied, null);
        }

        public static void FileCopy(string sourceFile, string destFile)
        { 
            // Code to copy the file
        }

        public static void CallBackAfterFileCopied(IAsyncResult result)
        {
            // Code to be run after file copy is done
        }
    }

You can call it as:

AsyncFileCopier.AsynFileCopy("abc.txt", "xyz.txt");

This link tells you the different techniques of asyn coding

Answer 4

You can do it as this article suggested:

public static void CopyStreamToStream(
    Stream source, Stream destination,
    Action<Stream, Stream, Exception> completed)
    {
        byte[] buffer = new byte[0x1000];
        AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(null);

        Action<Exception> done = e =>
        {
            if(completed != null) asyncOp.Post(delegate
                {
                    completed(source, destination, e);
                }, null);
        };

        AsyncCallback rc = null;
        rc = readResult =>
        {
            try
            {
                int read = source.EndRead(readResult);
                if(read > 0)
                {
                    destination.BeginWrite(buffer, 0, read, writeResult =>
                    {
                        try
                        {
                            destination.EndWrite(writeResult);
                            source.BeginRead(
                                buffer, 0, buffer.Length, rc, null);
                        }
                        catch(Exception exc) { done(exc); }
                    }, null);
                }
                else done(null);
            }
            catch(Exception exc) { done(exc); }
        };

        source.BeginRead(buffer, 0, buffer.Length, rc, null);

Answer 5

You could use a Backgroundworker to do it.

Here's a Windows forms sample (credit goes to "nobugz" on the msdn forums)

http://social.msdn.microsoft.com/Forums/en-US/Vsexpressvcs/thread/a285bdb9-6838-48f3-b8ed-1bf0156f8c51

Start a new project and drop a label, button and progressbar on the form. Make sure c:\temp folder exists. Then paste this code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Forms;
using System.IO;

namespace WindowsApplication1 {
  public partial class Form1 : Form {
    // Class to report progress
    private class UIProgress {
      public UIProgress(string name_, long bytes_, long maxbytes_) {
        name = name_; bytes = bytes_; maxbytes = maxbytes_;
      }
      public string name;
      public long bytes;
      public long maxbytes;
    }
    // Class to report exception {
    private class UIError {
      public UIError(Exception ex, string path_) {
        msg = ex.Message; path = path_; result = DialogResult.Cancel;
      }
      public string msg;
      public string path;
      public DialogResult result;
    }
    private BackgroundWorker mCopier;
    private delegate void ProgressChanged(UIProgress info);
    private delegate void CopyError(UIError err);
    private ProgressChanged OnChange;
    private CopyError OnError;

    public Form1() {
      InitializeComponent();
      mCopier = new BackgroundWorker();
      mCopier.DoWork += Copier_DoWork;
      mCopier.RunWorkerCompleted += Copier_RunWorkerCompleted;
      mCopier.WorkerSupportsCancellation = true;
      OnChange += Copier_ProgressChanged;
      OnError += Copier_Error;
      button1.Click += button1_Click;
      ChangeUI(false);
    }

    private void Copier_DoWork(object sender, DoWorkEventArgs e) {
      // Create list of files to copy
      string[] theExtensions = { "*.jpg", "*.jpeg", "*.bmp", "*.png", "*.gif" };
      List<FileInfo> files = new List<FileInfo>();
      string path = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
      DirectoryInfo dir = new DirectoryInfo(path);
      long maxbytes = 0;
      foreach (string ext in theExtensions) {
        FileInfo[] folder = dir.GetFiles(ext, SearchOption.AllDirectories);
        foreach (FileInfo file in folder) {
          if ((file.Attributes & FileAttributes.Directory) != 0) continue;
          files.Add(file);
          maxbytes += file.Length;
        }
      }
      // Copy files
      long bytes = 0;
      foreach (FileInfo file in files) {
        try {
          this.BeginInvoke(OnChange, new object[] { new UIProgress(file.Name, bytes, maxbytes) });
          File.Copy(file.FullName, @"c:\temp\" + file.Name, true);
        }
        catch (Exception ex) {
          UIError err = new UIError(ex, file.FullName);
          this.Invoke(OnError, new object[] { err });
          if (err.result == DialogResult.Cancel) break;
        }
        bytes += file.Length;
      }
    }
    private void Copier_ProgressChanged(UIProgress info) {
      // Update progress
      progressBar1.Value = (int)(100.0 * info.bytes / info.maxbytes);
      label1.Text = "Copying " + info.name;
    }
    private void Copier_Error(UIError err) {
      // Error handler
      string msg = string.Format("Error copying file {0}\n{1}\nClick OK to continue copying files", err.path, err.msg);
      err.result = MessageBox.Show(msg, "Copy error", MessageBoxButtons.OKCancel, MessageBoxIcon.Exclamation);
    }
    private void Copier_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) {
      // Operation completed, update UI
      ChangeUI(false);
    }
    private void ChangeUI(bool docopy) {
      label1.Visible = docopy;
      progressBar1.Visible = docopy;
      button1.Text = docopy ? "Cancel" : "Copy";
      label1.Text = "Starting copy...";
      progressBar1.Value = 0;
    }
    private void button1_Click(object sender, EventArgs e) {
      bool docopy = button1.Text == "Copy";
      ChangeUI(docopy);
      if (docopy) mCopier.RunWorkerAsync();
      else mCopier.CancelAsync();
    }
  }
}