Using BackgroundWorker in Windows Forms Application

Download Demo - Download Project

I created a simple Windows Forms project using C# while taking advantage of BackgroundWorker object to run task at backward thread.

You just have to change/alter only one method: "CallMeBackward" which is called at backward thread in the demo project.

using System;
using System.ComponentModel;
using System.Threading;

namespace BackgroundWorkerInWindowsFormsApp
{
    public partial class Form1 : System.Windows.Forms.Form
    {
        BackgroundWorker _backgroundWorker = new BackgroundWorker();
        
        /*============================================================================*/
        public Form1()
        {
            InitializeComponent();
            
            /*============================================================================*/
            _backgroundWorker.DoWork += new DoWorkEventHandler(BackgroundWorkerDoWorkEvent);
            _backgroundWorker.WorkerSupportsCancellation = true;

            ThreadPool.QueueUserWorkItem(_backgroundWorker.RunWorkerAsync);
            /*============================================================================*/
        }

        /*============================================================================*/
        void BackgroundWorkerDoWorkEvent(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker backgroundWorker = sender as BackgroundWorker;
            string argument = (string)e.Argument;
            e.Result = OnTimeConsumingOperation(backgroundWorker, argument);
        }
        /*============================================================================*/
        string OnTimeConsumingOperation(BackgroundWorker bw, string arg)
        {
            ThreadPool.QueueUserWorkItem(_ =>
            {
                CallMeBackward();
            });
            return string.Empty;
        }
        /*============================================================================*/
        void CallMeBackward()
        {
            for (var i = 0; i < 2000; i++)
            {
                counterLabel.Text = i.ToString();
                timerLabel.Text = DateTime.Now.ToLongTimeString();
            }
        }
        /*============================================================================*/
        protected override void Dispose(bool disposing)
        {
            _backgroundWorker.CancelAsync();
            _backgroundWorker.Dispose();
            /*============================================================================*/
            var timer = new System.Windows.Forms.Timer();
            timer.Tick += (obj, evt) =>
            {
                if (!_backgroundWorker.IsBusy)
                {
                    if (disposing && (components != null))
                    {
                        components.Dispose();
                    }
                    base.Dispose(disposing);
                }
            };
            timer.Start();            
        }

        /*============================================================================*/        
    }
}

UI elements are not thread-safe and should be accessed only on the thread that created them. Otherwise you'll get following error message:

Cross-thread operation not valid: Control 'richTextBox1' accessed from a thread other than the thread it was created on.

BackgroundWorker cannot intercept main thread for UI elements. You've to use main thread instead.

C# and wiki markup parsing

Wiki Markup is the syntax or keyword used by wiki websites to format a webpage. You can use *asterisks* around a word for bold and _underscore_ for italic and this is common and easy to adopt.

Examples:

• _italic_ or {{italic}}
• *bold* or ((bold))

Wikipedia is using a different style of wiki markup and Google project hosting (as well as Google+) is using the same wiki markup I demonstrated above.

Implementation in C#
I am using Regex to implement wiki markup in C#.

And here is the method that does the entire job required for parsing any kind of wiki markup.

private static string ReplaceWikiMarkup(this string inputString, IList<string> pairs,
                                        IList<string> startTag, IList<string> endTag)
{
    for (var i = 0; i < pairs.Count; i++)
    {
        var r = new Regex(pairs[i] + "(.*?)" + pairs[i]);
        var matches = r.Matches(inputString);
        for (var j = 0; j < matches.Count; j++)
        {
            inputString = inputString.Replace(matches[j].Groups[0].Value,
                                                      startTag[i] +
                                                            matches[j].Groups[1].Value.Trim() +
                                                      endTag[i]);
        }
    }
    return inputString;
}

Using (calling) above method:

public static string ReplaceWikiMarkup(this string inputString)
{
    inputString = inputString.Replace("*", "-b-"); /* becasue asterisk(*) is a reserved word in Regex */
    return inputString.ReplaceWikiMarkup(
                new[] { "-b-", "_" },
                new[] { "<b>", "<i>" },        /* SEO: use <strong> instead */
                new[] { "</b>", "</i>" });
}

Understanding the method 
There are 4 arguments we are passing to the method:

• inputString - Input in any format
• pairs - Wiki Markup syntax or keywords: *Asterisk*, _underscore_ or anything else you use
• startTag - This can be HTML element’s empty starting tag or stating tag with any number of attributes Examples: <b><i><strong><h2 class="something"><pre style="something: something ;">
  
• endTag - This is the ending tag of HTML element Examples: </b></i></strong></h2></pre>
  

You must be careful for the ordering of HTML elements for startTag and endTag parameters. I mean that if startTag’s first element is <b> then endTag’s first element must be </b> and so on. Heading: Extending the method Let us assume that you want to use {{{ }}} or <code></code> as wiki markup for letting end-user inject the code.

• Code: {{{ --- }}} or <code> --- </code>
• Heading: [[ Heading ]]
• Bold: (( Bold ))

public static string ReplaceWikiMarkup(this string inputString, 
                                IList<string> startKeywords, /* {{{ or <code> or <h> */
                                IList<string> endKeywords,   /* }}} or </code> or </h> */
                                IList<string> startTag,      /* HTML equivalent starting tag */
                                IList<string> endTag)        /* HTML equivalent ending tag */
{
    for (var i = 0; i < startKeywords.Count; i++)
    {
        var r = new Regex(startKeywords[i] + "(.*?)" + endKeywords[i]);
        var matches = r.Matches(inputString);
        for (var j = 0; j < matches.Count; j++)
        {
            inputString = inputString.Replace(matches[j].Groups[0].Value,
                                                      startTag[i] + matches[j].Groups[1].Value.Trim() +
                                                      endTag[i]);
        }
    }
    return inputString;
}

And now we are ready to call above (changed) method:

public static string ReplaceWikiMarkup(this string inputString)
{
    inputString = inputString.Replace("*", "-b-");
    return inputString.Replace(
                new[] { "-b-", "_", "<h>", "<code>" },
                new[] { "-b-", "_", "</h>", "</code>" },
                new[] { "<b>", "<i>", "<h2>", "<pre>" },
                new[] { "</b>", "</i>", "</h2>", "</pre>" });
}