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Editorial Team
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Asked: 2026-06-15T02:30:18+00:00

I am going through this tutorial on how to perform some work in the

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I am going through this tutorial on how to perform some work in the background and in this piece of code I am confused as to why the message reading the file... is not displayed before the ReadTheFile(filename) method is called.

private void btnSelect_Click(object sender, EventArgs e)
{
    OpenFileDialog ofd = new OpenFileDialog();
    ofd.CheckFileExists = true;
    ofd.CheckPathExists = true;

    if (ofd.ShowDialog() == DialogResult.OK)
    {
        lblResults.Text = " ... reading the file ...";
        FileReader1 fr = new FileReader1();
        int numLines = fr.ReadTheFile(ofd.FileName);

        lblResults.Text = string.Format("We read {0} lines", numLines.ToString());
    }
}

The author explains it by saying the following, but it did not really get through to me.

Worse, even though we set the label’s Text property before we call ReadTheFile, the message loop doesn’t get a chance to process that change, and update the text, before we go out to lunch in ReadTheFile.

What does this mean? Can this be explained in simpler terms?

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1 Answer

  1. Editorial Team

    Worse, even though we set the label’s Text property before we call ReadTheFile, the message loop doesn’t get a chance to process that change, and update the text, before we go out to lunch in ReadTheFile.

    Basically you are setting the text of label. However, you then start doing a “intensive” task that could take seconds, minutes, hours. As long as you are continuing to load the file and read the number of lines, the window will not update. That’s the point of doing it in a background thread. Let the main thread continue to paint the window and handle UI stuff while your background thread processes the file.

    I would continue with the tutorial. Once you get to the part where you start creating and running the background worker you may end up with one of those “Aha!” moments. =)

    You may also be interested in reading up on threads in general.

    http://www.codeproject.com/Articles/26148/Beginners-Guide-to-Threading-in-NET-Part-1-of-n

    http://www.techrepublic.com/article/a-beginners-guide-to-threading-in-c/1044970

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