Can't set Label.Text

[Pelgar]

I've been working with C# for about 6 months. This is the first time that a little searching has not resolved a problem for me. I'm trying to change the text of a label and update a progress bar in a loop that does some graphic calculations. The progress bar is working fine but the label text does not change until the loop has completed.

        int nImgCnt = m\_Parent.m\_ImageList.Count - 1;
        int nStatBarAdd = 1000 / nImgCnt;

        for (int nIdx = 0; nIdx <= nImgCnt; nIdx++)
        {   //FInd Min rectangle that will contain largest image
           lblProg.Text = "Calculating minimum image size. Image " + (nIdx+1).ToString() + " of " + (nImgCnt + 1).ToString();
           lblProg.Focus();        //Tried this just to see if it would work
           lblProg.Invalidate();   //Tried this just to see if it would work
           CurRC = getImageMinSize(m\_Parent.m\_ImageList\[nIdx\]); 
            if (CurRC.Width > MinRC.Width)
            {
                MinRC.Width = CurRC.Width;
                MinRC.X = CurRC.X;
            }
            if (CurRC.Height > MinRC.Height)
            {
                MinRC.Height = CurRC.Height;
                MinRC.Y = CurRC.Y;
            }
            prgBr.Value += nStatBarAdd;

        }

If anyone can help me out with this I will really appreciate it!

[Luc Pattyn]

it all depends where your code is sitting. if it is in a GUI event handler (say a button click handler) then the main thread would be busy with your code, and hence the GUI would not respond to the things the user does, and a lot of things your code does. The right approach would be to use a separate thread, maybe a BackgroundWorker would be fine. if it is not in a GUI event handler, hence already being executed by some other thread, then you are performing illegal cross-thread operations to GUI components. You might want to read this article[^]. All the above applies to all kinds of Controls; from what I've seen, I can't tell why the progress bar works better for you, I don't think it should the way things are. :)

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[Pelgar]

Thanks for the quick response Luc! Sorry, I should have pointed out this is in a button click event handler. I will trying doing the calculations in a BackgroundWorker, thanks again! Edit: I added a BackgroundWorker and life is good again. Thanks again Luc! I should have worked this one out for myself. I must be having a bad code day.

modified on Sunday, January 2, 2011 1:47 PM

[Luc Pattyn]

You're welcome. :)

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[Jeff Connelly]

Luc Pattyn wrote:

if it is not in a GUI event handler, hence already being executed by some other thread, then you are performing illegal cross-thread operations to GUI components. You might want to read this article[^].

But since he's not getting an exception, that can't be it. Unless there's more to it than I've experienced.

[Luc Pattyn]

He didn't mention exceptions, so it was unclear whether any occurred or not. And a ThreadPool thread would happily swallow any exception he didn't handle explicitly: ThreadPool threads are built to survive no matter what. :)

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