Question

I am reading data from a file and would like to attach a progress bar to this operation. I found the following code on stackoverflow – this code is due to William Daniel, Sept 20, stackoverflow post titled, ” How to Change Color of Progress Bar in C#.Net 3.5″

class CustomProgressBar : ProgressBar
{
    public CustomProgressBar()
    {
        this.SetStyle(ControlStyles.UserPaint, true);
    }

    protected override void OnPaintBackground(PaintEventArgs pevent)
    {
        // None... Helps control the flicker.
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        const int inset = 2;
        using (Image offscreenImage = new Bitmap(this.Width, this.Height))
        {
            using (Graphics offscreen = Graphics.FromImage(offscreenImage))
            {
                Rectangle rect = new Rectangle(0, 0, this.Width, this.Height);

                if (ProgressBarRenderer.IsSupported)
                    ProgressBarRenderer.DrawHorizontalBar(offscreen, rect);

                rect.Inflate(new Size(-inset, -inset));  // Deflate inner rectangle
                rect.Width = (int)(rect.Width * ((double)this.Value / this.Maximum));
                if (rect.Width == 0) rect.Width = 1;
                LinearGradientBrush brush = new LinearGradientBrush(rect,
                      this.BackColor, this.ForeColor, LinearGradientMode.Vertical);
                offscreen.FillRectangle(brush, inset, inset, rect.Width, rect.Height);

                e.Graphics.DrawImage(offscreenImage, 0, 0);
                offscreenImage.Dispose();
            }
        }
    }
}

The code works fine except the following:

1. The gradient does not seem to extend the entire width of the bar. It is there but is much more heavily concentrated near the bottom of the bar and thins out very quickly as we get to the top of the bar. Any suggestions as to how I can fix this?

2. If I place the progress bar on a form and open an Internet Explorer window over the portion of the form with the progress bar on it, some of the text from the internet window bleeds onto the progress bar in the form. I have no idea why, and how to fix this.

As an aside, how does one estimate the length of an operation that you wish to show via a progress bar?

Any help would be greatly appreciated. Thank you.

Answer 1

As for first part of your question – try using following constructor for your brush:

new LinearGradientBrush(new Point(0, 0), new Point(0, Height - inset * 2), BackColor, ForeColor);

Your current brush has top control point at Y=inset – that’s why area from Y=0 to Y=inset is all painted in solid color.