C# Changing background color of Form using Button

Question

I have a simple problem with a code from a C# book. The code is suppose to change background color every time I click the button. The problem is it changes the color to green and instantly goes back to purple again. After clicking again, the situation and colors stay the same. I think there's a problem with Application.DeEvents() because it seems that after one iteration, parameters goes back to default. This is a book's fault obviously but I wanted to make it work, anyway. I found a question about the very same code but it was about for loop and it's not said why code can't work in the first place.

    {
        for (int c = 0; c < 254 && Visible; c++)
        {
            this.BackColor = Color.FromArgb(c, 255 - c, c);
            Application.DoEvents();
            System.Threading.Thread.Sleep(5);
        }
    }
}

Why are you looping? Are you trying to do some kind of animation of the colour? — Blorgbeard
– Blorgbeard, Commented Nov 4, 2017 at 18:13
Ya, the outcome should be changing the background color of a Form every time I click the button. — Mike
– Mike, Commented Nov 4, 2017 at 18:19
You are changing the back color for every 5 milliseconds, you will not really noticing the changes in color — Abdullah Dibas
– Abdullah Dibas, Commented Nov 4, 2017 at 18:20

Olivier Jacot-Descombes · Accepted Answer · 2017-11-04 18:24:41Z

1

254 iterations last 254 * 5 ms = 1.27 seconds. So, just after clicking you get RGB(0, 255, 0) == green. Then the loop changes the color graduallly to RGB(253, 2, 253)` == purple within 1.27 seconds. It's what your code tells it to do.

Note also that 5 ms is shorter than the monitor refresh rate at 60Hz (~ 16.7 ms).

If you want to change the color gradually manually instead of automatically, remove the loop and store c in a field (outside of the method).

private int c = 0;

private void Button1_Click(object sender, EventArgs e)
{
    this.BackColor = Color.FromArgb(c, 255 - c, c);
    c = (c + 1) % 256; // 256 % 256 == 0. % = modulo operator.
}

Now, the color changes slightly at every click.

answered Nov 4, 2017 at 18:24

Olivier Jacot-Descombes

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2 Comments

Mike Over a year ago

Ok I get it, thanks. I also figured out the loop way, the author says it's an example and I shouldn't use DoEvents() in real example, it's just educational one. But I added another for loop where c goes down and after clicking the button it goes green->purple->green and stops and that's probably what the example is about. Thanks for the help, appreciate it.

Olivier Jacot-Descombes Over a year ago

Yeah, and because it's just educational one, you can tell students to do things they shouldn't do :-). In a real world example, you should use a timer instead of a loop.

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