Better algorithm to fade a winform

Question

While searching for code to fade a winform, I came across this page on the MSDN forum.

for (double i = 0; i < 1; i+=0.01)
{
    this.Opacity = i;
    Application.DoEvents();
    System.Threading.Thread.Sleep(0);
}

The for loop has a non-integer increment and, from a previous question I asked, that's not a good programming technique (due to inexact representation of most decimals).

I came up with this alternative.

for (double i = 0; i < 100; ++i)
{
    this.Opacity = i/100;
    Application.DoEvents();
    System.Threading.Thread.Sleep(0);
}

Which of these is more efficient?

If there's a better algorithm for fading a form, I'll be very glad if it is included.

Thanks.

Answer 1

Forget timers (pun intended).

With Visual Studio 4.5 or higher, you can just await a task that is delayed. An advantage of this method is that it's asynchronous, unlike a thread Sleep or DoEvents loop, which blocks the application during the fade (and the other aforementioned DoEvents problems).

private async void FadeIn(Form o, int interval = 80) 
{
    //Object is not fully invisible. Fade it in
    while (o.Opacity < 1.0)
    {
        await Task.Delay(interval);
        o.Opacity += 0.05;
    }
    o.Opacity = 1; //make fully visible       
}

private async void FadeOut(Form o, int interval = 80)
{
    //Object is fully visible. Fade it out
    while (o.Opacity > 0.0)
    {
        await Task.Delay(interval);
        o.Opacity -= 0.05;
    }
    o.Opacity = 0; //make fully invisible       
}

Usage:

private void button1_Click(object sender, EventArgs e)
{
    FadeOut(this, 100);
}

You should check if the object is disposed before you apply any transparency to it. I used a form as the object, but you can pass any object that supports transparency as long as it's cast properly.