Question

I have a custom control’s library. Now there’s a control which looks like a panel, and when it opens up I want to animate its vertical growing like this:

For h As Single = 0 To finalHeight Step 0.5
    Me.Height = CInt(h)
    '  HERE I WANT TO CALL DoEvents'
Next
Me.Height = finalHeight 

If I don’t call DoEvents in the loop then the animation is not shown, I only get the final height without a visual feedback along the way.

I can call DoEvents from inside my main WinForm project, but can’t inside a library.

How can I do that, without drowning into the deep threads waters?

Answer 1

This is what I’ve found: the timer, even at fast intervals, it is really slow. I don’t know why but the animation is very jumpy with the timer. Simplified code:

 rolex = New Timer()
 rolex.Interval = 150
 AddHandler rolex.Tick,
            Sub(sender As Object, e As EventArgs)

                Me.Height += 5

                If Me.Height < finalHeight Then Exit Sub

                rolex.Stop()
                rolex = Nothing

                Me.Height = finalHeight 
            End Sub
 rolex.Start()

Without the timer I use a loop:

For i As Single = 0 To finalHeight Step 0.5
            Height = CInt(i)
            Application.DoEvents()
Next
Height = finalHeight 

It works now, but the problem is that the animation speed too much depends on the machine where the loop is executed. For this reason I’d like to use a Timer, but as I said it’s too slow.

Any hints?