Animation effect by changing colors

[Razanust]

I have written a code to change the back color of a label twice during execution to give it an animation effect. The idea says that :

when the button is pressed change the color from black to red.
Then a null loop is placed to create some delay and then the color changes back to black.

<pre lang="vb">Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
box.BackColor = Color.Red
For delay As Double = 0 To 900000000 Step 1
Next
box.BackColor = Color.Black
End Sub</pre>

But its not performing as desired. The label doesnt become red and i doubt the program is executing the delay first. Any idea whats the issue?

[Wayne Gaylard]

You will need to change the colour back using a separate thread. Something like this:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim newThread As New Threading.Thread(New Threading.ThreadStart(AddressOf ChangeBGColour))
newThread.Start()
Label1.BackColor = Color.Red

End Sub

Private Sub ChangeBGColour()

Threading.Thread.Sleep(3000) 'adjust time as necessary
Label1.BackColor = Color.Yellow

End Sub

Hope this helps

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modified on Tuesday, August 30, 2011 3:31 AM

[Dave Kreskowiak]

You're getting downvoted because you cannot touch a UI control from any other thread other than the thread that created it (the startup thread.)

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Dave Kreskowiak

[Dave Kreskowiak]

Your code is running on the startup thread, also called UI thread. If the thread is blocked there is no way it can process the Windows PAINT messages that tell the controls to repaint themselves. This is why your label doesn't change color until your button Click method is done executing. You have to move your work to a background thread. The problem is you cannot make changes to a control, such as changing the background color, from anything other that the UI thread. Once your background thead "work" is done the background thread can notify the foreground thread to change the label color as appropriate. Read this article[^] for a discussion and alternate methods of modifying controls from background threads.

A guide to posting questions on CodeProject[^]
Dave Kreskowiak

[Luc Pattyn]

:thumbsup:

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[Wayne Gaylard]

You will need to change the colour back using a separate thread. Something like this:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

    Dim newThread As New Threading.Thread(New Threading.ThreadStart(AddressOf ChangeBGColour))
    newThread.Start()
    Label1.BackColor = Color.Red

End Sub

Delegate Sub changeLabelColour()

Private Sub ChangeBGColour()

    Threading.Thread.Sleep(3000)
    If Me.Label1.InvokeRequired Then
        Dim c As New changeLabelColour(AddressOf ChangeBGColour)
        Me.Invoke(c)
    Else
        Label1.BackColor = Color.Yellow
    End If

End Sub

I added proper UI thread access . My apologies for the basic thread error. Hope this helps

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[Wayne Gaylard]

Thanks, very elementary mistake. Note to self, think before posting. I have corrected the answer below(first one was removed).

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[Dalek Dave]

That's an excellent answer.

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[Wayne Gaylard]

Cheers.

Live for today. Plan for tomorrow. Party tonight!