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I try to create a countdown in c#, but it refreshes the Form UI every second, and this action makes a flashing issue.

i attached this video on youtube to show the issue here

UI Issue with Timer in C# - YouTube[^]

What I have tried:

I tried to use Timer also BackgroundWorker and the issue appears with all of them.

this the last code i tried:

System.Threading.Timer timer;
       private void StartTimer_Click(object sender, EventArgs e)
           timer = new System.Threading.Timer(_ => TimerTicks(), null, 0, 1000);


private void TimerTicks()
            if (selectedQuestTimer > 0)
                if (selectedQuestTimer == selectedQuestion.time)
                if (selectedQuestTimer == selectedQuestion.time - 3)
                if (selectedQuestTimer == 5)

                Invoke((MethodInvoker)(() => ChangeTimerDataData()));

            else if (selectedQuestTimer == 0)

Updated 30-Jan-23 1:06am
Maciej Los 30-Jan-23 8:24am    
What does "ChangeTimerDataData" method?
Dave Kreskowiak 30-Jan-23 9:33am    
The problem is going to be in the code your timer is calling, which you didn't show.

I can't see what your render is doing. You may need to use double buffering...

First try setting the form's DoubleBuffered property to True. Otherwise, for controls, have a read of this: c# flickering Listview on update[^]

You can make that code more generalized for all controls:
public static class ControlsExtension
    public static void SetDoubleBuffered(this Control control, bool doubleBuffered = true)
            .GetProperty("DoubleBuffered", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)
            ?.SetValue(control, doubleBuffered, null);
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Golden Basim 30-Jan-23 7:44am    
i tried this solution but still flickering the form
Graeme_Grant 30-Jan-23 9:17am    
The code posted is not the issue. Without seeing the rendering code, I can only suggest based on what is a common issue.
Ralf Meier 30-Jan-23 12:50pm    
I agree with @Grame_Grant - somewhere in your code (perhaps the Countdown-Display) forces an Invalidate of the complete Form.
Maybe System.Windows.Forms.Timer will fix your issues?
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