listbox auto scroll down

Question

I have a listbox and checkbox, Now I want is If I click the checkbox name scroll down the listbox well be scroll down automatically with a normal speed, not to fast and not to slow.

I have a sample code:

private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
			timer2.Start();//start scroll
		}

In this code I tried to use timer_tick.

private void timer2_Tick(object sender, EventArgs e)
        {
            if (checkBox1.Checked == true)
            {
                listBox1.SelectedIndex = listBox1.Items.Count - 1;
            }
        }

The problem of this code is can scroll in listbox but supper fast.

I already check the interval of timer but still not working properly.

Please someone can help me to fix my problem. Thank you so much in advance.

Answer 1

Try to replace listBox1.SelectedIndex = listBox1.Items.Count - 1 with ++listBox1.TopIndex;

You can also stop the timer and uncheck the checkbox programmatically if there are no more items to scroll.

Answer 2

You can do something like this :

        private const int WM_VSCROLL = 0x0115;
        private const int SB_LINEUP = 0;     
        private const int SB_LINEDOWN = 1;    
        private System.Windows.Forms.Timer scrollTimer;
        private int nSrollSteps = 0;
        private int nTotalSteps = 0;

        [DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        public static extern int SendMessage(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);

{
    scrollTimer = new System.Windows.Forms.Timer();
    scrollTimer.Interval = 100;
    scrollTimer.Tick += ScrollStep;
    nTotalSteps =  listBox1.Items.Count - listBox1.ClientSize.Height / listBox1.ItemHeight;
    nSrollSteps = 0;
    scrollTimer.Start();
}

        private void ScrollStep(object sender, EventArgs e)
        {
            if (nSrollSteps < nTotalSteps)
            {
                SendMessage(listBox1.Handle, WM_VSCROLL, (IntPtr)SB_LINEDOWN, IntPtr.Zero);
                nSrollSteps++;
            }
            else
            {
                Console.Beep(5000, 10);
                scrollTimer.Stop();
            }
        }