Below is the code that implements custom vertical scrollbar. The important detail here is to know when scrollbar is needed by calculating how much space is consumed by the controls that you add to the panel.
panelUserInput.SuspendLayout();
panelUserInput.Controls.Clear();
panelUserInput.AutoScroll = false;
panelUserInput.VerticalScroll.Visible = false;
// here you'd be adding controls
int x = 20, y = 20, height = 0;
for (int inx = 0; inx < numControls; inx++ )
{
// this example uses textbox control
TextBox txt = new TextBox();
txt.Location = new System.Drawing.Point(x, y);
// add whatever details you need for this control
// before adding it to the panel
panelUserInput.Controls.Add(txt);
height = y + txt.Height;
y += 25;
}
if (height > panelUserInput.Height)
{
VScrollBar bar = new VScrollBar();
bar.Dock = DockStyle.Right;
bar.Scroll += (sender, e) => { panelUserInput.VerticalScroll.Value = bar.Value; };
bar.Top = 0;
bar.Left = panelUserInput.Width - bar.Width;
bar.Height = panelUserInput.Height;
bar.Visible = true;
panelUserInput.Controls.Add(bar);
}
panelUserInput.ResumeLayout();
// then update the form
this.PerformLayout();