Resize TableLayoutPanel when adjacent control is resized

This works perfectly with two panels - one for the top, with DockStyle.Top, and the "main" one with DockStyle.Fill.

You could try wrapping your custom control in a panel and experiment with anchoring or Fill'ing, if it doesn't dock properly to the top.

var form = new Form();

var shrinking = new Panel() 
{
    BackColor = Color.Red,
    Dock = DockStyle.Top
};
var filling = new TableLayoutPanel()
{
    BackColor = Color.Green,
    Dock = DockStyle.Fill
};

var timer = new System.Windows.Forms.Timer();
timer.Interval = 500;
timer.Tick += (s, a) =>
{
    shrinking.Height -= 10;
    if(shrinking.Height <= 0) {
        shrinking.Height = 0;
        timer.Stop();
    }
};

form.Shown += (s, a) => timer.Start();


// Just to make sure it works with a menu present   
var menu = new MenuStrip();
menu.Items.Add("&File");    

form.Controls.Add(shrinking);   
form.Controls.Add(filling); 
form.Controls.Add(menu);
form.ShowDialog();