In the standard system, the KeyDown, KeyUp and KeyPress events do not respond to the tab key.To detect this key you need to override the ProcessCmdKey method that is defined for all forms control.
Please have a look on that
protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
base.ProcessCmdKey(ref msg, keyData);
if (keyData == Keys.Tab)
{
string value = keyData.ToString();
return true;
}
return false;
}
In this case if you press tab you will get the string value "Tab"