I have a form, and in design mode, I want to plunk down a bunch of custom
controls onto it, and set their properties.  Then, when the application runs,
I want to do something to each of the custom controls.

What I actually have is a bunch of custom buttons for a machine control
panel.  Each button is implemented as a custom control, an instance of the
MachineButton class.  It has an OnOff property, with a boolean value.  True =
0n, False = off.  I  want to do this without having to manually code a list
of MachineButtons, adding each new button created into it via code.  To make
it work, I have to be able to find out what sort of control something is.

What I want to do is have a function that turns all the buttons off.  The
pseudocode would look like this:

class MachineButton:control
{
   //insert definition of MachineButton here.  It's a custom control.

  private bool varOnOff;  //There's an OnOff property
  public bool OnOff
{
get {return varOnOff;} set {varOnOff=value}

}

public void TurnOnAllTheButtons(bool newstate)
{
    foreach (Control c in controls)
{    if (c is a MachineButton)
    { MachineButton mb=(MachineButton)c;
      mb.OnOff=false;
   }
}
}

Is there a way to write the (c is a MachineButton) test?