In the previous lesson, we saw how you could position controls visually or manually. In some cases, you end up with one control positioned on top of another. Of course the first remedy that comes in mind would consist of moving one of the controls away from the other. This would also imply sometimes that you would have to enlarge and/or heighten the controls' container. There are situations that either you don't want to resize the parent or you can't: your only solution is to have one control on top of another. Fortunately, you can cope with this situation by specifying, when needed, what control at what time should be displayed to the user.

When one control is positioned on top of another, they use a third axis whose origin, like that or the other axes, is on the top-left corner of the parent. This third axis, also considered the z-axis, is oriented so that it moves from the monitor towards the user. The operating system is in charge of positioning and drawing the objects on the screen. You as the programmer can direct the operating system as to what object should be on top and what object should be behind. To support these changes the Control class uses two methods that its appropriate children derive also.

When a control A is positioned behind a control be, this causes control be either partially or completely hidden. If you want the control A to change its z-order and become on top of control B, you can call its BringToFront() method. The syntax of this method is:

Public Sub BringToFront()

On the other hand, if a control B is positioned on top of a control A, if you want control B to become positioned behind control A, you can call control B's SendToBack() method. Its syntax is:

Public Sub SendToBack()

After the controls have been positioned, at any time, when you access a control, if you want to know whether that control is the most top object, you can call its GetTopLevel() method. Its syntax is:

Protected Function GetTopLevel As Boolean