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algorithm. (Z-ordering is what Windows uses to decide where it displays a new window on
the screen. If the new window does not have specific placement information, it will be
displayed just below and to the right of the last window displayed on the screen.) The
poScreenCenter option causes the form to be displayed in the center of the screen each time
it is shown.
Visible
The Visible property controls whether the form is initially visible. This property is not
particularly useful at design time, but at runtime it can be read to determine whether the form
is currently visible. It can also be used to hide or display the form.
WindowState
The WindowState property can be read to determine the form’s current state (maximized,
minimized, or normal). It can also be used to indicate how the form should initially be
displayed. Choices are wsMinimized, wsMaximized, and wsNormal.
Runtime-Only Properties
Some properties can be accessed only at runtime through code. The following are the most
commonly used runtime properties.
ActiveMDIChild
When read, the ActiveMDIChild property returns a pointer to the currently active MDI child
window. This property is read-only.
Canvas
The form’s canvas represents the drawing surface of the form. The Canvas property gives you
access to the form’s canvas. By using the Canvas property you can draw bitmaps, lines, shapes,
or text on the form at runtime. Most of the time you will use a Label component to draw text
on a form, an Image component to display graphics, and a Shape component to draw shapes.
However, there are times when you need to draw on the canvas at runtime and the Canvas
property allows you to do that. The Canvas property can also be used to save an image of the
form to disk.
ClientRect
The ClientRect property contains the top, left, right, and bottom coordinates of the client
area of the form. This is useful in a variety of programming situations. For instance, you may
need to know the client area’s width and height in order to place a bitmap on the center of
the form.