The three built-in control classes, ProgressBar, Slider, and Scrollbar, are variations on a single theme: each provides a visual representation of a numeric value in terms of its position along a scale. They differ, however, in details of appearance and usage:
A ProgressBar displays a “thermometer,” such as might provide the user with visual feedback as to the progress of a time-consuming task.
A Slider displays a horizontal or vertical “slot” with a “knob”; the user can slide the knob along the slot, like a sliding control on a piece of audio equipment, and can click in the slot to move the knob by a fixed amount.
A Scrollbar displays a standard horizontal or vertical scrollbar, with arrows at each end and a scroll box (or thumb) between. The user can slide the thumb, click the arrows to move the thumb by a small fixed amount, or click the gray areas on either side of the thumb to move the thumb by a larger fixed amount.
The numeric values for these controls must lie between
32767. This is
because, owing to the way they are implemented by the Macintosh
Toolbox, the value is actually a short integer (two bytes).
A ProgressBar, Slider, or Scrollbar is a RectControl, and therefore receives all the events and has all the methods and properties listed in Chapter 10: Open and Close events; Visible, Enabled, and AutoDeactivate properties; Top, Left, Height, and Width properties; LockLeft, LockRight, LockTop, and LockBottom ...