Scroll Event 37

Applies To: Scroll, TrackBar

Description

If enabled, this event is generated when the user attempts to move the thumb in a scrollbar. This can be done in one of three ways:

1. dragging the thumb.
2. clicking in one of the "arrow" buttons situated at the ends of the scrollbar. This is termed a small change, the size of which is defined by Step[1].
3. clicking in the body of the scrollbar. This is termed a large change, the size of which is defined by Step[2].

The event message reported as the result of ⎕DQ, or supplied as the right argument to your callback function, is a 4-element vector as follows :

[1]	Object	ref or character vector
[2]	Event	'Scroll' or 37
[3]	Scroll Type	numeric
[4]	Position	numeric

The value of Scroll Type is 0 (drag), 1 or ¯1 (small change) or 2 or ¯2 (large change). The sign indicates the direction.

The value of Position is the new (requested) position of the thumb. Notice however, that the event is generated before the thumb is actually moved. If your callback function returns a scalar 0, the position of the thumb will remain unaltered.