Scroll Bars

Scroll Bars

---

A scrollbar is a vertical or horizontal bar on a window with a little box inside it (called the slider or " thumb") that can be dragged along it with the mouse. Applications use the scrollbar not only to set the position of something (such as the text cursor in a textbox or the currently displayed page of a word processor document), but to give us visual feedback of where we are and how much stuff we can't see. The thumb shows us where we are in the entire piece of text, and the size of the thumb shows us what percentage we're viewing. (A large thumb means that most of what's there is visible and a small thumb means that there's a lot we can't see.) The scrollbar usually becomes disabled (grayed out) if there's no scrolling to be done.

Click the up or down arrows to move the scroll bar incrementally, or drag the thumb with the mouse to move to the desired position. You can also click in the gray areas between the arrows and the thumb to move up or down a page at a time.

It is possible to use the cursor keys and PgUp/PgDn keys to control the scrollbar if it has the focus. If the scrollbar is part of another control, such as the textbox shown in Figure 3-22, then it cannot receive the focus to receive keyboard input directly. Instead, use the cursor keys to navigate in the listbox or input field with which the scrollbar is associated. The thumb blinks if it has the focus.

Figure 3-24. Use scrollbars to view all of the items in a folder when the folder window is not sufficiently large