Keyboard Interface for a Scroll Bar - Win32 Programmer's Reference

Keyboard Interface for a Scroll Bar

A scroll bar control provides a built-in keyboard interface that enables the user to issue scrolling requests by using the keyboard; a standard scroll bar does not. When a scroll bar control has the keyboard focus, it sends WM_HSCROLL and WM_VSCROLL messages to its parent window when the user presses the arrow keys. The notification message is sent with each message corresponding to the arrow key the user has pressed. Following are the arrow keys and their corresponding notification messages.

Arrow key	Notification message
DOWN	SB_LINEDOWN or SB_LINERIGHT
END	SB_BOTTOM
HOME	SB_TOP
LEFT	SB_LINEUP or SB_LINELEFT
PGDN	SB_PAGEDOWN or SB_PAGERIGHT
PGUP	SB_PAGEUP or SB_PAGELEFT
RIGHT	SB_LINEDOWN or SB_LINERIGHT
UP	SB_LINEUP or SB_LINELEFT

Note that the keyboard interface of a scroll bar control sends the SB_TOP and SB_BOTTOM notification messages. The SB_TOP message indicates that the user has reached the top value of the scrolling range. An application scrolls the window content downward so that the top of the data object is visible. The SB_BOTTOM message indicates that the user has reached the bottom value of the scrolling range. If an application processes the SB_BOTTOM message, it scrolls the window content upward so that the bottom of the data object is visible.

If you want a keyboard interface for a standard scroll bar, you can create one yourself by processing the WM_KEYDOWN message in your window procedure and then performing the appropriate scrolling action based on the virtual-key code that accompanies the message. For information about how to create a keyboard interface for a scroll bar, see Creating a Keyboard Interface for a Standard Scroll Bar.

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