Standard Scroll Bars and Scroll Bar Controls

A scroll bar is included in a window either as a standard scroll bar or as a scroll bar control. A standard scroll bar is located in the nonclient area of a window. It is created with the window and displayed when the window is displayed. The sole purpose of a standard scroll bar is to enable the user to generate scrolling requests for viewing the entire content of the client area. You can include a standard scroll bar in a window by specifying WS_HSCROLL, WS_VSCROLL, or both styles when you create the window. The WS_HSCROLL style creates a horizontal scroll bar positioned at the bottom of the client area. The WS_VSCROLL style creates a vertical scroll bar positioned at the right of the client area. The SM_CXHSCROLL and SM_CYHSCROLL system metric values define the width and height of a standard horizontal scroll bar. The SM_CXVSCROLL and SM_CYVSCROLL values define the width and height of a standard vertical scroll bar.

A scroll bar control is a control window that belongs to the SCROLLBAR window class. A scroll bar control appears and functions like a standard scroll bar, but it is a separate window. As a separate window, a scroll bar control receives direct input focus, indicated by a flashing caret displayed in the scroll box. Unlike a standard scroll bar, a scroll bar control also has a built-in keyboard interface that enables the user to direct scrolling. You can use as many scroll bar controls as needed in a single window. When you create a scroll bar control, you must specify the scroll bar's size and position. However, if a scroll bar control's window can be resized, adjustments to the scroll bar's size must be made whenever the size of the window changes.

The advantage of using a standard scroll bar is that Windows creates the scroll bar and automatically sets its size and position. However, standard scroll bars are sometimes too restrictive. For example, suppose that you want to divide a client area into quadrants and use a separate set of scroll bars to control the content of each quadrant. You cannot use standard scroll bars because you can only create one set of scroll bars for a particular window. Use scroll bar controls instead, because you can add as many of them to a window as you want.

Applications can provide scroll bar controls for purposes other than scrolling the content of a window. For example, a screen saver application might provide a scroll bar for setting the speed at which graphics are moved about on the screen.

A scroll bar control can have a number of styles that serves to control the orientation and position of the scroll bar. You specify the styles that you want when you call the CreateWindowEx function to create a scroll bar control. Some of the styles create a scroll bar control that uses a default width or height. However, you must always specify the x- and y-coordinates and the other dimensions of the scroll bar. Following are the scroll bar control styles.