ScrollBar Control
The scrollbar control provides a visual approach to setting a value. It consists of a vertical/horizontal bar and enclosed scroll box. The user can use a mouse click or drag action to reposition the scroll box, which in turn changes the position property of the scroll bar. The position of a scrollbar takes on a value bounded by the scrollbar's range (hi and lo values).

Scrollbars are often located on the right/bottom sides of dialogs, but may be aligned with any edge of its parent dialog.

A scrollbar can also be added to a dialog using the dialog style& properties. In that case, there is no child control to monitor and all events go directly to the dialog callback function.

Arguments
The Control Add statement is used to create all new controls. Here are the statement's arguments and any special significance to the scrollbar control.

Usage Notes
A scrollbar has three parts - body, scroll box, and arrows. The location of the scroll box visually indicates the position (value) of the scrollbar. The position is constrained to a range of values (lo and hi).

Lo is the bottom position in a vertical scrollbar and left-most position in a horizontal scrollbar.

Hi is the top position in a vertical scrollbar and right-most position in a horizontal scrollbar.

Clicking on arrows is associated with a making a small value change. If the click is on the hi side of the scroll box, the value increases. If the click is on the lo side of the scroll box, the value decreases.

Clicking on the body is associated with a making a larger value change. If the click is on the hi side of the scroll box, the value increases. If the click is on the lo side of the scroll box, the value decreases.

The user can also change the value of the scrollbar by dragging the scroll box to a new position.

Regardless of how the new value is assigned, the position of the scroll box must be made programmatically.

To align the scrollbar with an edge, use one of the %sbs_xxx alignment styles with the corresponding %sbs_xxx vert/horz style. Also set x,y to 0,0 and set xx,yy to the size of the client area. In this approach, remember that the scrollbar will not automatically change size when the Dialog size is changed. The application must handle resizing of the scrollbar control.

With %sbs_vert, a scrollbar is always displayed vertically. But with %sbs_horz, if width is less than height the scrollbar is automatically switched to %sbs_vert.

To get bottom or top alignment, the %sbs_horz must be used in combination with %sbs_bottomalign or %sbs_topalign.

To get left or right alignment, the %sbs_vert must be used in combination with %sbs_leftalign or %sbs_rightalign.

ScrollBar-Specific PowerBASIC Statements
PowerBASIC provides several statements specific to the scrollbar control. These allow getting/setting scrollbar properties.

See the Usage section above for information on how to use the values made available by these statements.

Messages, Notifications, Styles, and ExtSstyles
There are four types of named constants in the following table. All are pulled from the MSDN web site.

The first column contains control-specific named constants and the second column contains generic window named constants (scrollbar controls are windows).

Also, if the PowerBASIC Help file has an entry on the value, it is highlighted in yellow. If the value was noted in PowerBASIC Help as a default value, it is also shown in bold text.

In the values for notifications, descriptions starting with -n and -c refer to events received through the %wm_notify and %wm_command messages. By default, PowerBASIC controls can receive both of these messages.

   

And here is a short description of many of the named constants corresponding to notifications, styles, and extstyle - particularly those discussed in the PowerBASIC Help topics.

%sb_bottom - scrolls to lower right %sb_endscroll - ends scroll %sb_endscroll - ends scroll %sb_left - scroll to upper left %sb_linedown - scrolls one line down %sb_lineleft - scrolls left by one unit %sb_lineright - scrolls right by one unit %sb_lineup - scrolls one line up %sb_pagedown - scrolls one page down %sb_pageleft - scrolls left by the width of the window %sb_pageright - scrolls right by the width of the window %sb_pageup - scrolls one page up %sb_right - scroll to lower right %sb_thumbposition - scroll box dragged and released %sb_thumbposition - scroll box dragged and released %sb_thumbtrack - scroll box is being dragged %sb_thumbtrack - scroll box is being dragged %sb_top - scrolls to upper left %sbs_bottomalign - align scrollbar bottom with dialog bottom %sbs_horz - horizontal scroll bar %sbs_leftalign - align left edge with dialog left edge %sbs_rightalign - align right edge with dialog right edge %sbs_topalign - align top edge with dialog top edge %sbs_vert - vertical scroll bar %wm_ctlcolorscrollbar - control about to be drawn %wm_hscroll - horizontal scroll event %wm_vscroll - vertical scroll event %ws_disabled - initially disabled (no user input) %ws_ex_clientedge - apply sunken edge border %ws_ex_left - generic left-aligned properties %ws_ex_right - generic right-aligned properties %ws_ex_staticedge - apply 3D border %ws_ex_windowedge - apply raised edge border %ws_group - starts/ends group. use %ws_tabstop style. %ws_tabstop - allows receipt of keyboard focus

Callback Function
A control can have its own callback function, or use the parent dialog callback function.

A control callback function should return TRUE to indicate it has processed the message. This prevents unnecessarily calling the dialog callback function, which will process the message if no control callback function is available, or if the control callback function returns FALSE.

By default, both %WM_COMMAND and %WM_NOTIFY messages are received. However, if the #MESSAGE COMMAND compiler directive is invoked, the %WM_NOTIFY messages will not be available.

The scrollbar also receives the %WM_SCROLL and %WM_VSCROLL messages. In both cases, the low word of wParam contains the event information.

Here's a sample scrollbar control callback function. 

   CallBack Function cbScrollBar()
      Select Case CB.MSG
         Case %WM_HSCROLL
            Select Case LO(WORD, CB.WPARAM)
               Case %sb_endscroll      'mouse up (arrow/shaft)
               Case %sb_left           'HOME keypress
               Case %sb_right          'END keypress
               Case %sb_lineleft       'arrow
               Case %sb_lineright      'arrow
               Case %sb_pageleft       'shaft
               Case %sb_pageright      'shaft
               Case %sb_thumbposition  'scroll box
               Case %sb_thumbtrack     'scroll box
            End Selection
         Case %WM_VSCROLL
            Select Case LO(WORD, CB.WPARAM)
               Case %sb_bottom          'END keypress
               Case %sb_endscroll       'mouse up (arrow/shaft)
               Case %sb_linedown        'arrow
               Case %sb_lineup          'arrow
               Case %sb_pagedown        'shaft
               Case %sb_pageup          'shaft
               Case %sb_thumbposition   'scrollbox
               Case %sb_thumbtrack      'scrollbox
               Case %sb_top             'HOME keypress
            End Selection
      End Select
   End Function

To help clarify which parts of a scrollbar correspond to received messages, here is a diagram of the parts of a scrollbar.

CONTROL Statement Syntax
The following table lists the various Control statements (except the ADD statements). Most, but not all, can be used with the scrollbar control. A one-line description of the statement and then its syntax are presented.

If you have any suggestions or corrections, please let me know.