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 GetScrollInfo

The GetScrollInfo function retrieves the parameters of a scroll bar, including the minimum and maximum scrolling positions, the page size, and the position of the scroll box (thumb).

Syntax

    BOOL GetScrollInfo(  
        HWND hwnd,
        int fnBar,
        LPSCROLLINFO lpsi
    );

Parameters

• hwnd
  [in] Handle to a scroll bar control or a window with a standard scroll bar, depending on the value of the fnBar parameter.
• fnBar
  [in] Specifies the type of scroll bar for which to retrieve parameters. This parameter can be one of the following values.
  • SB_CTL
    Retrieves the parameters for a scroll bar control. The hwnd parameter must be the handle to the scroll bar control.
  • SB_HORZ
    Retrieves the parameters for the window's standard horizontal scroll bar.
  • SB_VERT
    Retrieves the parameters for the window's standard vertical scroll bar.
• lpsi
  [in, out] Pointer to a SCROLLINFO structure. Before calling GetScrollInfo, set the cbSize member to sizeof(SCROLLINFO), and set the fMask member to specify the scroll bar parameters to retrieve. Before returning, the function copies the specified parameters to the appropriate members of the structure. The fMask member can be one or more of the following values.
  • SIF_PAGE
    Copies the scroll page to the nPage member of the SCROLLINFO structure pointed to by lpsi.
  • SIF_POS
    Copies the scroll position to the nPos member of the SCROLLINFO structure pointed to by lpsi.
  • SIF_RANGE
    Copies the scroll range to the nMin and nMax members of the SCROLLINFO structure pointed to by lpsi.
  • SIF_TRACKPOS
    Copies the current scroll box tracking position to the nTrackPos member of the SCROLLINFO structure pointed to by lpsi.

Return Value

If the function retrieved any values, the return value is nonzero.

If the function does not retrieve any values, the return value is zero. To get extended error information, call GetLastError.

Remarks

The GetScrollInfo function enables applications to use 32-bit scroll positions. Although the messages that indicate scroll-bar position, WM_HSCROLL and WM_VSCROLL, provide only 16 bits of position data, the functions SetScrollInfo and GetScrollInfo provide 32 bits of scroll-bar position data. Thus, an application can call GetScrollInfo while processing either the WM_HSCROLL or WM_VSCROLL messages to obtain 32-bit scroll-bar position data.

To get the 32-bit position of the scroll box (thumb) during a SB_THUMBTRACK request code in a WM_HSCROLL or WM_VSCROLL message, call GetScrollInfo with the SIF_TRACKPOS value in the fMask member of the SCROLLINFO structure. The function returns the tracking position of the scroll box in the nTrackPos member of the SCROLLINFO structure. This allows you to get the position of the scroll box as the user moves it. The following sample code illustrates the technique.

SCROLLINFO si;
case WM_HSCROLL:
    switch(LOWORD(wparam)) {
        case SB_THUMBTRACK:
          // Initialize SCROLLINFO structure
 
            ZeroMemory(&si, sizeof(si));
            si.cbSize = sizeof(si);
            si.fMask = SIF_TRACKPOS;
 
          // Call GetScrollInfo to get current tracking 
          //    position in si.nTrackPos
 
            if (!GetScrollInfo(hwnd, SB_HORZ, &si) )
                return 1; // GetScrollInfo failed
            break;
        .
        .
        .
    }

If the fnBar parameter is SB_CTL and the window specified by the hwnd parameter is not a system scroll bar control, the system sends the SBM_GETSCROLLINFO message to the window to obtain scroll bar information. This allows GetScrollInfo to operate on a custom control that mimics a scroll bar. If the window does not handle the SBM_GETSCROLLINFO message, the GetScrollInfo function fails.

Function Information

• Minimum DLL Version comctl32.dll
• Header Declared in Winuser.h, include Windows.h
• Import library User32.lib
• Minimum operating systems Windows 95, Windows NT 3.51

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Notebook exported on Monday, 7 July 2008, 18:56:50 PM Eastern Daylight Time