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 WM_HSCROLL

The WM_HSCROLL message is sent to a window when a scroll event occurs in the window's standard horizontal scroll bar. This message is also sent to the owner of a horizontal scroll bar control when a scroll event occurs in the control.

A window receives this message through its WindowProc function.

Syntax

    LRESULT CALLBACK WindowProc(
      HWND hwnd,       // handle to window
      UINT uMsg,       // WM_HSCROLL
      WPARAM wParam,   // request and position
      LPARAM lParam    // handle to scroll bar (HWND)
    );

Parameters

• wParam
  The low-order word specifies a scroll bar value that indicates the user's scrolling request. This word can be one of the following values. Value Meaning
  • SB_ENDSCROLL
    Ends scroll.
  • SB_LEFT
    Scrolls to the upper left.
  • SB_RIGHT
    Scrolls to the lower right.
  • SB_LINELEFT
    Scrolls left by one unit.
  • SB_LINERIGHT
    Scrolls right by one unit.
  • SB_PAGELEFT
    Scrolls left by the width of the window.
  • SB_PAGERIGHT
    Scrolls right by the width of the window.
  • SB_THUMBPOSITION
    The user has dragged the scroll box (thumb) and released the mouse button. The high-order word indicates the position of the scroll box at the end of the drag operation.
  • SB_THUMBTRACK
    The user is dragging the scroll box. This message is sent repeatedly until the user releases the mouse button. The high-order word indicates the position that the scroll box has been dragged to.
    The high-order word specifies the current position of the scroll box if the low-order word is SB_THUMBPOSITION or SB_THUMBTRACK; otherwise, this word is not used.
• lParam
  If the message is sent by a scroll bar, then this parameter is the handle to the scroll bar control. If the message is not sent by a scroll bar, this parameter is NULL.

Return Values

If an application processes this message, it should return zero.

Remarks

The SB_THUMBTRACK request code is typically used by applications that provide feedback as the user drags the scroll box.

If an application scrolls the content of the window, it must also reset the position of the scroll box by using the SetScrollPos function.

Note that the WM_HSCROLL message carries only 16 bits of scroll box position data. Thus, applications that rely solely on WM_HSCROLL (and WM_VSCROLL) for scroll position data have a practical maximum position value of 65,535.

However, because the SetScrollInfo, SetScrollPos, SetScrollRange, GetScrollInfo, GetScrollPos, and GetScrollRange functions support 32-bit scroll bar position data, there is a way to circumvent the 16-bit barrier of the WM_HSCROLL and WM_VSCROLL messages. See GetScrollInfo for a description of the technique.

Requirements

• Windows NT/2000 or later: Requires Windows NT 3.1 or later.
• Windows 95/98/Me: Requires Windows 95 or later.
• Header: Declared in Winuser.h; include Windows.h.

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