CScrollBar的困惑的解决_cscrollbar npos 范围不对-优快云博客

本文链接：https://blog.youkuaiyun.com/arithu/article/details/1826900

本文介绍如何使用GetScrollInfo函数获取滚动条的32位位置数据，尤其是在处理WM_HSCROLL和WM_VSCROLL消息时如何获取滚动条滑块（thumb）的精确位置。

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泡在论坛上看了好多有关CScrollBar的帖子，虽然问题没有直接给出解决方案，但是给了我很多启发，于是我去msdn中大海捞针，知道有这个针，就一定可以找到的。：）
终于被我发现了：
msdn上有讲产生这个问题的原因以及解决方案，感谢csdn和msdn

以下引用自msdn2002：

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(SCROLLINFO));
            si.cbSize = sizeof(SCROLLINFO);
            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;
        .
        .
        .
    }