这是MFC CScrollBar的bug？

[善良超锅锅]

最近使用滚动条时，当把滚动条的范围设置到很大时，滚动条就不能正常使用了，如下图我遇到的情况


滚动条的滑块下拉一段距离后就下拉不了。

我调试的时候发现void CNEWDlg::OnVScroll(UINT nSBCode, UINT nPos, CScrollBar* pScrollBar)的nPos参数有问题。

我本来的滚动条消息处理是这样的（注意case SB_THUMBPOSITION和case SB_THUMBTRACK）

void CNEWDlg::OnVScroll(UINT nSBCode, UINT nPos, CScrollBar* pScrollBar)
 {
	 
	 if (pScrollBar == &m_DiagramSB)
	 {
		 SCROLLINFO si;
		 si.cbSize = sizeof(si);
		 si.fMask = SIF_ALL;
		 pScrollBar->GetScrollInfo(&si, SIF_ALL);
		 int pos = si.nPos;

		 switch (nSBCode)
		 {
		 case SB_TOP:
			 pos = 1;
			 break;

		 case SB_BOTTOM:
			 pos = si.nMax;
			 break;

		 case SB_ENDSCROLL:
			 break;

		 case SB_LINEDOWN:
			 pos++;
			 break;

		 case SB_LINEUP:
			 pos--;
			 break;

		 case SB_PAGEDOWN:
		 {
			 
			 if (pos < si.nMax)
				 pos = min(si.nMax, pos + (int)si.nPage);
		 }
			 break;

		 case SB_PAGEUP:
		 {
			 if (pos > si.nMin)
				 pos = max(si.nMin, pos - (int)si.nPage);
		 }
			 break;

		 case SB_THUMBPOSITION:
			 pos = nPos,;
			 break;

		 case SB_THUMBTRACK:
			 pos =nPos,;
			 break;

		 default:
			 break;
		 }

		 //ZeroMemory(&si, sizeof(si));
		 si.cbSize = sizeof(si);
		 si.fMask = SIF_POS;
		 si.nPos = pos;
		 pScrollBar->SetScrollInfo(&si);
	 }
	 
	 CDialogEx::OnVScroll(nSBCode, nPos, pScrollBar);

	 // 刷新示意图子窗口
	 RECT rc;
	 GetDlgItem(IDC_DIAGRAM)->GetWindowRect(&rc);
	 ScreenToClient(&rc);
	 InvalidateRect(&rc, FALSE);
	 UpdateWindow();
 }

我调试的时候发现滚动条的滑块下拉一段距离后nPos就变成一个很大很大的数，赋值给pos后发生了翻转，使pos成了负数。滑块无法下拉的原因正在与此。我把上面的nPos用si.nTrackPos就好了。

问题解决了，但是我很疑惑：OnVScroll方法是MFC框架提供的，为什么参数会有问题呢？

[schlafenhamster]

SIF_POS The nPos member contains the scroll box position, which is not updated while the user drags the scroll box. SIF_TRACKPOS The nTrackPos member contains the current position of the scroll box while the user is dragging it. 参考 void CxxxxDlg::OnVScroll(UINT nSBCode, UINT nPos, CScrollBar* pScrollBar) { // TODO: Add your message handler code here and/or call default SCROLLINFO ScrollInfo; ScrollInfo.cbSize=sizeof(ScrollInfo); ScrollInfo.fMask = SIF_ALL; GetScrollInfo(SB_VERT,&ScrollInfo); // int delta=0; switch(nSBCode) { case SB_TOP: case SB_LINEUP: if(ScrollInfo.nPos > ScrollInfo.nMin) delta = -SCROLL_STEP; break; case SB_BOTTOM: case SB_LINEDOWN: if(ScrollInfo.nPos < (ScrollInfo.nMax-(int)ScrollInfo.nPage)) delta = SCROLL_STEP; break; case SB_THUMBTRACK: case SB_THUMBPOSITION: delta = ScrollInfo.nTrackPos-ScrollInfo.nPos; break; } if(delta !=0 ) {// you can adjust m_Offset in OnInitDialog() for "abc" start point m_vbPos -= delta; ScrollWindow(0,-delta); UpdateWindow(); ScrollInfo.nPos += delta; ScrollInfo.fMask=SIF_POS | SIF_RANGE; SetScrollInfo(SB_VERT,&ScrollInfo); } // CDialog::OnVScroll(nSBCode, nPos, pScrollBar); }

[hurryboylqs]

你可以参考这个 http://www.codeproject.com/Articles/10902/Add-Scrolling-to-a-CWnd-or-CDialog-using-a-C-Helpe