CScrollbar SetScrollInfo has no effect - c++

Question

I have similar problem to this one: How do you use MFC CScrollbar controls? but I figured out that my ON_WM_VSCROLL message is sending parameter nPos always equal 0. I thought that I should set the scrollbar with SetScrollInfo method or at least with SetScrollRange, and I try to do it in the PreCreateWindow() of a View class function (which is derived from CFormView).
Nevertheless the scrollbar doesn't seem to get data from the SCROLLINFO structure.
Here are my code samples:
BOOL CInterfaceView::PreCreateWindow(CREATESTRUCT& cs)
{
// TODO: Modify the Window class or styles here by modifying
// the CREATESTRUCT cs
drawphoto=false; //other unrelated variables;
zoomfactor=1.0;
info1.cbSize=sizeof(SCROLLINFO); //SCROLLINFO global variable
info1.fMask=SIF_ALL;
info1.nMin=0;
info1.nMax=100;
info1.nPage=2;
info1.nPos=5;
info1.nTrackPos=2;
ScrollBar1.SetScrollInfo(&info1); //the vertical ScrollBar
// ScrollBar1.SetScrollRange(0,100); //this has no effect either
return CFormView::PreCreateWindow(cs);
}
VSCROLL message handler:
void CInterfaceView::OnVScroll(UINT nSBCode, UINT nPos, CScrollBar* pScrollBar)
{
int CurPos = pScrollBar->GetScrollPos();
//debug code:
CString test;
int rn,rx;
pScrollBar->GetScrollRange(&rn,&rx);
test.Format(_T("%d %d %d\n"),nPos,CurPos,rx-rn);
if(pScrollBar!=NULL)
TRACE(test+_T(" dzialamy\n"));
//end debug code
//this part found on the Internet
// Determine the new position of scroll box.
switch (nSBCode)
{
case SB_LEFT: // Scroll to far left.
CurPos = 0;
break;
case SB_RIGHT: // Scroll to far right.
CurPos = 100;
break;
case SB_ENDSCROLL: // End scroll.
break;
case SB_LINELEFT: // Scroll left.
if (CurPos > 0)
CurPos--;
break;
case SB_LINERIGHT: // Scroll right.
if (CurPos < 100)
CurPos++;
break;
case SB_PAGELEFT: // Scroll one page left.
{
// Get the page size.
SCROLLINFO info;
ScrollBar1.GetScrollInfo(&info, SIF_ALL);
if (CurPos > 0)
CurPos = max(0, CurPos - (int) info.nPage);
}
break;
case SB_PAGERIGHT: // Scroll one page right
{
// Get the page size.
SCROLLINFO info;
ScrollBar1.GetScrollInfo(&info, SIF_ALL);
if (CurPos < 100)
CurPos = min(100, CurPos + (int) info.nPage);
}
break;
case SB_THUMBPOSITION: // Scroll to absolute position. nPos is the position
CurPos = nPos; // of the scroll box at the end of the drag operation.
break;
case SB_THUMBTRACK: // Drag scroll box to specified position. nPos is the
CurPos = nPos; // position that the scroll box has been dragged to.
break;
}
// Set the new position of the thumb (scroll box).
ScrollBar1.SetScrollPos(50); //orignally it was CurPos
CFormView::OnVScroll(nSBCode, 50, pScrollBar);
// ScrollBar1.SetScrollPos(nPos);
}
So I suspect, that I try to set the scrollbar either in wrong place, or do something wrong with it? I appreciate any help.

Answer 1

PreCreateWindow is called before the window (and its scroll bar) have been created. In a view class you should do the initialization in OnInitialUpdate. This is called after window creation but before the window becomes visible.

Answer 2

I think that PreCreateWindow() is too early to set up your scrollbar, the "proper" place would be when your CDocument-derived class has loaded/modified data which would affect the range of the scroll bar.