演示垂直滚动条CScrollbar控件的使用

/*
Title:演示垂直滚动条CScrollbar控件的使用
Description: OnVScroll demo
Environment: VS2010SP1
Author:kagula
Date:2015-8-11
*/

//set scrollbar knob position
void CtestScrollDlg::OnVScroll(UINT nSBCode, UINT nPos, CScrollBar* pScrollBar)
{
int nMax;
int nMin;
pScrollBar->GetScrollRange(&nMin,&nMax);

int currentPos = pScrollBar->GetScrollPos();
int stride = (nMax-nMin)/10;

#ifdef _DEBUG
TRACE(L"pScrollBar->GetScrollPos()=%d\n",currentPos);
#endif

switch(nSBCode)
{
case SB_THUMBPOSITION://Drop knob
case SB_THUMBTRACK://Drag knob
pScrollBar->SetScrollPos(nPos);
break;
case SB_LINEUP: //click up arrow
case SB_PAGEUP: //stroke page up in keyboard
if((currentPos-stride)>nMin)
currentPos-=stride;
else
currentPos=nMin;
pScrollBar->SetScrollPos(currentPos);
break;
case SB_LINEDOWN: //click down arrow
case SB_PAGEDOWN: //stroke page down in keyboard
if((currentPos+stride)<nMax)
currentPos+=stride;
else
currentPos=nMax;
pScrollBar->SetScrollPos(currentPos);
break;
}

CDialogEx::OnVScroll(nSBCode, nPos, pScrollBar);
}

//create scrollbar controller
void CtestScrollDlg::OnBnClickedBtnAdd()
{
if (m_pScrollbar==nullptr)
{
CRect rect;
GetClientRect(rect);
rect.left = rect.right - GetSystemMetrics(SM_CXVSCROLL);

m_pScrollbar = new CScrollBar;
m_pScrollbar->Create(WS_VISIBLE|SB_VERT,rect,this,IDC_SCROLLBAR1);
m_pScrollbar->SetScrollRange(0,100);
}
}

//release scrollbar controller
void CtestScrollDlg::OnBnClickedBtnDel()
{
if (m_pScrollbar)
{
m_pScrollbar->DestroyWindow();
delete m_pScrollbar;
m_pScrollbar = nullptr;
}
}

void CtestScrollDlg::OnDestroy()
{
CDialogEx::OnDestroy();

OnBnClickedBtnDel();
}