仅为初学者提供。

1、在xml文件中，有如下关系：

<Shops>
<Shop NO="0" Name="山东省">
<Units>
<Unit NO="0">济南</Unit>
<Unit NO="1">青岛</Unit>
<Unit NO="2">潍坊</Unit>
<Unit NO="3">烟台</Unit>
</Units>
</Shop>
<Shop NO="1" Name="湖南省">
<Units>
<Unit NO="0">长沙</Unit>
<Unit NO="1">张家界</Unit>
<Unit NO="2">益阳</Unit>
</Units>
</Shop>
</Shops>

	
	xml.FindElem(_T("Shops"));
	xml.IntoElem();	
	while(xml.FindElem())
	{
		((CComboBox*)GetDlgItem(IDC_SHOP))->AddString(xml.GetAttrib(_T("Name")));
	}
	((CComboBox*)GetDlgItem(IDC_SHOP))->SetCurSel(0);
	xml.OutOfElem();

	xml.FindElem(_T("Shops"));
	xml.IntoElem();
	xml.ResetMainPos();
        xml.FindElem();
	xml.IntoElem();
	xml.FindElem(_T("Units"));
	xml.IntoElem();	
	while(xml.FindElem())
	{
		((CComboBox*)GetDlgItem(IDC_UNIT))->AddString(xml.GetData());
	}
	((CComboBox*)GetDlgItem(IDC_UNIT))->SetCurSel(0);
	xml.OutOfElem();
	xml.OutOfElem();
	xml.OutOfElem();

void CDlgUnit::OnSelchangeShop() 
{
	// TODO: Add your control notification handler code here
	((CComboBox*)GetDlgItem(IDC_UNIT))->ResetContent();

	CString strShop;
	int i=((CComboBox*)GetDlgItem(IDC_SHOP))->GetCurSel();
	((CComboBox*)GetDlgItem(IDC_SHOP))->GetLBText(i,strShop);
	
	CMarkup xml;//CMarkup是有关xml文件的解读，网上有文件，可以直接使用。
	xml.Load(GetCurDir()+_T("123.INI"));//123.INI是xml文件的名称。
	xml.ResetPos();
	xml.FindChildElem();
	xml.IntoElem();	

	xml.FindElem(_T("Shops"));
	xml.IntoElem();
	
	while(xml.FindElem()){
		if(xml.GetAttrib(_T("Name"))==strShop)
		{
			xml.IntoElem();
			xml.FindElem(_T("Units"));
			xml.IntoElem();	
			while(xml.FindElem()){
				((CComboBox*)GetDlgItem(IDC_UNIT))->AddString(xml.GetData());
			}
			((CComboBox*)GetDlgItem(IDC_UNIT))->SetCurSel(0);
			break;
		}		
	}	
}