Drawitem is not getting calling

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MFC

VC++

i have created my own custom control class CMyComboBox and its derived from CCombobox.
i have added DrawItem as virtual function but this function is not getting called when loading my dailog
could you please tell me how to call drawitem here
2) i need toget the all the combobox functionalities in this class
could you please give me some suggestions on this

What I have tried:

oid CMyComboBox::DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct)
{
ASSERT(lpDrawItemStruct->CtlType == ODT_COMBOBOX);
LPCTSTR lpszText = (LPCTSTR) lpDrawItemStruct->itemData;
ASSERT(lpszText != NULL);
CDC dc;

dc.Attach(lpDrawItemStruct->hDC);

// Save these value to restore them when done drawing.
COLORREF crOldTextColor = dc.GetTextColor();
COLORREF crOldBkColor = dc.GetBkColor();

// If this item is selected, set the background color
// and the text color to appropriate values. Erase
// the rect by filling it with the background color.
if ((lpDrawItemStruct->itemAction & ODA_SELECT) &&
(lpDrawItemStruct->itemState & ODS_SELECTED))
{
dc.SetTextColor(::GetSysColor(COLOR_HIGHLIGHTTEXT));
dc.SetBkColor(::GetSysColor(COLOR_HIGHLIGHT));
dc.FillSolidRect(&lpDrawItemStruct->rcItem, ::GetSysColor(COLOR_HIGHLIGHT));
}
else
{
dc.FillSolidRect(&lpDrawItemStruct->rcItem, crOldBkColor);
}

// Draw the text.
dc.DrawText(
lpszText,
(int)_tcslen(lpszText),
&lpDrawItemStruct->rcItem,
DT_CENTER|DT_SINGLELINE|DT_VCENTER);

// Reset the background color and the text color back to their
// original values.
dc.SetTextColor(crOldTextColor);
dc.SetBkColor(crOldBkColor);

dc.Detach();
}