C / C++ / MFC

pCombo->DeleteString(2);
pCombo->DeleteString(3);
pCombo->ShowDropDown(TRUE);

They sought it with thimbles, they sought it with care;
They pursued it with forks and hope;
They threatened its life with a railway-share;
They charmed it with smiles and soap.

//#include <windows.h>
//#pragma comment(lib, "user32.lib")

void CYourDialog::Test()
{
  CComboBox* pcBox = (CComboBox*) GetDlgItem(IDC_COMBO1);
  if (pcBox->GetSafeHwnd()) {
    pcBox->ShowDropDown(TRUE);
    
    COMBOBOXINFO sCBINFO = {0};
    sCBINFO.cbSize = sizeof(COMBOBOXINFO);
    
    if (::GetComboBoxInfo(pcBox->GetSafeHwnd(), &sCBINFO)) {
      if (sCBINFO.hwndList) {
        CWnd* pcList = CWnd::GetFromHandle(sCBINFO.hwndList);
        CRect cListRect;
        pcList->GetWindowRect(cListRect);
        cListRect.bottom -= 20;
        pcList->MoveWindow(cListRect);
      }
    }
  }
}

They sought it with thimbles, they sought it with care;
They pursued it with forks and hope;
They threatened its life with a railway-share;
They charmed it with smiles and soap.

void CYourDialog::AdjustComboBox(CComboBox* pcBox)
{
  if (pcBox->GetSafeHwnd()) {    
    COMBOBOXINFO sCBINFO = {0};
    sCBINFO.cbSize = sizeof(COMBOBOXINFO);
    if (::GetComboBoxInfo(pcBox->GetSafeHwnd(), &sCBINFO)) {
      if (sCBINFO.hwndList) {
        CWnd* pcList = CWnd::FromHandle(sCBINFO.hwndList);
        CRect cListRect;
        pcList->GetWindowRect(cListRect);
        // do not worry, the bottom will be correctly adjusted:
        cListRect.bottom = cListRect.top; 
        pcList->MoveWindow(cListRect);
      }
    }
  }
}

They sought it with thimbles, they sought it with care;
They pursued it with forks and hope;
They threatened its life with a railway-share;
They charmed it with smiles and soap.

mesajflaviu wrote:

I use VC6 , so I have not access to GetComboBoxInfo method...

// Resize combobox according to actual element count
int m_MaxHeightItems = 10;
int visibleItemCount =  m_MaxHeightItems < nNumEntries ? m_MaxHeightItems : nNumEntries;
CRect rectExpanded;
pCombo->GetClientRect(rectExpanded);
rectExpanded.bottom += visibleItemCount * pCombo->GetItemHeight(0);
rectExpanded.bottom += GetSystemMetrics(SM_CYEDGE) * 2; // top & bottom edges
pCombo->SetWindowPos(NULL,              // not relative to any other windows
                        0, 0,           // TopLeft corner doesn't change
                        rectExpanded.Width(), rectExpanded.Height(),   // existing width, new height
                        SWP_NOMOVE | SWP_NOZORDER       // don't move box or change z-ordering.
                        );