Advanced MFC Programming

Chapter 5. Common Controls
……
}
}
if(hwndFocus == hwndEdit)
{
PostMessage(WM_COMBO_RETURN, (WPARAM)IDC_COMBO_DROPDOWN, (LPARAM)0);
return TRUE;
}
First the handle of currently focused window is stored in variable hwndFocus. If it is a valid window
handle, we use m_cbDropDown to get the first child window of IDC_COMBO_DROPDOWN. Then this child
window’s class name is retrieved by calling function ::GetClassName(…). If the class name is “Edit”, we
compare its handle with the focused window handle. Otherwise we need to get the handle of the other child
window before doing the comparison. This will assure that the handle being compared is the handle of the
edit box. If the edit box has the current focus, we post the user defined message WM_COMBO_RETURN, whose
WPARAM parameter is assigned the ID of combo box. Finally a TRUE value is returned to prevent the dialog
box from further processing this message.
Message WM_COMBO_RETURN is processed in class CCCtlDlg. The member function used to trap this
message is CCCtlDlg::OnComboReturn(…). The following code fragment shows how this function is
declared and message mapping is implemented:
Function declaration:
……
……
class CCCtlDlg : public CDialog
{
protected:
};
afx_msg LONG OnComboReturn(UINT, LONG);
DECLARE_MESSAGE_MAP()
Message mapping macros:
……
BEGIN_MESSAGE_MAP(CCCtlDlg, CDialog)
ON_MESSAGE(WM_COMBO_RETURN, OnComboReturn)
END_MESSAGE_MAP()
Function implementation:
LONG CCCtlDlg::OnComboReturn(UINT wParam, LONG lParam)
{
CComboBox *ptrCombo;
CEdit *ptrEdit;
HWND hwndEdit;
CString szStr;
CString szStrLB;
char szClassName[256];
int nSize;
int i;
BOOL bHit;
ptrCombo=(CComboBox *)GetDlgItem(wParam);
ptrEdit=(CEdit *)ptrCombo->GetWindow(GW_CHILD);
hwndEdit=ptrEdit->GetSafeHwnd();
::GetClassName(hwndEdit, szClassName, 256);
if(memcmp(szClassName, "Edit", sizeof("Edit")))
{
ptrEdit=(CEdit *)ptrEdit->GetWindow(GW_HWNDNEXT);
hwndEdit=ptrEdit->GetSafeHwnd();
}
ptrEdit->GetWindowText(szStr);
if(!szStr.IsEmpty())
{
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