Create derived control at runtime cause assertion - mfc

Question

I am trying to create a control at run-time, but it causes assertion, and I don't know what's causing it. The control I am using is the Tree ComboBox Control from this link: https://www.codeproject.com/Articles/187762/Tree-ComboBox-Control
I added the code to register the class as follow:
CTreeComboBox::CTreeComboBox()
...
{
...
RegisterWindowClass();
}
CTreeComboBox::~CTreeComboBox()
{
m_BrushAlert.DeleteObject();
}
BOOL CTreeComboBox::RegisterWindowClass()
{
WNDCLASS wndcls;
HINSTANCE hInst = AfxGetInstanceHandle();
if (!(::GetClassInfo(hInst, _T("TreeComboBox"), &wndcls)))
{
wndcls.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;
wndcls.lpfnWndProc = ::DefWindowProc;
wndcls.cbClsExtra = wndcls.cbWndExtra = 0;
wndcls.hInstance = hInst;
wndcls.hIcon = NULL;
wndcls.hCursor = AfxGetApp()->LoadStandardCursor(IDC_ARROW);
wndcls.hbrBackground = (HBRUSH)(COLOR_3DFACE + 1);
wndcls.lpszMenuName = NULL;
wndcls.lpszClassName = _T("TreeComboBox");
if (!AfxRegisterClass(&wndcls))
{
AfxThrowResourceException();
return FALSE;
}
}
return TRUE;
}
I tried to create the control at run-time using the following code in the test program:
BOOL CTestComboBoxDlg::OnInitDialog()
{
...
m_ComboBox2.CreateEx(WS_EX_CLIENTEDGE, _T("TreeComboBox"), _T(""), WS_CHILD | WS_VISIBLE | CBS_DROPDOWNLIST | WS_VSCROLL | WS_TABSTOP,
CRect(0, 0, 100, 50), this, 100000, NULL);
return TRUE; // return TRUE unless you set the focus to a control
}
I also tried creating the control using a button click event thinking that I should let the GUI finish initializing, but the same error occur:
void CTestComboBoxDlg::OnBnClickedButton1()
{
m_ComboBox2.CreateEx(WS_EX_CLIENTEDGE, _T("TreeComboBox"), _T(""), WS_CHILD | WS_VISIBLE | CBS_DROPDOWNLIST | WS_VSCROLL | WS_TABSTOP,
CRect(0, 0, 100, 50), this, 100000, NULL);
}
When I run the program, it stopped at the file dbgrptt.cpp at the following line:
__try
{
if (_CRT_ASSERT == nRptType && _InterlockedIncrement(&_crtAssertBusy) > 0)
{
/* use only 'safe' functions -- must not assert in here! */
_ERRCHECK(_itoa_s(nLine, szLineMessage, DBGRPT_MAX_MSG, 10));
OutputDebugStringA("Second Chance Assertion Failed: File ");
OutputDebugStringA(szFile ? szFile : "<file unknown>");
OutputDebugStringA(", Line ");
OutputDebugStringA(szLineMessage);
OutputDebugStringA("\n");
It stop here===> _CrtDbgBreak();
retval=-1;
__leave;
}
The program run fine if I create the control manually using the Visual Studio GUI editor, so I am not sure what's wrong. Can you help me figure out how to create this control at run-time?
Note: change the statement: TRACE1(_T("Item selected: %s\n"), GetItemText(hItem)); to TRACE(_T("Item selected: %s\n"), GetItemText(hItem)); in the file ComboTreeCtrlExt.cpp if you if you want to run the code and are using MFC

Answer 1

To answer my own question. Move the following code from the CTreeComboBox::PreSubclassWindow() to the CTreeComboBox::OnCreate()
CRect rect(0, 0, 0, 0);
DWORD dwStyle = WS_POPUP | WS_BORDER;
CWnd* pWnd = &m_Tree;
pWnd->CreateEx(0, WC_TREEVIEW, NULL, dwStyle, rect, GetParent(), 0, NULL);
m_Tree.Init(this);
GetClientRect(rect);
SetDroppedWidth(rect.Width());
SetDroppedHeight(m_nDroppedHeight);
dwStyle = CBS_DROPDOWNLIST & GetStyle();
ASSERT(CBS_DROPDOWNLIST == dwStyle);