C / C++ / MFC

if(m_dialogHwnd == NULL)
{
    ShowWindow(m_dialogHwnd, SW_SHOW);
}

if(m_dialogHwnd != NULL)
{
    ShowWindow(m_dialogHwnd, SW_SHOW);
}

#pragma once

#include "WPFInDialogDefs.h"
#include "WPFWrapper.h"

// This class is exported from the WPFInDialog.dll
class WPFINDIALOG_API CWPFInDialog {
public:
	CWPFInDialog(void);
	void CreateMyDialog(HWND a_hwnd);
private:
	HWND m_dialogHwnd;
	CWPFWrapper m_wrapper;
};

#include "stdafx.h"
#include "WPFInDialog.h"
#include "resource.h"

extern HINSTANCE  g_hinstDLL;

CWPFInDialog::CWPFInDialog()
{
}

BOOL CALLBACK ToolDlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam)
{
	switch(Message)
	{
		case WM_COMMAND:
			break;
		default:
			return FALSE;
	}
	return TRUE;
}

void CWPFInDialog::CreateMyDialog(HWND a_hwnd)
{
	m_dialogHwnd = CreateDialog(g_hinstDLL, MAKEINTRESOURCE(IDD_DIALOGHOST), a_hwnd, ToolDlgProc);
	if(m_dialogHwnd != NULL)
	{
		ShowWindow(m_dialogHwnd, SW_SHOW);
	}
}

CWPFInDialog* l_atsWrapper = new CWPFInDialog();
l_atsWrapper->CreateMyDialog(l_hwndExcel);

CComPtr<Excel::_Application> l_excelApp;
HRESULT l_hr = g_excelMgrSingleton.GetExcelApplication(&l_excelApp);

HWND l_hwndExcel;
l_hr = l_excelApp->get_Hwnd((long*)&l_hwndExcel);

Richard MacCutchan wrote:

However, I did notice that your return value for the WM_GETDLGCODE[^] message is not one of the valid options.