Load a child dialog from a dynamic DLL

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Introduction

This article explains how to use a child window (dialog) exported from a dynamically loaded DLL.

Background

Using the Visual Studio 6.0 environment, I created an MFC (SDI) application and selected the DLL and exported the symbols options.

Using the code

The DLL implementation

Here's the declaration:

/*
*
*       Lee Gun-woo,
*       http://AiRPAGE.ORG
*       Load a child dialog from DLL !!
*
*/
// TestDlgDll.h
//
#ifndef __MYDLG_H__
#define __MYDLG_H__


#ifdef MYDLG_API_EXPORTS
#define MYDLG_API __declspec(dllexport)
#else
#define MYDLG_API __declspec(dllimport)
#endif

class CTestDlgDll
{
public:
 void CreateMyDialog(HWND hWnd);
 void CloseMyDialog();
protected:
 /** @brief constructor */
 CTestDlgDll();
 /** @brief destructor */
 virtual ~CTestDlgDll();
};


//////////////////////////////////////////////////////////////////////////
extern "C" MYDLG_API void CreateMyDlg(HWND hWnd);
extern "C" MYDLG_API void CloseMyDlg(void);

#endif //__MYDLG_H__

and the implementation:

// TestDlgDll.cpp : Defines the entry point for the DLL application.
//
#include "stdafx.h"
#include "TestDlgDll.h"
#include "TestDlg.h"
CTestDlg *m_pMyDlg;
//////////////////////////////////////////////////////////////////////////
// you should put the following code into you new dll.
//////////////////////////////////////////////////////////////////////////
extern "C" MYDLG_API void CreateMyDlg(HWND hWnd);
extern "C" MYDLG_API void CloseMyDlg(void);
CTestDlgDll* gpThisDLL;
MYDLG_API void CreateMyDlg(HWND hWnd)
{ 
    gpThisDLL->CreateMyDialog(hWnd);
}
MYDLG_API void CloseMyDlg()
{ 
    gpThisDLL->CloseMyDialog();
}
CTestDlgDll::CTestDlgDll()
{ 
    gpThisDLL = this;
    m_pMyDlg = NULL;
}
CTestDlgDll::~CTestDlgDll()
{
    CloseMyDialog(); 
}
void CTestDlgDll::CreateMyDialog(HWND hWnd)
{
    AFX_MANAGE_STATE(AfxGetStaticModuleState());
    
    if(m_pMyDlg == NULL)
    { 
        CWnd *pParent = CWnd::FromHandle(hWnd);
        m_pMyDlg = new CTestDlg(pParent);
        m_pMyDlg->Create(IDD_TESTDLG, pParent); 
        m_pMyDlg->ShowWindow(SW_SHOW); 
    } 
}
void CTestDlgDll::CloseMyDialog()
{
    AFX_MANAGE_STATE(AfxGetStaticModuleState());
    
    if(m_pMyDlg != NULL)
    { 
        m_pMyDlg->DestroyWindow();
        delete m_pMyDlg; 
        m_pMyDlg = NULL;
    } 
}

The EXE(?) Implementation

//API type list (from dll)
typedef void (*PFnCreateMyDialog)(HWND hWnd);
typedef void (*PFnCloseMyDialog)(void);
HMODULE hDLL = NULL;
void CMainFrame::OnMydialogOn() 
{
    // TODO: Add your command handler code here
    if(hDLL == NULL)
    {
        CString dllPath = "";
        CFileDialog dlg(
        TRUE, 
        NULL, 
        NULL, 
        OFN_FILEMUSTEXIST | OFN_OVERWRITEPROMPT | OFN_PATHMUSTEXIST, 
        _T("dll files|*.dll|"), 
        AfxGetMainWnd());

    if( dlg.DoModal() == IDOK)
    {
        //get the dll path
        dllPath = dlg.GetPathName();
        //////////////////////////////////////////////////////
        // load library
        hDLL = LoadLibrary(dllPath);
        if( hDLL == NULL)
        {
            AfxMessageBox("LoadLibrary Error !!");
            return;
        }

        PFnCreateMyDialog pFnCreate = 
          (PFnCreateMyDialog)GetProcAddress(hDLL, "CreateMyDlg");

        if( pFnCreate == NULL)
        {
            FreeLibrary(hDLL);

            AfxMessageBox("Get API - Error !!");
            return;
        }

        //Pass the window handle to dll
        (pFnCreate)(this->GetSafeHwnd());
    } 
   }
   else
   {
    if(hDLL)
    {
        PFnCloseMyDialog pFnClose = 
          (PFnCloseMyDialog)GetProcAddress(hDLL, "CloseMyDlg"); 
        (pFnClose)();
        FreeLibrary(hDLL); 
        hDLL = NULL;
    } 
   }

}