mfc access to formview item from dialog box

Question

In my SDI application i need to get this behawiour. After I click on a button on the FormView, a CDialog opens. When I press the OK button on the CDialog, I call a function of the FormView. I don't want to close the CDialog. I try to do it with modeless dialog, but when i call formview function from dialog, i can't access to formview's control, like it's lost hwnd; the error is can't read memory of m_hwnd, the hwnd is ???. This is my code: Open modeless dialog:

CCampiDlg *m_pDialog = NULL;
HWND hCampi = NULL;

// Invoking the Dialog
m_pDialog = new CCampiDlg;

if (m_pDialog != NULL)
{
    BOOL ret = m_pDialog->Create(m_pDialog->IDD, this);
    if (!ret)   //Create failed.
    {
        AfxMessageBox(_T("Error creating Dialog"));
    }
    m_pDialog->ShowWindow(SW_SHOW);
}

when i press the ok button in the dialog i do:

CEditorTxView pView;
box2 = (CEdit*)(GetDlgItem(IDC_CAMPI_BOX2));
box2->GetWindowTextW(campo);
pView.inserisciCampo(1, campo);

In inserisciCampo function in CEditorTxView (CFormView) i have to do operation with my control txtCtrl, but it's lost hwnd. The declaration of txtCtrl is in the CEditorTxView.h

CTx1 txtCtrl;

And initialize it in DoDataExchange function:

void CEditorTxView::DoDataExchange(CDataExchange* pDX)
{
    CFormView::DoDataExchange(pDX);
    DDX_Control(pDX, IDC_TX1, txtCtrl);
}

Someone can help me plz?

MikMik MikMik · Accepted Answer · 2012-10-15T10:17:40

I can give you two answers here:

How to do what you are asking (get access to a control of the CFormView from a modeless dialog)
How to solve your underlying problem (communicate changes in a modeless dialog to the owner view)

For the first one, you have to declare a pointer to the view in the dialog class and initialize it in the constructor of the view:

class CCampiDlg : public CDialog
{
public:
    CCampiDlg(CEditorTxView* pView,  CWnd*pParent = NULL) // Change declaration to add pointer to view
    : m_pView(pView)
    {
    }
// ... Whatever
private:
    CEditorTxView* m_pView;
}

Now in your button handler:

CEdit* box2 = (CEdit*)(GetDlgItem(IDC_CAMPI_BOX2)); // Why not use a control variable?
box2->GetWindowTextW(campo);
m_pView->inserisciCampo(1, campo);

This should do what you are asking for. However, it is the wrong way to do it.

The problem with this approach is that the dialog knows way too much about its parent. It knows it is of type CEditorTxView and that it has a member called inserisciCampo, that takes a number and some text.

It shouldn't know that much. In fact, knowing anything about it, other than it is of type CView or even CWnd, is too much.

If the dialog knows about the view, you can't reuse the dialog with other views, and anytime the view changes its representation (what now is a textbox may be a combobox in the future, for example) the dialog must change accordingly.

The solution would be to send a message to the parent, explaining what's happened. Then the parent (the view) should know haw to handle that event. For example:

class CCampiDlg : public CDialog
{
public:
    CCampiDlg(CWnd*pParent = NULL) {}
protected:
    OnOk()
    {
        CString campo;
        c_CampiBox2.GetWindowText(campo);
        GetParent()->SendMessage(UWM_CAMPO2_SET, 0, (LPARAM)&campo);
    }
}

In the view:

// It can be ON_REGISTERED_MESSAGE:
ON_MESSAGE(UWM_CAMPO2_SET, OnCampo2Set)

//...    

LRESULT CEditorTxView::OnCampo2Set(WPARAM, LPARAM lParam)
{
    CString* s = (CString*) lParam;
    inserisciCampo(1, *campo);
    return 0;
}

Now, you have decoupled the view and the dialog. The dialog knows nothing about the view. You can change its type, change the representation, even make it a dialog, and you don't have to change anything in the dialog. And if you need that same modeless dialog somewhere else, you just drop it there, create a message handler in the parent, and voilà!

For further explanations and better examples, check these articles:

Dialog and control design (Your case is explained in the section "Notifications to the environment")
Message management

mfc access to formview item from dialog box

2 Answers