Re: Single Document MDI-like interface questions

Mikel <>
Fri, 24 Jul 2009 00:31:45 -0700 (PDT)
On 23 jul, 20:31, Joseph M. Newcomer <> wrote:

See below...

On Thu, 23 Jul 2009 14:10:43 +0200, "Mikel" <mikel.luri_NOSPAM@gmail_NOSP=> wrote:

Hi all:

I'm creating a single-document MDI-like application. You know, several
different views on a single document, in an MDI framework.
I'd like it to have a CFormView as a main view, where the user can set s=


"Project" settings and from which the user can open the other views.

So far, I've created the CFormView MDI app, and changed the "new documen=


handling mechanism to close the current document and open a new one, so =


only one document (and one FormView) is open at any time. I've also adde=


two views, and by following Joe's example in

, I

can open them via a menu handler:

void CMainFrame::OnOpenGreenView()

void CMainFrame::OpenGreenView()
   if (pGreenViewTemplate == NULL)
       pGreenViewTemplate = new CMultiDocTemplate(IDR_GreeVie=



       CMyDoc* doc = (CMyDoc*)GetCurrentDocument();
       CFrameWnd* frame = pGreenViewTemplate->CreateNewFrame(=

doc, NULL);

       if (frame != NULL)
           frame->InitialUpdateFrame(doc, TRUE);

I have the same for the other view, say RedView.

Now, how can I handle the situation where the user closes the view and l=


tries to open it?

Closes which view?
****>Right now it doesn't open, because the MultiDocTemplate is not destr=


The point of the code is that the MultiDocTemplate is not *supposed* to b=

e destroyed, at

least not until the CMainFrame::OnDestroy or CMainFrame::~CMainFrame hand=

ler. THe whole

point of the code is that it may or may not already exist, but if it does=

n't it is created

at the point where it is first needed, and retained until the program ter=

minates. So you

can't say "it doesn't open because the MultiDocTemplate is not destroyed"=

.. It may not

open for some OTHER reason (that's why single-stepping was invented in th=

e debugger) but

it is *not* because the template is not destroyed! The template should=

 be created ONCE. I

just chose to not bother to create it until it was needed.
****>I've thought of posting a message to the MainFrame when the ChildFra=

me is

destroyed, so it can destroy the CMultidocTemplate and set it to NULL.

That would be a mistake. There is no REASON to destroy the template, a=

nd in any case, you

must not.destroy it because it must exist!

idea I've come across is to hide or minimize the ChildFrame instead of
destroying it and when the user tries to open it again, restore it, but =


not really sure how to do this.

No, this would be wrong. When you destroy the view, you *want* the chi=

ld frame to be


Another problem is I don't know how to switch to an open view. For examp=


the three views are open and maximized, the active one is the FormView, =


the user clicks on "open the GreenView". I'd like it to switch to the on=


that's already open.

That case is simple. You just get the current active document, and cal=

l its method

ActivateView(RUNTIME_CLASS(CGreenView)). Since you have made sure you =

have only one

instance of each view, you define this as

BOOL CMyDocument::ActivateView(CRuntimeClass * act)
    { /* scan views */
     POSITION pos = GetFirstViewPosition();
     while(pos != NULL)
         CView * view = GetNextViewPosition(pos);
         if(IsKindOf(view, act))
            { /* found it */
             CMDIChildWnd * wnd = (CMDIChildWnd *)view->G=


             return TRUE;
           } /* found it */
        } /* scan views */
     return FALSE;

Now when you come in to the CreateGreenView handler in the main frame, yo=

u first call

GetActiveDocument(). If this returns NULL, you are in trouble, since t=

he menu item should

not have been activated and you shouldn't be here. If it is non-NULL, =

you would call the

ActivateView(RUNTIME_CLASS(GreenView)); if it returns TRUE, the view exis=

ts and has been

activated; if it returns FALSE, you create the view.

I guess I have to get the ChildFrame from the
CMultiDocTemplate and activate it, but I don't know how to do it, as thi=

s is

my first incursion in the MDI world.

I wouldn't deal with the template; I'd have the document worry about it.

And the last, for now: I'd like to open the "Green" and "Red" views in
response to button clicks in the form view, instead of (or in adition to=


menu commands. How should I do this? Send a message to the MainFrame in =


button handler, maybe?

In this case, I would have the CFormView do as you describe; send a user-=

defined message,

such as UWM_ACTIVATE_VIEW, which contains the RUNTIME_CLASS of the view i=

n its WPARAM or

LPARAM. Then some simple if-tests and call the appropriate OnXXXXView =



Thanks in advance for your patience. As I said, I'm new to MDI.


Joseph M. Newcomer [MVP]
MVP Tips: Ocultar texto de la cita -

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Thanks, Joe. What you suggest is, more or less, what I ended up doing,
and it is working fine.
Now I have a solution, I see that what I was trying to do was quite
silly. Anyway, thanks

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