DOCUMENT:Q108587 07-MAY-2001 [visualc]
TITLE :HOWTO: Get Current CDocument or CView from Anywhere
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:1.0,2.0,2.1,4.0,4.1
OPER/SYS:
KEYWORDS:kbDocView kbMFC kbVC kbDSupport kbGrpDSMFCATL
======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), used with:
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 4.1
-------------------------------------------------------------------------------
SUMMARY
=======
In a Microsoft Foundation Classes (MFC) Windows-based application, it is often
useful to be able to get a pointer to the currently active document or view from
anywhere in the program. For example, being able to access the current document
from a dialog box is sometimes useful. This article discusses the simplest
methods for doing so, using the relationships between MFC objects, and basic MFC
architecture.
MORE INFORMATION
================
One of the cases where you might need a pointer to the currently active view or
document is in a modal or modeless dialog box. Generally, a dialog box should be
created by the view class, because the view is what deals with the application's
user interface.
Because the view class is creating the dialog box, it can pass a pointer to
itself, or the active document [obtained with the GetActiveDocument() function]
to the dialog box. This could be done through the dialog box's constructor or
some other member function. For modal dialog boxes, the view could also put data
from the dialog box into the document when DoModal() returns.
These methods are generally preferable to relying on generic functions to return
pointers to the currently active view or document.
To allow you to get a pointer to the currently active document from anywhere in
the program, add a static member function to your CDocument derived class as
follows:
Edit the document's header file as follows to add a static member function,
GetDoc():
// Document header file
class CMyDoc : public CDocument
{
...
public:
static CMyDoc * GetDoc();
...
};
For a single document interface (SDI) application, add the following code to your
SDI document's implementation file for CMyDoc::GetDoc():
// SDI document implementation file
CMyDoc * CMyDoc::GetDoc()
{
CFrameWnd * pFrame = (CFrameWnd *)(AfxGetApp()->m_pMainWnd);
return (CMyDoc *) pFrame->GetActiveDocument();
}
For a multiple document interface (MDI) application, the CMyDoc::GetDoc() code
should be the following:
CMyDoc * CMyDoc::GetDoc()
{
CMDIChildWnd * pChild =
((CMDIFrameWnd*)(AfxGetApp()->m_pMainWnd))->MDIGetActive();
if ( !pChild )
return NULL;
CDocument * pDoc = pChild->GetActiveDocument();
if ( !pDoc )
return NULL;
// Fail if doc is of wrong kind
if ( ! pDoc->IsKindOf( RUNTIME_CLASS(CMyDoc) ) )
return NULL;
return (CMyDoc *) pDoc;
}
To allow you to get a pointer to the currently active view from anywhere in the
program, add a static member function to your CView derived class as follows:
Edit the view's header file as follows to add a static member function,
GetView():
// View header file
class CMyView
{
...
public:
static CMyView * GetView();
...
};
For an SDI application, add the following code to your SDI view's implementation
file for CMyView::GetView():
// View implementation file
CMyView * CMyView::GetView()
{
CFrameWnd * pFrame = (CFrameWnd *)(AfxGetApp()->m_pMainWnd);
CView * pView = pFrame->GetActiveView();
if ( !pView )
return NULL;
// Fail if view is of wrong kind
// (this could occur with splitter windows, or additional
// views on a single document
if ( ! pView->IsKindOf( RUNTIME_CLASS(CMyView) ) )
return NULL;
return (CMyView *) pView;
}
For an MDI application, the CMyView::GetView() code should be the following:
// MDI view implementation file
CMyView * CMyView::GetView()
{
CMDIChildWnd * pChild =
((CMDIFrameWnd*)(AfxGetApp()->m_pMainWnd))->MDIGetActive();
if ( !pChild )
return NULL;
CView * pView = pChild->GetActiveView();
if ( !pView )
return NULL;
// Fail if view is of wrong kind
if ( ! pView->IsKindOf( RUNTIME_CLASS(CMyView) ) )
return NULL;
return (CMyView *) pView;
}
Now, from anywhere in your program, where the document or view header files have
been included, you can call:
CMyDoc::GetDoc();
- Or -
CMyView::GetView();
to get a pointer to the currently active document or view, respectively. These
functions return NULL if there is no active document or view.
Note that a pointer to the application's CDocument or CView derived class is
returned, not just a generic CDocument or CView pointer. This allows you to
access members specific to your new class. The MDI versions of these functions,
and the SDI version of the GetView() function, will use run-time type checking
to verify that the document or view is of the correct class.
REFERENCES
==========
For more information on this subject, and on the member functions used, please
see:
Visual C++ 1.0 and Visual C++ for Windows NT "Class Library Reference, Volume I,"
page 35, "Relationships Among Documents, Views, Frame Windows, Templates, and
the Application."
CFrameWnd documentation in the same manual.
Additional query words: kbSweptVC600
======================================================================
Keywords : kbDocView kbMFC kbVC kbDSupport kbGrpDSMFCATL
Technology : kbAudDeveloper kbMFC
Version : winnt:1.0,2.0,2.1,4.0,4.1
Issue type : kbhowto
=============================================================================
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.
Copyright Microsoft Corporation 2001.