Re: EnumChildWindows

=?Utf-8?B?QWw=?= <>
Wed, 24 Oct 2007 19:57:00 -0700
Hi Giovanni Dicanio

I am looking over the code that you sent here and I am trying to figure out
how I can change it to meet my needs. Sorry about the time laps but I am
trying to figure it out too. Here is my code and let me know where I am going
wrong or how I can adapt it to your code if you could

// Declaration
static bool CALLBACK MyWndEnumProc(HWND hWnd, LPARAM lParam);

// The function
bool CALLBACK CMainFrame::MyWndEnumProc(HWND hWnd, LPARAM ppWndLPARAM)
    CWnd* pWndChild = CWnd::FromHandlePermanent(hWnd);
    CWnd** ppWndTemp = (CWnd**)ppWndLPARAM;

    if( pWndChild && pWndChild->IsKindOf(RUNTIME_CLASS(CView)) )
        //any view that is found will work:
        *ppWndTemp = pWndChild; //pass ptr to found CView back to calling function
        return FALSE; //stop enumeration
        *ppWndTemp = NULL;
        return TRUE; //continue enumeration

// The call
CWnd* pWnd;

::EnumChildWindows(m_hWnd, pMyWndEnumProc, (LPARAM)&(pWnd));

<end code>
This initializes the pointer pWnd so later in the code, tests can be done.

I am a little confused with the code that you left me at trying to
initialize the pointer pWnd. If you could enlighten me I would greatly
appreciate it. I am still reading "Beginning MFC Programming" by Ivor Horton.
This here is a little bit of a leep for me.

Just Al

"Giovanni Dicanio" wrote:

"David Lowndes" <DavidL@example.invalid> ha scritto nel messaggio

bool CMainFrame::MyWndEnumProc(HWND hWnd, LPARAM ppWndLPARAM)

Non-static class member methods have an invisible "this" parameter -
so your function won't match the expected callback definition.

Either make your callback method static, or a non-class function.

I would go for the class static method, because I prefer not having global
functions (or at least having as few as possible globals :)

To the OP I would suggest doing something like this:

 - create an enumerator class, whose purpose is to do the enumeration

 - this class exposes a static method, to which the caller passes a pointer
to an enumerator class instance ("this")

 - the static method uses the "this" pointer passed as LPARAM to forward the
call to instance-specific enumerator method

In code:


// Enumerator class for
// ::EnumChildWindows enumeration
class ChildWindowsEnumerator

  // Init


  // The "global" (static) enumerator method,
  // to be passed to Win32 API ::EnumChildWindows.
  // Pass <i>this</i> pointer as lParam.
  // This static method forwards the control to the
  // instance-specific method, using the <i>this</i> pointer.
  static BOOL CALLBACK EnumProc(
    HWND hwnd,
    LPARAM lParam /* this */


  // The instance-specific enumerator method
  // (called by EnumProc)
  BOOL Enumerate( HWND hwnd );

    HWND hwnd,
    LPARAM lParam
    ASSERT( lParam != NULL );

    // Forward call to instance-specific enumerator method
    return ((ChildWindowsEnumerator *)lParam)->Enumerate( hwnd );

    HWND hwnd
    ... Do your enumeration here


To be used like so:


// Instance of enumerator class
ChildWindowsEnumerator enumerator;

// Enumerate using the enumerator object

  // Static enumeration method
  ChildWindowsEnumerator::EnumProc, // maybe wants the &(...) ...

  // Enumerator class instance
  (LPARAM) &enumerator



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