I want to write an "InputBox" that I can reuse many times throughout many
projects. The usage will be something like:

double myVal = GetValidDouble(sPrompt, dDefaultValue)

This function will dynamically construct a dialog box (no templates
involved - too much maintenance and clutter) which has a static text control
for the prompt and an edit box for input. I have managed to construct the
dialog box dynamically OK. The problem I have is that I want to subclass the
edit box to a new class that I've written which validates the input as the
user types. The code goes something like this:

1) Call the function.
2) The function creates a class which builds a new dialog in memory and also
has a member variable(m_edt) corresponding to the CEditDouble derived class.
This variable is a  class member. It adds the static and the (standard) edit
box with IDs which I know.
3) in the InitDialog function of the dynamically built dialog class I have
the following code:

 m_edt.SubclassDlgItem(IDC_EDTDOUBLE, this);

This produces an assert from within CWnd::Attach(HWND hWndNew):

ASSERT(FromHandlePermanent(hWndNew) == NULL);

I looked in this function and find:
CWnd* Pascal CWnd::FromHandlePermanent(HWND hWnd)
{
 CHandleMap* pMap = afxMapHWND();
 CWnd* pWnd = NULL;
 if (pMap != NULL)
 {
  // only look in the permanent map - does no allocations
  pWnd = (CWnd*)pMap->LookupPermanent(hWnd);
  ASSERT(pWnd == NULL || pWnd->m_hWnd == hWnd);
 }
 return pWnd;

Going through in debug I notice that the pWnd->m_hWnd==hWnd always seems to
be true and not NULL.

When I try the same code with a dialog box based on a resource template it
works fine. Any clues?

Are you already creating the edit window by calling the CEditDouble
Create function?

Dave
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I wasn't, so I tried that too, this gave an assert in the Attach method of
the CEditDouble.

The good news is that I started looking at the create method and rethinking
the problem. I managed to get the functionality I wanted by simply
creat(Ex)ing the CEditDouble in the InitDialog handler. This seems to create
a new control of the correct class. The bad news is that I still haven't
solved the "how to subclass" problem.

Thanks for your time so far,

martin