SubclassWindow Question

I want to experiment with the SubclassWindow() function and here is what I did:

- Create a dialog based MFC app with a textbox (mapped to member variable m_myedit)

- Created a class CSubWnd derived from CWnd using classwizard. Didn't add any code to the class.

- In my dialog's class added a member CSubWnd m_test;

- In my dialog's OK button handler, add the following code to subclass the textbox's window.

     if(m_test.SubclassWindow(m_myedit.m_hWnd)) {
          AfxMessageBox("succeeded");
     }

I was hoping at least it should return TRUE. But instead, it gave assertion failure. May I know what is wrong here?

Thanks..
onlygoAsked:
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The MasterConnect With a Mentor Commented:

Don't map the textbox to a member variable (remove the variable m_myedit).  Then instead of calling...

m_test.SubclassWindow (m_myedit.m_hWnd)

call...

m_test.SubclassWindow (GetDlgItem (IDC_MYEDIT))

...(replacing IDC_MYEDIT with the dlg item id of your edit control).

Good luck!
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The MasterCommented:

First of all, what's the assertion it's giving you?

Secondly, make sure that you're not calling the base class CDialog::OnOK() function in your OnOK() function.
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onlygoAuthor Commented:
It's in wincore.cpp line 312:
     ASSERT(FromHandlePermanent(hWndNew) == NULL);
     // must not already be in permanent map

I am not calling the base CDialog::OnOK()
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onlygoAuthor Commented:
Thanks! The error is gone now. But it doesnt seem to have any effect after I added the WM_KEYDOWN message handler to my CSubWnd class. I mean I pressed key inside the textbox but my message handler does not seem to run at all. Also, what does the "permanent map" mean?
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The MasterCommented:

MFC keeps a map (a one-to-one relationship table) of window handles to CWnd object pointers.  It's "permanent" in the sense that the CWnd object pointers are not temporary objects.  As soon as the object is destroyed, the handle-to-object relationship is removed from the map.  MFC was just making sure that the window handle wasn't already mapped to a CWnd object before it mapped it to your object.

As for not handling WM_KEYDOWN, I'm not sure about that.  It's been a while since I've used subclassing in MFC.  As far as I know, you should be getting it.  Try adding a handler for WM_CHAR and see if that works.
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The MasterCommented:

MFC keeps a map (a one-to-one relationship table) of window handles to CWnd object pointers.  It's "permanent" in the sense that the CWnd object pointers are not temporary objects.  As soon as the object is destroyed, the handle-to-object relationship is removed from the map.  MFC was just making sure that the window handle wasn't already mapped to a CWnd object before it mapped it to your object.

As for not handling WM_KEYDOWN, I'm not sure about that.  It's been a while since I've used subclassing in MFC.  As far as I know, you should be getting it.  Try adding a handler for WM_CHAR and see if that works.
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The MasterCommented:

MFC keeps a map (a one-to-one relationship table) of window handles to CWnd object pointers.  It's "permanent" in the sense that the CWnd object pointers are not temporary objects.  As soon as the object is destroyed, the handle-to-object relationship is removed from the map.  MFC was just making sure that the window handle wasn't already mapped to a CWnd object before it mapped it to your object.

As for not handling WM_KEYDOWN, I'm not sure about that.  It's been a while since I've used subclassing in MFC.  As far as I know, you should be getting it.  Try adding a handler for WM_CHAR and see if that works.
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onlygoAuthor Commented:
ok thanks for ur help! i think i will go figure out why the WM_KEYDOWN is not working myself. thanks again.
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The MasterCommented:

Wait...I remember now.  Instead of calling SubclassWindow() call SubclassDlgItem().  So your code would look like this...

if (m_test.SubclassDlgItem (IDC_MYEDIT, this)) {
...
}

This will work for you.  And you don't have to worry about calling UnsubclassWindow().

I hope this helps!

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The MasterCommented:

Wait...I remember now.  Instead of calling SubclassWindow() call SubclassDlgItem().  So your code would look like this...

if (m_test.SubclassDlgItem (IDC_MYEDIT, this)) {
...
}

This will work for you.  And you don't have to worry about calling UnsubclassWindow().

I hope this helps!

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The MasterCommented:

Wait...I remember now.  Instead of calling SubclassWindow() call SubclassDlgItem().  So your code would look like this...

if (m_test.SubclassDlgItem (IDC_MYEDIT, this)) {
...
}

This will work for you.  And you don't have to worry about calling UnsubclassWindow().

I hope this helps!

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onlygoAuthor Commented:
works excellently.. thanks
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