Re: recreate a window

".rhavin grobert" <>
Tue, 11 Nov 2008 05:51:17 -0800 (PST)
On 10 Nov., 20:43, Joseph M. Newcomer <> wrote:

See below...
On Mon, 10 Nov 2008 10:26:29 -0800 (PST), ".rhavin grobert" <cl...@yahoo.=

de> wrote:

On 10 Nov., 18:59, Joseph M. Newcomer <> wrote:

See below...

On Mon, 10 Nov 2008 08:09:56 -0800 (PST), ".rhavin grobert" <cl...@yah=> wrote:

a CComboBox and CQControl derived control shall recreate itself, if
the styles given in resource not match the style required for toe
control (here: CBS_OWNERDRAWFIXED must be set). As CComboBox is unabl=


to correctly modify this style with ModifyStyle(), the recreation is
called and works.

The error is that you did not do this at design time. Essentially, =

I treat the failure to

have the wrong styles as an error. Not sure why you are bothering t=

o work around a bug

that shouldn't exist. If this happens, you ASSERT and then fix the =

dialog at design time,

and omit ALL the code below.
CComboBox is not *supposed* to be able to modify this style after the =

control is created,

so it is not "unable to correctly modify this style" because it was ne=

ver defined that

this is even possible.

thats why i recreate it.

My point is, a program which has one of these which is NOT defined as CBS=


is an erroneous program, so you fix it in the dialog template once, and n=

ever again worry

about it.

if there's no way to let my code correct the error, i'd assert. but i
thought to use this flags myself, e.g. recreate a control with the
appropriate windowsflags needed for the control, and use the user-
defined flags for my own implementation (in this case, calling a user-
defined drawing routine instead of my own default drawing routine.)



// recreate the underlying hwnd to match required styles
bool CQControl::QRecreateWindow(DWORD dwStyle, DWORD dwStyleEx)
   CWnd* pWnd = CWnd::FromHandlePermanent(m_hwnd);

This is unnecessary; 'this' is already the CWnd *. So there is no n=

eed for the above


no it is not. 'this' is a CQControl that has no CWnd as baseclass! for
example, the
CQComboBox is a public CComboBox, public CQControl.

That's a different question than the one you asked. You did not specif=

y that you are

using multiple inheritance.

i did'nt say i'm not using it;-) But you're right, assuming direct(?)
inheritance is the default.

But in that case, FromHandle is sufficient.

i just wanted to be shure.

****> ASSERT(pWnd != NULL);

   ASSERT(pWnd == CWnd::FromHandle(m_hwnd));
   if (pWnd == NULL)
           return false;

The above statements are meaningless. You already have 'this' or yo=

u wouldn't be here. It

doesn't matter about what map it is in; you shouldn't care, either.

see above.

You have to provide *all* relevant information in order to get a correct =



Note that I use this technique rather often to create a control in a s=

pace formerly

occupied by a CStatic, so I'm changing the entire control type. Thi=

s code is FAR too

complicated for such a simple task.

a static in Dialog-Editor would not look like a combobox.

   CRect rc;
   HWND hParent = GetParent(m_hwnd); =

  // [1]

CWnd * parent = GetParent();

wrong. see above.

If you use multiple inheritance, a previously unstated case, then yes. =

 But you can't ask

a question without giving all relevant information and expect to get a re=

levant answer


   // get position and size of current window
   GetWindowRect(m_hwnd, &rc); =

                      // [2]

I'm surprised this even compiles. There is no need to use the raw H=

WND. You could just

have written
and get everything you need.

see above;-)

   // following fn's need width and size, we recycle rc
   rc.right = rc.Width(); =

    // [3]

   rc.bottom = rc.Height(); =

                                   // [=

This code is incorrect. You must not set the right and bottom in th=

is fashion, because

you are working with the window rect, and the width and height are ind=

ependent of the

coordinate system. Lose the two assignments above.

   // translate into parents coordinates
   ScreenToClient(hParent, &rc.TopLeft()); =

             // [5]

Why are you not doing something as simple as
                CRect rc;
this is all you need. You have a complex and convoluted solution to=

 a simple problem.

Just translating the top/left coordinate makes no sense, because it wi=

ll produce a window

that has the wrong size.

no. everything works pretty well. i you insist, one could of course
define a struct RECT_ that has let, top, width and height members, but
apart from that, my way is completely ok.

Why do you need to define a new structure? You can just do
        CRect rc;
        ::GetWindowRect(m_hWnd, &rc);
        ::ScreenToClient(parent, &rc);
where, now that I know you are using multiple inheritance, is still simpl=

er than the

complex code you wrote. And by setting the right and bottom to the Wid=

th() and Height(),

BEFORE transforming the top and left, you still get the wrong size.

=E4hm, no.. both rects are in pixel.

You have five overly complicated lines doing what two trivial lines wi=

ll accomplish.


   // let derived class modify rc

I have no idea what this does because there is no handler called OnCre=

ationRect and you

have not given the code for this, but there's nothing I know that need=

s to be done to this

rectangle once you have it.

in this case, the derived class uses this virtual as following:

void CQComboBox::OnCreationRect(RECT& rc)
   RECT rcDropped;
   rc.bottom = rcDropped.bottom -;

Using the 'On' prefix, which is used for handlers, is confusing. Calli=

ng it something

meaningful like ComputeDroppedRect might have made it less ambiguous as t=

o what was going


   // create a new window at current windows coordinates
   HWND hNew = CreateWindowEx(dwStyleEx, QGetClassName(), "", =


           rc.left,, rc.right, rc.bottom, hParent=

, 0,

           ::AfxGetInstanceHandle(), NULL);

Why are you using the raw CreateWindowEx call? You can do this triv=

ially in MFC:

        CWnd temp;
                temp.CreateEx(dwStyleEx, QGetClassName=

(), _T(""), dwStyle, rc,

                        GetDlgCtrlId(), parent=


Note how simple this is. For that matter, does CQControl have a Cre=

ate method that would

be better?

I have no idea why you have chosen to change the control ID by setting=

 it to 0; this kills

off all your handlers in the parent window. For a brief moment you =

will have two controls

with the same ID, but this will be changed momentarily, and causes no =


oh, i thought it was hMenu.

Note that it is specified as being the hMenu for a top-level window and t=

he control ID for

a child window. From the documentation:

"For a child window, hMenu specifies the child-window identifer, an integ=

er value..."

It will have to be cast to an HMENU to satisfy the compiler.

But what you didn't do was make sure it is in the right place in the Z=


        temp.SetWindowPos(this, 0, 0, 0, 0, SWP_NOMOVE | SWP_N=



All this use of raw API and HWNDs is unneccessay.

   // destroy old window and attach new one
   m_hwnd = hNew;

Get rid of all the above lines.

The convoluted nature of what you are doing is probably what leads to =

the assertion

failure. I wouldn't even try to debug this code, I would rewrite it=

 as indicated. Then,

and only then, if there is still a bug, would I worry about it.

Since MFC does not normally support multiple inheritance, there can be so=

me confusing side

effects here that may account for it. What is the type of the object d=

isplayed by the


it displayes the expected type (CQComboBox)

Is there a reason you chose to use multiple inheritance over direct inher=

itance? You are

working in unsupported areas here.

of course;-) i have a baseclass (CQControl) from with CQButton,
CQTree, CQComboBox and so on derive. Each derived class uses multiple
inheritance to derive from CQControl and its MFC-class. By doind this,
i can do the following:

void SomeFunction(CQControl* pCtrl)
    // add an red blinking element with id ELEMENT_ID to the control
    // set text of element ELEMENT_ID with detail id DETAIL_ID to "Some
    // and add an image
    pCtrl->QDtlSet(ELEMENT_ID, DETAIL_ID, _T("Some Text"),
    // Select element ELEMENT_ID

if pCtrl is a CQListView, you set element-row ELEMENT_ID, detail-
column DETAIL_ID to image ELEMENT_IMAGE, detail DETAIL_ID. if pCtrl is
a CQButton and you have more than one element, you get a multibutton.
if you dont have "columns" (Button, ListBox,..), the details appear
tab-separated. So you have the same syntax for all controls. Use in
programm: guess you have a function that shall fill a selection-
control with user-names and some additional infos (an icon per user or
a user-state-color and so on). this function just gets a CQControl*
and fills it. if it fills a Listview, a Treeview, a ListBox, a
ComboBox or even a Button just depents on the design of the GUI. More:
CQControl uses a special worker thread and does all the syncronisation
needed, so you could call the above SomeFunction() from ANY Thread;-)

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