control flicker when I use double buffering to avoid window flicker

"Fuquan.Ko" <>
Thu, 28 Apr 2011 01:19:49 -0700 (PDT)
    Now i need to draw some graphics on the entire
dialog ......also ,on the dialog i have some drag Bars(for
    I use double buffer to avoid the dialog flicker ,do something like
  1. CRect rect;
    CBitmap *pOldBmp=m_memDC.SelectObject(&m_memBmp);
        //.........draw graphics into memDC...



2. override the OnEraseBkgnd function ,just to return TRUE;

With the two steps above ,the dialog's flickering can be avoided..
 ...but when i drag the button to move ,the button flickers....

is there anyway to solve this problem?

thanks for any reply

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From: Dani Peer <>
Subject: Re: CEdit does not get WM_CHAR in a DLL when the main application is minimized
Date: Tue, 31 May 2011 09:32:35 -0700 (PDT)
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On May 31, 7:15 pm, Joseph M. Newcomer <> wrote:

See below...

On Tue, 31 May 2011 07:45:59 -0700 (PDT), Dani Peer <> =


I have a simple application that lunch a DLL. The DLL opens a window
with a splitter of 2 CFormView and each one of the forms there is an

Note that applications do not "launch" DLLs. They merely use them. =

 Or, as you indicate

below, dynamically load them.
****>The code is as following:

void CTest002View::OnBnClickedButton2()

You really have to stop using the stupid names that VS assigns to control=

s and change the

names to something that has meaning.

 HINSTANCE hDLL; // Handle to DLL
 hDLL = LoadLibrary("SessionWindow.dll");

Might as well start programming Unicode-aware. It is a good habit to d=

evelop. Stop

thinking that 8-bit characters are useful.
****> if (hDLL == NULL)


This is silly. If the hDLL is NULL, there is no possible way you can c=

all FreeLibrary on

a NULL handle. Note that what you wrote here is
        if(hDLL == NULL)
which does not make sense
****> else

    typedef BOOL (CreateObject3)();
    CreateObject3* pCreateObject3 = (CreateObject3
*)GetProcAddress(hDLL, "CreateObject3");

It might be really, really useful here to see if pCreateObject3 is NULL b=

efore trying to

use it...

Note that GetProcAddress is the *only* API that uses 8-bit only character=

s, so using _T()

around the second argument would actually be incorrect. But this is ju=

st about the only

exception to using _T() you will encounter, except in very rare and exoti=

c situations.

****> BOOL bRet = (pCreateObject3)();

You do not need to put pCreateObject3 in parentheses; you can write
        BOOL bRead = pCreateObject3();
***> }


The method in the DLL is as following:
extern "C" __declspec(dllexport) BOOL CreateObject3()
 SessionFrame2* pSessionFrame2 = new SessionFrame2;
 pSessionFrame2->Create(NULL, _T("Session Frame"),
WS_OVERLAPPEDWINDOW , CRect(20, 20, 400, 400), NULL, NULL,

I'm not sure what the totally random numbers 20, 20, 400, 400 could possi=

bly mean. If you

care about window sizes, you will compute them dynamically based upon oth=


characteristics of the screen, its resolution, the parent frame size, etc=

.. There is no

way these values can have meaning other than on one machine with one curr=

ent default font,

a particular graphics card, a particular screen resolution, a particular =

version of the

device driver for the card, and a particular display screen.
****> pSessionFrame2->ShowWindow(SW_SHOWNORMAL);

 return TRUE;

Everything works fine, and when I minimized the main application I
still can type on the edits in the dll.
But, when I'm adding the method
I can not type on the edits in the DLL when I minimized the

What is SessionFrame2 derived from; I can't tell what Create means unless=

 I know the class

of the object being created. However, I'm guessing from the name it mi=

ght be a class

derived from CMDIChildWnd, in which case the fifth parameter is the paren=

t window which

you have specified as NULL, which means the parent is supposed to be the =

main application

window. In this case, if you minimize the application, the frame windo=

w you just created

should disappear as well. The fact that it does not means that I may h=

ave guessed wrong

about the class this is derived from.

Note that I have no idea about what AFX_MANAGE_STATE does to the ability =

to find the main

application window, but if this SessionFrame2 class really is derived fro=

m CMDIChildWnd,

the first thing I'd do is start single-stepping to see what the parent AC=


computed as being, or I'd use Spy++ to identify the parent window; it sou=

nds suspiciously

like you have a parent that is the desktop, which allows the window to ig=

nore what happens

to the main frame.

Also, you have not indicated how the edit control is created, or who crea=

tes it; if you

have a CFormView in this view, that would be an interesting fact to know.=

  I'm not sure at

this point it helps, but it would be useful to know.

Note that if the parent of the window is the desktop, then what you are s=

eeing is

*exactly* how it is *supposed* to behave. But I suspect that you do no=

t want the parent

of the window in question to be to the desktop, but to be the main applic=

ation frame.


Any idea ?
-- Dani

Joseph M. Newcomer [MVP]
MVP Tips:

1. SessionFrame2 derived from CFrameWndEx.
2. The Edit are created as part of the CFormView resources.

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