Why the ui keep flicker

I have a project which have three dialog, Let's say A, B, C. And A
contain B & C, B contains C. They all are inherited from a DialogBase
class and have a setBitmap function to set a background image.

And I have add the relationship that every time drag on C, B will drag
as well. and B is a transparent dialog!

When onLbuttonDown is triggered, I will set this m_pParent-
>ModifyStyleEx(0, WS_EX_TRANSPARENT); which make that the B dialog is

transparent.

The problem is : if i set this, the dialog B is transparent, but when
I move the B, it will keep flicker.

But if i comment m_pParent->ModifyStyleEx(0, WS_EX_TRANSPARENT); Then
the dialog B will not be transparent, but it will not flicker.

Can someone give me a solution ? Attached is the sample project that have the flicker problem.

Here is a solution to avoid flickering with double buffering:

http://www.codeproject.com/KB/GDI/flickerfree.aspx

Have you ever read my code ?I have used double buffer!

According to Ubuntu there is nothing in your rar file, so I can't look in it, but have you tried disabling the EraseBackground function ?

I uploaded the project again in zip file, Please help me~~