add

cs.x =
 cs.y = 0;
 
 cs.cx =
 cs.cy = 32767;

to PrecreateWindow

Oleg ,It still cant't work!I'm in despair,I hit my keyboard, so my keyboard's space key has been broken yet!
However I found out some examples include this function ,and it seems to work!But there is flicker none the less,
and the flicker beacame lightly only!
//////////////////////////////////////////////////////////// //////////////
LRESULT CChildFrame::WindowProc(UINT message, WPARAM wParam, LPARAM lParam)
{
 if (message == WM_NCPAINT)
 {
  // prevent caption blinking
  return TRUE;
 } 
 return CMDIChildWnd::WindowProc(message, wParam, lParam);
}
//////////////////////////////////////////////////////////// //////////////

I can't understand why GUI_VisualStudio7 didn't include any special line and It works so perfectly!
Is there a method to solve this problem?

//////////////////////////////////////////////////////////// /////////////
In my program:
CMainFrame:
 CXTPTabClientWnd m_MTIClientWnd;
 int CMainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)
 {
  ...
  VERIFY(m_MTIClientWnd.Attach(this));
  ...
 }
CChildFrame:
 BOOL CChildFrame::PreCreateWindow(CREATESTRUCT& cs)
 {
  if( !CMDIChildWnd::PreCreateWindow(cs) )
   return FALSE;

  return TRUE;
 }
 void CChildFrame::ActivateFrame(int nCmdShow)
 {

  nCmdShow = SW_SHOWMAXIMIZED;
  CMDIChildWnd::ActivateFrame(nCmdShow);
 }
 LRESULT CChildFrame::WindowProc(UINT message, WPARAM wParam, LPARAM lParam)
 {
  if (message == WM_NCPAINT)
  {
   // prevent caption blinking
   return TRUE;
  } 
  return CMDIChildWnd::WindowProc(message, wParam, lParam);
 }

Thank you again,Oleg!

 Additional add

void CChildFrame::ActivateFrame(int nCmdShow)
{
 // first window should be maximized
 if (GetParent()->GetWindow(GW_CHILD) == this)
 {
  nCmdShow = SW_SHOWMAXIMIZED;
 }
 
 CMDIChildWnd::ActivateFrame(nCmdShow);
}

to make it Maximized by default.

In  GUI_Visualstudio7  .Attach called with bEnableGroups = TRUE

VERIFY(m_MTIClientWnd.Attach(this, TRUE));

Hi,Oleg I have to say that it doesn't work!

However some examples such as GUI_Visualstudio7 don't include these lines ,but it works very well!

Why?

You can create child like this:

BOOL CChildFrame::PreCreateWindow(CREATESTRUCT& cs)
{
 // make sure view is maximum size to eliminate
 // flicker when switching tabs.
 cs.x =
 cs.y = 0;
 
 cs.cx =
 cs.cy = 32767;
 
 // TODO: Modify the Window class or styles here by modifying
 //  the CREATESTRUCT cs

 if( !CMDIChildWnd::PreCreateWindow(cs) )
  return FALSE;

 return TRUE;
}

I found  some examples work very well,but my not!

////////////////////////////
 CXTPTabClientWnd m_MTIClientWnd;
///////////////////////////
int CMainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
 ....

 VERIFY(m_MTIClientWnd.Attach(this));
 
 ....

}
///////////////////////////

Thanks in advance!