win32 MDI client form not updating its size

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C++

Windows

Win32

API

MDI

Hi Friends

I have created a MDI form in that i have 2 forms (treeview form and information form)
in 2nd (information form)
i have added 2 buttons next and previous

minimize, maximize works on all of client form correctly(before any click on 2nd form)


Problem:
when i click button on the info form or click the info form and maximize my application
my client window do not change its size


in client form 2 wndproc (also i have changed form 2 size in mainwindow wndproc)

case WM_CREATE:
{
	InitCommonControls();
	CREATESTRUCT *cs=reinterpret_cast<createstruct*>(lParam);			
	int desktopwidth=GetSystemMetrics(SM_CXSCREEN);

	hp_L = CreateWindowEx(WS_EX_CLIENTEDGE,_T("button"),_T("<"),WS_CHILD|WS_CLIPCHILDREN|WS_VISIBLE,0,0,30,PICBOX,hwnd,(HMENU)ID_CHLDWND_PREV,cs->hInstance,0);
	hp_R = CreateWindowEx(WS_EX_CLIENTEDGE,_T("button"),_T(">"),WS_CHILD|WS_CLIPCHILDREN|WS_VISIBLE,desktopwidth-30,0,30,PICBOX,hwnd,(HMENU)ID_CHLDWND_NEXT,cs->hInstance,0);
	hpbox   = CreateWindowEx(WS_EX_CLIENTEDGE,_T("static"),_T(""),WS_CHILD|WS_CLIPCHILDREN|WS_VISIBLE,0,0,0,0,hwnd,(HMENU)ID_CHLDWND_DASH,cs->hInstance,0);
	return 0;
}


case WM_SIZE:
	if (wParam==SIZE_MAXIMIZED)
	{
		SetWindowLongPtr(hpbox,GWL_EXSTYLE,0);
		SetWindowLongPtr(hp_L,GWL_EXSTYLE,0);
		SetWindowLongPtr(hp_R,GWL_EXSTYLE,0);
	}
	else
	{
		SetWindowLongPtr(hpbox,GWL_EXSTYLE,WS_EX_CLIENTEDGE);
		SetWindowLongPtr(hp_L,GWL_EXSTYLE,WS_EX_WINDOWEDGE);
		SetWindowLongPtr(hp_R,GWL_EXSTYLE,WS_EX_CLIENTEDGE);
	}
	MoveWindow(hpox,0,0,LOWORD(lParam),HIWORD(lParam),true);
	MoveWindow(hp_L,0,0,30,PICBOX,true);
	MoveWindow(hp_R,0,0,LOWORD(lParam),HIWORD(lParam),true);

Thanks;