;  GUI_GUI.au3  V00.00.01   6 Mar 2017 08:50

#include <GuiConstants.au3>
#include <WindowsConstants.au3>
#include <WinAPI.au3>
#include <MenuConstants.au3>
#include <TabConstants.au3>
#include <ColorConstants.au3>

  $Main_GUI = GUICreate("Main", 500, 500)
  GUISetBkColor(0x1B5583, $Main_GUI) ;
  GUISetState(@SW_SHOW, $Main_GUI)

$Child1_GUI = GUICreate("ExitGUI", 480, 480, 10, 10, $WS_CHILD, -1, $Main_GUI)
 $Btn_Exit = GUICtrlCreateButton("E&xit", -1, -1, 90, 20) ; note "&" syntax! Underscores next char
 GUICtrlSetColor($Btn_Exit, $COLOR_RED) ; sets text colour
; this displays the 'master' GUI..
GUISetState(@SW_SHOW, $Child1_GUI)

; this sets up the 'child' GUI..
$Child2_GUI = GUICreate("Child", 200, 100, 10, 50, $WS_CAPTION)
GUISetBkColor(0xfffaf0, $Child2_GUI)
$Btn_Test = GUICtrlCreateButton("Test", 10, 10, 90, 20)
; this displays the 'child' GUI but not yet positioned...
GUISetState(@SW_SHOW, $Child2_GUI)
; this puts the 'child' GUI within 'master' GUI...
DllCall("user32.dll", "int", "SetParent", "hwnd", WinGetHandle($Child2_GUI), "hwnd", WinGetHandle($Child1_GUI))
;sleep(5000)
;Exit

While 1
    $msg = GUIGetMsg()
    Switch $msg
        Case $GUI_EVENT_CLOSE ;, $Btn_Exit ;not work without $Btn_Exit defined!
            Exit
        Case $Btn_Test
            MsgBox(0, "Test", "Hit Button on Child Window")
    EndSwitch
WEnd