BUTTON_EVENT_Unavailable

[haohaoxuexi1]

#Create main menu object
import vizmenu
menu = vizmenu.add()

#Align the menu in the enter of the top of the screen.
menu.setAlignment( vizmenu.CENTER )

#Scale the menu up
vizmenu.MENU_FONT_SIZE = 24

#Create five menu subjects
n1 = menu.add( 'n1' )
z1 = menu.add( 'z1' )

#Create sub-menu with label for n1
n_checkbox = n1.add( viz.CHECKBOX, 'n11' )
n_checkbox.setScale([3]*3)

#Create sub-menu with label for z1
z_checkbox_p = z1.add( viz.CHECKBOX, 'z11' )
z_checkbox_p.setScale([3]*3)

z_checkbox_n = z1.add( viz.CHECKBOX, 'z12' )
z_checkbox_n.setScale([3]*3)

def onButton_trigger(obj,state):

global z111
global z222

#judgement for z1
if obj == z_checkbox_p:
if state == viz.DOWN:
z111 = True
print 'zt1=',z111
else:
z111 = False

#judgement for z2
if obj == z_checkbox_n:
if state == viz.DOWN:
z222 = True
print 'zt2=',z222
else:
z222 = False
viz.callback(viz.BUTTON_EVENT, onButton_trigger)

def onButton_trigger2(obj,state):

global n11

#judgement for z1
if obj == n_checkbox:
if state == viz.DOWN:
n11 = True
print 'n11=',n11
else:
n11 = False

viz.callback(viz.BUTTON_EVENT, onButton_trigger2)

Why is the code only valid for the later viz.BUTTON_EVENT? But not both of them?