Can't Get my checkbox to check/uncheck

bad_checkbox.py

#!/usr/bin/env python
from kivy.base import runTouchApp
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.checkbox import CheckBox

class NetworkConfig(BoxLayout):

    def __init__(self, *args, **kwargs):
        super(NetworkConfig, self).__init__(*args, **kwargs)

#    def on_checkbox_active(self, checkbox, value):
#        if value:
#            print('The checkbox', checkbox, 'is active')
#        else:
#            print('The checkbox', checkbox, 'is inactive')


widget = Builder.load_string("""
NetworkConfig:
    orientation: 'vertical'
    cols: 1
#    rows: 1
    canvas:
        Color:
            rgba: 0.3, 0.3, 0.3, 1
        Rectangle:
            size: self.size
            pos: self.pos
    Label:
        text: '[b]Network Configuration[/b]'
        markup: True
        size_hint_y: 0.1
        background_normal: None
    GridLayout:
        rows: 8
        padding: dp(8)
        spacing: dp(16)
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 1
            cols: 2
            size_hint_y: 0.9
            Label:
                text: "Host Name"
            TextInput:
                id: hostname
                multiline: False
                hint_text: 'hostname@example.com'
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 2
            cols: 2
            size_hint_y: 0.1
            Label:
                text: 'Automatic setup using DHCP'
            CheckBox:
                id: inet_use_dhcp
                value: True
                active: True
                on_active: root.on_checkbox_active()
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 1
            cols: 2
            Label:
                text: "IP Address"
            TextInput:
                id: inet_address
                multiline: False
                hint_text: '192.168.1.100'
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 1
            cols: 2
            Label:
                text: "Network Mask"
            TextInput:
                id: inet_mask
                multiline: False
                hint_text: '255.255.255.0'
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 1
            cols: 2
            Label:
                text: "Default Gateway"
            TextInput:
                id: inet_bcast
                multiline: False
                hint_text: '192.168.1.1'
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 1
            cols: 2
            Label:
                text: "DNS 1"
            TextInput:
                id: inet_dns1
                multiline: False
                hint_text: 'dns1@example.com'
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 1
            cols: 2
            Label:
                text: "DNS 2"
            TextInput:
                id: inet_dns2
                multiline: False
                hint_text: 'dns2@example.com'
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 1
            cols: 2
            Label:
                text: "DNS 3"
            TextInput:
                id: inet_dns3
                multiline: False
                hint_text: 'dns3@example.com'
""")

runTouchApp(widget)

working_checkbox.py

#!/usr/bin/env python
from kivy.base import runTouchApp
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.checkbox import CheckBox


class NetworkConfig(BoxLayout):

    def __init__(self, *args, **kwargs):
        super(NetworkConfig, self).__init__(*args, **kwargs)

    def on_checkbox_active(self, checkbox, value):
        if value:
            print('The checkbox', checkbox, 'is active')
        else:
            print('The checkbox', checkbox, 'is inactive')

class UseDHCP(CheckBox):
    pass


widget = Builder.load_string("""
NetworkConfig:
    orientation: 'vertical'
    cols: 1
    rows: 1

    Label:
        text: '[b]Network Configuration[/b]'
        markup: True
        size_hint_y: 0.1
        background_normal: None

    GridLayout:
        cols: 1
        GridLayout:
            padding: dp(8)
            spacing: dp(16)
            rows: 2
            cols: 2
            size_hint_y: 0.1
            Label:
                text: 'Automatic setup using DHCP'
            UseDHCP:
                id: use_dhcp
                active: True
                on_active: root.on_checkbox_active(self, self.state)
""")

runTouchApp(widget)