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# (C) Copyright 2004-2023 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!
"""
This demo shows the proper way to create a **Property** whose value is a
list, especially when the value of the **Property** will be used in a user
interface, such as with the **TableEditor**.
Most of the demo is just the machinery to set up the example. The key thing to
note is the declaration of the *people* trait:
people = Property( List, observe = 'ticker' )
In this case, by defining the **Property** as having a value of type
**List**, you are ensuring that the computed value of the property will be
validated using the **List** type, which in addition to verifying that the
value is indeed a list, also guarantees that it will be converted to a
**TraitListObject**, which is necessary for correct interaction with various
Traits UI editors in a user interface.
Note also the use of the *observe* metadata to trigger a trait property
change whenever the *ticker* trait changes (in this case, it is changed
every three seconds by a background thread).
Finally, the use of the *@cached_property* decorator simplifies the
implementation of the property by allowing the **_get_people** *getter*
method to perform the expensive generation of a new list of people only when
the *ticker* event fires, not every time it is accessed.
"""
from random import randint, choice
from threading import Thread
from time import sleep
from traits.api import (
HasStrictTraits,
HasPrivateTraits,
Str,
Int,
Enum,
List,
Event,
Property,
cached_property,
)
from traitsui.api import ObjectColumn, Item, TableEditor, View
# -- Person Class ---------------------------------------------------------
class Person(HasStrictTraits):
"""Defines some sample data to display in the TableEditor."""
name = Str()
age = Int()
gender = Enum('Male', 'Female')
# -- PropertyListDemo Class -----------------------------------------------
class PropertyListDemo(HasPrivateTraits):
"""Displays a random list of Person objects in a TableEditor that is
refreshed every 3 seconds by a background thread.
"""
# An event used to trigger a Property value update:
ticker = Event()
# The property being display in the TableEditor:
people = Property(List, observe='ticker')
# Tiny hack to allow starting the background thread easily:
begin = Int()
# -- Traits View Definitions ----------------------------------------------
traits_view = View(
Item(
'people',
show_label=False,
editor=TableEditor(
columns=[
ObjectColumn(name='name', editable=False, width=0.50),
ObjectColumn(name='age', editable=False, width=0.15),
ObjectColumn(name='gender', editable=False, width=0.35),
],
auto_size=False,
show_toolbar=False,
sortable=False,
),
),
title='Property List Demo',
width=0.25,
height=0.33,
resizable=True,
)
# -- Property Implementations ---------------------------------------------
@cached_property
def _get_people(self):
"""Returns the value for the 'people' property."""
return [
Person(
name='%s %s'
% (
choice(['Tom', 'Dick', 'Harry', 'Alice', 'Lia', 'Vibha']),
choice(['Thomas', 'Jones', 'Smith', 'Adams', 'Johnson']),
),
age=randint(21, 75),
gender=choice(['Male', 'Female']),
)
for i in range(randint(10, 20))
]
# -- Default Value Implementations ----------------------------------------
def _begin_default(self):
"""Starts the background thread running."""
thread = Thread(target=self._timer)
thread.daemon = True
thread.start()
return 0
# -- Private Methods ------------------------------------------------------
def _timer(self):
"""Triggers a property update every 3 seconds for 30 seconds."""
for i in range(10):
sleep(3)
self.ticker = True
# Create the demo:
demo = PropertyListDemo()
demo.begin
# Run the demo (if invoked from the command line):
if __name__ == '__main__':
demo.configure_traits()
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