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# Copyright (c) 2007, Enthought, Inc.
# License: BSD Style.
"""
This demo shows the proper way to create a <b>Property</b> whose value is a
list, especially when the value of the <b>Property</b> will be used in a user
interface, such as with the <b>TableEditor</b>.
Most of the demo is just the machinery to set up the example. The key thing to
note is the declaration of the <i>people</i> trait:
people = Property( List, depends_on = 'ticker' )
In this case, by defining the <b>Property</b> as having a value of type
<b>List</b>, you are ensuring that the computed value of the property will be
validated using the <b>List</b> type, which in addition to verifying that the
value is indeed a list, also guarantees that it will be converted to a
<b>TraitListObject</b>, which is necessary for correct interaction with various
Traits UI editors in a user interface.
Note also the use of the <i>depends_on</i> metadata to trigger a trait property
change whenever the <i>ticker</i> trait changes (in this case, it is changed
every three seconds by a background thread).
Finally, the use of the <i>@cached_property</i> decorator simplifies the
implementation of the property by allowing the <b>_get_people</b> <i>getter</i>
method to perform the expensive generation of a new list of people only when
the <i>ticker</i> event fires, not every time it is accessed.
"""
#-- Imports --------------------------------------------------------------------
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 View, Item, TableEditor
from traitsui.table_column \
import ObjectColumn
#-- 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, depends_on = 'ticker' )
# Tiny hack to allow starting the background thread easily:
begin = Int
#-- Traits View Definitions ------------------------------------------------
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
)
),
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 xrange( randint( 10, 20 ) )
]
#-- Default Value Implementations ------------------------------------------
def _begin_default ( self ):
""" Starts the background thread running.
"""
thread = Thread( target = self._timer )
thread.setDaemon( 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()
|
