Question

I’m trying to learn how to use Traits for building simple UIs for my Python scripts. I want to make a programme with a list which the user can add words to with one button, or to clear the list completely with another.

So far, I’ve used traits:

myList = List(Str)

myList = ['Item1','Item2'] #Initial items in list

To display this list in a traits UI, I used ListStrEditor from the traits UI package:

Item('myList', show_label = False, label = 'Data Files', editor = ListStrEditor(auto_add = False)

I have coded 2 buttons:
1) one for ADDing an item to the list (myList.append('item3'))
2) a CLEAR button to empty the list (myList = []). The basic UI is good, the buttons work and my list variable is changed as expected.

However, the problem is, that my list in the GUI doesn’t update. If I click on it the new values are displayed, however. Also, I want to potentially add many items to it and wonder if there is a way to add a scrollbar to the side?

I’ve looked up the ListStrEditor manual and usage, although I’m getting a bit bogged down with terminology. Apparently a refresh() function exists, but I’m not sure how to apply it to ListStrEditor. Also, I’m not sure if I need to use things called “adapters” or “handlers”.

Any tips or pointers in the right direction would be much appreciated!

Answer 1

Without seeing more complete code, it is difficult to know why your code is not working. Perhaps you are missing the use of self? E.g. self.myList.append('Item3') instead of just myList.append('Item3')?

The following works for me. The display of the list updates as soon as the buttons are pressed.

import random

from traits.api import HasTraits, List, Str, Button
from traitsui.api import ListStrEditor, View, UItem


class Demo(HasTraits):

    my_list = List(Str)

    add = Button("ADD")
    clear = Button("CLEAR")

    traits_view = \
        View(
            UItem('my_list', editor=ListStrEditor(auto_add=False)),
            UItem('add'),
            UItem('clear'),
        )

    def _my_list_default(self):
        return ['Item1', 'Item2']

    def _add_fired(self):
        new_item = "Item%d" % random.randint(3, 999)
        self.my_list.append(new_item)

    def _clear_fired(self):
        self.my_list = []


if __name__ == "__main__":
    demo = Demo()
    demo.configure_traits()

It works with both the wx and qt4+pyside backends. I’m using the Enthought python distribution, EPD 7.3, which has version 4.2.0 of Traits and TraitsUI.

If your code is significantly different, could you add it to the question?