TextInput.on_change does not seem to work

Hello! I just started learning toga and played with tutorial “A slightly less toy example” and came across a problem. Please tell me, it’s a bug or I’m doing something wrong.

Expected Behavior

I added on_change handler to f_input: f_input.on_change = calculate. I expect that when you change the value in the field, the function calculate will be called.

Current Behavior

The function calculate is not called.

Your Environment

• Python Version (list the specific version number) 3.5

• Operating System and Version (select from the following and list the specific version number; if your OS is not listed, list that as well)

  • macOS - version:
  • Linux - distro: Mint - version: 18.3
  • Windows - version:
  • Other - name: - version:

• Toga Target (the type of app you are trying to generate)

  • android
  • cocoa
  • django
  • gtk
  • iOS
  • tvOS
  • watchOS
  • winforms
  • win32
  • Other (please specify)

[freakboy3742]

I think the credit for the full fix goes to @cachitas in acc206d; but I agree this is now fixed.

[DariusMontez]

It looks like @maranas resolved this issue back in Mar 2019 here by subscribing to the changed event of the native Gtk widget. From GTK Reference - the "changed" signal

I installed toga-0.3.0.dev20 this morning and am not experiencing this issue. My on_change handler is being fired on every keystroke or after a cut or a paste. Using this app with only a text input: (can be pasted directly into console)

import toga
def build(app):
    return toga.TextInput(on_change=print)

toga.App('app', 'app', startup=build).main_loop()