A slightly less toy example

Most applications require a little more than a button on a page. Lets build a slightly more complex example - a Fahrenheit to Celcius converter:

Here’s the source code:

from __future__ import print_function, unicode_literals, absolute_import

import toga

def build(app):
    container = toga.Container()

    c_input = toga.TextInput(readonly=True)
    f_input = toga.TextInput()

    c_label = toga.Label('Celcius', alignment=toga.LEFT_ALIGNED)
    f_label = toga.Label('Fahrenheit', alignment=toga.LEFT_ALIGNED)
    join_label = toga.Label('is equivalent to', alignment=toga.RIGHT_ALIGNED)

    def calculate(widget):
        try:
            c_input.value = (float(f_input.value)- 32.0) * 5.0 / 9.0
        except:
            c_input.value = '???'

    button = toga.Button('Calculate', on_press=calculate)

    container.add(c_input)
    container.add(f_input)

    container.add(c_label)
    container.add(f_label)
    container.add(join_label)

    container.add(button)

    container.constrain(f_input.WIDTH == 100)
    container.constrain(f_input.TRAILING + 20 == f_label.LEADING)
    container.constrain(f_label.TRAILING + 20 == container.TRAILING)
    container.constrain(f_input.TOP == container.TOP + 20)
    container.constrain(f_input.TOP == f_label.TOP)

    container.constrain(c_input.WIDTH == f_input.WIDTH)
    container.constrain(c_label.WIDTH == f_label.WIDTH)
    container.constrain(c_input.TRAILING + 20 == c_label.LEADING)
    container.constrain(c_label.TRAILING + 20 == container.TRAILING)
    container.constrain(c_input.TOP == f_input.BOTTOM + 20)
    container.constrain(c_input.TOP == c_label.TOP)

    container.constrain(c_input.LEADING == f_input.LEADING)
    container.constrain(join_label.TOP == c_label.TOP)
    container.constrain(join_label.LEADING == container.LEADING + 20)
    container.constrain(join_label.TRAILING + 20 == c_input.LEADING)

    container.constrain(button.TOP == c_input.BOTTOM + 20)
    container.constrain(button.LEADING == c_input.LEADING)
    container.constrain(button.TRAILING == c_label.TRAILING)
    container.constrain(button.BOTTOM + 20 == container.BOTTOM)

    return container


if __name__ == '__main__':
    app = toga.App('Temperature Converter', 'org.pybee.f_to_c', startup=build)

    app.main_loop()