Kivy, dynimic class on KV language

Question

I'm trying to use a rule on my KV language to generate classes on the on, but I always get an error.

<SimpleInputLayout>:
    orientation: 'vertical'

    message_label: message
    user_input: input

    Label:
        id: message
        text: root.message_to_user
    FloatInput: if input_type == 'float' else TextInput:
        id: input
        focus: True

What can I do to make this works, if input_type is equal 'float' I want my input class to be a FloatInput , else a TextInput .

Answer 1

Such thing isn't possible with kv lang alone. At least not directly. You have ~4 options:

1. Set input_type according to a property of a widget:

    TextInput: hint_text: 'int' input_type: 'int' if self.hint_text == 'int' else 'float' 

2. Change input.input_type property from outside (if the difference is only input type)

3. Add the right widget dynamically with eg <parent>.add_widget(Factory.FloatInput()) on some event, let's say on_release of a Button
4. Do it in Python especially in __init__ when building the layout. It's easier than messing around trying to implement something that's not there or looking for the right event to use for adding a widget in kv . It's more flexible.

Although there's probably mentioned in the docs the thing that everything after : behaves like a casual Python, but that applies to widget properties & events, not to widgets themselves:

bad:

v--rule-- :  v------------ not Python -------------v
FloatInput: if input_type == 'float' else TextInput:

good:

TextInput:
    text: 'int'
    # property:  v-------------- Python ---------------v
    input_type: 'int' if self.text == 'int' else 'float'