Initializing a list view on startup

[Al Dante]

Hi, 

I have very little experience with Kivy and my apologies if this is a newbie question. 

I am writing a Cocktails app, using Screens to guide users in their choices. E.g the first screen has buttons allowing the user to select following screens containing gin cocktails, rum cocktails, or to pick by flavour or type. 

If the user selects Gin cocktails, the next screen shows a single-selectable list of gin cocktails.  

How do I populate this list on entry to the screen?

The original uses a button, which when pressed, fills the list entries. As my list is static, I would like to avoid this. All the methods I have tried fail because the widget data property is not initialized at that point and is set to "None". 

I am using the SelectableLabel / SelectableBoxLayout / AddLocationForm from here: Kivy: Unknown class <ListView> error code but updated for Kivy 2.0. 

Many thanks in advance for your help.

[Elliot Garbus]

Screens have events that you can use.

I suggest you use on_pre_enter:

This will fire prior the animation of the screen transition.

https://kivy.org/doc/stable-1.11.1/api-kivy.uix.screenmanager.html?highlight=screenmanager#kivy.uix.screenmanager.Screen

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[victo...@googlemail.com]

Thank you very much - I will try that.

[victo...@googlemail.com]

Thank you - that works perfectly.

[victo...@googlemail.com]

class CocktailsList(BoxLayout):
    selectable_cocktails = ObjectProperty()

class CocktailsScreen(Screen):
    cocktails_list = ObjectProperty()

    def on_pre_enter(self, *args):

    print("Screen pre-enter")
    self.populate()

    form = None
    for child in self.children:
        if 'selectable_cocktails_list' in child.ids:

            # Copy cocktails into List widget
            child.selectable_cocktails.data = [{'text': x['name.text']} for x in self.cocktails_list]
            break
--------------------------- kv
<CocktailsScreen>:
    name: "cocktails"
    CocktailsList:

<SelectableLabel>:
    # Draw a background to indicate selection
    canvas.before:
        Color:
        rgba: (1, 0, 0, 1) if self.selected else (.0, 0.9, .1, .3)

    Rectangle:
        pos: self.pos

        size: self.size

    Color:
        rgba: (.0, 0.9, .1, .3)

    Rectangle:
        pos: self.pos

        size: self.size

<CocktailsList>:
    orientation: "vertical"
    id: fred

    # The label (selectable_cocktails) must match the variable defined in the AddLocationForm class
    # The value (selectable_cocktails_list) must match the id of the RecycleView defined below
    selectable_cocktails: selectable_cocktails_list

    RecycleView:
        id: selectable_cocktails_list

        name: "rvcocktailslist"

        viewclass: 'SelectableLabel'

        SelectableRecycleBoxLayout:

            default_size: None, dp(26)

            default_size_hint: 1, None

            size_hint_y: None

            height: self.minimum_height

            orientation: 'vertical'

            multiselect: False

            touch_multiselect: False