When does self.ids get filled...

[Paul]

I'm reasonably new to Kivy, but donkey's years as a dev.

I like the concept of kv files (not polluting logic with UI layout) - 

so I've laid out my complete app inside the kv file.

The classes behind the major UI elements are in my main.py.

My issue is that:

- I call 

    theApp.run(),

- In the App build method, I construct my MainWindow().

    class PrivateApp(App):

    def build(self):
        self.main = MainWindow()
        print("self.main.ids", self.main.ids)
        return self.main

This all works. The app is constructed, all the UI elements are constructed and work.

The problem is that in one corner of the UI I have a ListView (notelist_items below)

And in there I have an adapter. I declare the adapter in kv:

<NotesListContainer>:
    notelist_header: notelist_header
    notelist_items: notelist_items
    orientation: 'vertical'

    ...

    ListView:
        id: notelist_items
        orientation: 'vertical'
        adapter: main.NotesListAdapter(data=root.data, cls=Factory.NoteListItem, args_converter=root.args_converter, allow_empty_selection=False, selection_mode='single', on_selection_change=root.sel_change, propagate_selection_to_data=True)

I have learnt out that you cannot declare the on_selection_change in the kv file - it must be done in code. 
So I do that...

class NotesListContainer(BoxLayout):
    data = ListProperty()
    notelist_items = ObjectProperty()
    note_contents = None

    def __init__(self, **kwargs):
        super(NotesListContainer, self).__init__(**kwargs)

        print("IDS", self.ids)
        self.ids["notelist_items"].adapter.bind(on_selection_change=self.sel_change)


I have seen example code where you *can* access self.ids in the constructor.
(e.g. see the accepted answer in here: http://stackoverflow.com/questions/24297061/kivy-binding-a-callback-to-simplelistadapter-in-kv)
Which is what I am doing here. But self.ids is *empty* at this point (as the print proved).

You'll notice above that I print ids at the end of the app.build(), and it is full at that point.
But ids is empty end of the NotesListContainer constructor.

It seems I need to bind on_selection_change to my adapters after build, right?
If so, is there a widget event that fires after build is complete?

Or have I got this wrong?
Thx for any advice you can give.

Paul.

[David Aldrich]

Hi Paul

I faced a similar problem and was advised to:

Do Clock.schedule_once(some_func, 0), where some_func does your thing with the ids

I called that from init() and it worked ok.

Best regards

David

[Paul]

That did it! Thank you.

I made some pretty ugly calls from the MainWindow constructor to go back and complete construction

when the ids are all set. Doing a scheduled call

using a lambda right from the class where its required is much better.

    Clock.schedule_once(lambda dt: self.notelist_items.adapter.bind(on_selection_change=self.sel_change), 0)

Still a little ugly IMHO, but workable.

Cheers

Paul

[ZenCODE]

Another option is to use the event to do the binding, not the init. Something like:

def on_notelist_items(self, widget, value):
    self.notelist_items.adapter.bind(on_selection_change=self.sel_change)   

[Paul]

Interesting. I think you are suggesting that I create a custom event, and then send

that event to all objects that need post-init setup, right?

That's a pretty cool idea, although I would need a way to keep a list of objects

that require that post-initialiser setup.

Thank you.

Paul.

[ZenCODE]

Not sure I'd word it like that. It's more like, instead of using your __init__ to bind, you use the event of the 'nodelist_items' property changing to do the binding. It's fired when your 'nodelist_items' property changes to something other than None.

It's not really a custom event as this is an automatic event provided by Kivy properties. So I'm not sure why you would need to keep a list? But then again I have not looked closely at what you are trying to do. Just wanted point out you can use these events for initialization i.s.o. __init__. It avoids that issue of the ids not being set up yet..:-)

[Paul]

Got it - I had forgotten about that. Event on changing the nodelist_items value.

Will the adapter necessarily have a value at that point?

Thanks.

Paul.

[ZenCODE]

Not sure. Try it and see? You can guard against that error but then the question remains on where to set it...

def on_notelist_items(self, widget, value):
    if self.notelist_items.adapter:
        self.notelist_items.adapter.bind(on_selection_change=self.sel_change)
    else:
        print('Eek! This is not going to work!')

 

[Paul]

Yep. That did it.

I changed it to:

def on_notelist_items(self, widget, value):

    if self.notelist_items.adapter:

        print('Adapter set')

        self.notelist_items.adapter.bind(on_selection_change=self.sel_change)

    else:

        print('Eek! This is not going to work!')

    print("IDS: ", self.ids)

because I also wanted to see if the ids dict had been filled in at the time this event fires.

And it has!!! On the output appeared the following:

Adapter set

('IDS: ', {'notelist_header': <WeakProxy to <kivy.uix.boxlayout.BoxLayout object at 0x114d63db8>>, 'notelist_items': <WeakProxy to <kivy.uix.listview.ListView object at 0x114d9d7a0>>})

Thanks for the help.

Paul.