RecycleView: Add behavior to set RV data using kv ids

[matham]

Adds the RecycleKVIDsDataViewBehavior class. Fixes #6878.

It's similar to the existing RecycleDataViewBehavior class, except that the data can signify properties of objects named with an id in KV. E.g. given a KV rule::

<MyRule@RecycleKVIDsDataViewBehavior+BoxLayout>:
    Label:
        id: name
    Label:
        id: value

Then setting the data list with rv.data = [{'name.text': 'Kivy user', 'value.text': '12'}] would automatically set the corresponding labels.

[tshirtman]

looks fine, though i think maybe it can be improved, see comment.

[tshirtman]

why the star? the maxsplit makes it a 2-tuple, so we should be able to directly use the value without indexing on the next line.

Also, i think like ids is not a great name here, as name actually refer to a kv id, and ids here would be a chain of one or more attributes.
And why the maxsplit actually? Do we really want to set an attribute with dots in it? wouldn't it be better to iterate on the names, getting the next value until the penultimate one and use setattr on this one?

wid, *attrs = key.split('.')
obj = self
for attr in attrs[:-1]:
    obj = getattr(obj, attr)
setattr(obj, attrs[-1], value)

or would that cause issues i can't think of right now?

[matham]

why the star? the maxsplit makes it a 2-tuple, so we should be able to directly use the value without indexing on the next line.

Because the maxsplit is 1 we can have at most 2 items. But it could also be only 1. In the latter case, ids will be empty.

[matham]

Also, i think like ids is not a great name here, as name actually refer to a kv id, and ids here would be a chain of one or more attributes.

I feel like that's nitpicking because in the normal case it is the property name, except when it's interpreted as an id :) But also, I think you may have misunderstood what this is doing. Specifically, with the following KV examples:

MyRule:
    street: ''
    Label:
        id: address

<RootRule@RecycleKVIDsDataViewBehavior>:
    country: ''
    Label:
        id: phone
    MyRule:
        id: my_rule

Setting data to [{'country': 'US', 'phone.text': '123456', 'my_rule.street': 'Home ave', 'my_rule.address.text': '555'}]. Under the current code, my_rule will have a attribute named address.text created and set to 555. That's because we don't recursively go through rules like your example code. We only allow accessing the ids at the first level. Hence the only 1 split by period. Under your code, it would set the text property of the address widget to 555.

The reason is that I don't think it would be common in kivy to set properties this way for sub rules and sub-sub rules etc. So I don't think we should complicate the API by adding this. Because once we add that it's hard to remove such functionality and I'd prefer to wait until this specifically is requested. And even then I think we can just add such recursive ids access a doc recipe. For now, this API only allows setting the property of a widget named in the root rule of the class.

[tshirtman]

ok, i did think a recursive definition could be useful, but i agree it might be a strong commitment that we might not need to make.

Under the current code, my_rule will have a attribute named address.text created and set to 555

I think that's what i meant with "Do we really want to set an attribute with dots in it?", that seems like a weird requirement to me, and i think i'd rather produce an error, saying that recursive setting (what i would expect by putting dots in the key) is not supported, than create attributes with dots in them, that can only be accessed through getattr, and won't properly bind in kvlang.

[matham]

I suppose we can raise an exception if there is more than one dot, in case users think that it does work recursively.

[matham]

Ok, I added that.

[tshirtman]

i feel the exception message could be improved, i'm not sure i would immediately understand why it's a problem, but reading the doc of the class should help, and it's a cool feature.

[matham]

Yeah, I agree the message can be improved. But I couldn't think of a way to state it without writing a essay so I figured explaining it in the docs will have to be sufficient :)

[chavarinbonbyn]

Which kivy version will contain this change ?

[tshirtman]

next RC or release of 2.0.