When attempting to build more complex widgets/fields, access to form data would be helpful

[freyley]

I'm currently working on building more complex fields with multi-html-element widgets, and connecting them to incoming data models in a way that I think isn't doable in the current design of forms. However, there is a place where fields have access to form data, and that's in the BoundField class in forms.py. If I build my own BoundField class, I can easily give my fields access to the data they need when rendering the widget, as the value() method has access to self.form and self.field. Unfortunately, to build my own BoundField class I have to implement a number of functions in the BaseForm class, one of which, _html_output, is long and not something I actually want to maintain a different version of.

So I propose a minor modification: have BaseForm.__init__ set a self._bound_field_class and then use that everywhere, which allows Form class derivatives to set a different BoundField class.

I am attaching a patch which does just that. It is against 1.3.1

[freyley]

Or better, set it as a class variable

[Jannis Leidel]

Accepting in principal since this might be useful if we'd add template based widget rendering.

[andrebrantom]

I just ran into the solution specified here, but with a slightly different use-case, which is to be able to pass the field's label to the widget so that it can render everything at once (Bootstrap 2 has the notion of control-group for which it makes sense to render it in a single go). The final label is frustratingly only available in the BoundField instance, since that's the only place where the Field and it's declared name come together.

So +1 on this!

[Tim Graham]

The proposed patch is simple enough, but if there are I'm wondering if it would be better to make this a public API with docs and tests?

[Tim Graham]

Duplicate of #25294 which has a more thorough patch.