Add media descriptions to newforms widgets

[Russell Keith-Magee]

A newforms widget currently defines the way to render a user interface input element. However, in order to make interesting input elements, you also need other media - i.e., Javascript and CSS. These requirements can be defined on a per-widget basis (a Date field requires a Calendar widget; the calendar widget requires media/calendar.js and media/calendar.css).

At present, there is no easy way to:

1. identify what media is required to display a form
2. identify and eliminate any duplicate media requirements, e.g., a base css file required by two different widgets on a form.

newforms-admin has some hand rolled functionality to determine Javascript requirements for a page. This ticket describes a more general solution that could be applied to any widget, and therefore to any form.

It involves adding a meta-class to Widget that processes a 'Media' inner class; this inner class is turned into a 'Media' object. Media objects can be printed (yielding <link> and <script> statements). Media objects can also be added, so media from one widget can be added to another widget, yielding the union of required media.

Forms are also modified; you can interrogate form.media to find out the union of all CSS and JavaScript required by a given form.

Discussed in detail here:
​http://groups.google.com/group/django-developers/browse_thread/thread/58fc9cab819c08b9/af54bb9c638fede7#af54bb9c638fede7

[Russell Keith-Magee]

Adds a Media descriptor to newforms widgets

[Russell Keith-Magee]

Revised media patch, to address inheritance issues.

[Russell Keith-Magee]

Media descriptors for newforms, v3; against [5636]

[Russell Keith-Magee]

Media descriptors for newforms-admin; against [5636]

[Russell Keith-Magee]

Improved media descriptors for newforms-admin; against [5651]

[Russell Keith-Magee]

(In [5926]) newforms-admin: Fixed #4418 -- Added the ability for widgets, forms, and Admin declarations to have media definitions.