Custom widgets in zope.formlib

zope.formlib has the ability to customize the used widget like this:

class KeywordsManagementForm(five.formlib.formbase.SubPageForm):
    form_fields = zope.formlib.form.Fields(IKeywords)
    form_fields['keywords'].custom_widget = KWSelectWidgetFactory

I do not like this approach for two reasons:

  • the widget has to be set manually¬†every time the specific field is used
  • there is no easy way to get a display widget if the form or field is not editable for the user

Defining a new schema field and registering the widget for this field seems a bit heavy, so I came up with providing a marker interface on the field:

class IHaveSelectableKeywords(zope.interface.Interface):
    """Marker interface to get a special keywords widget."""

class IKeywords(zope.interface.Interface):
    keywords = zope.schema.List(
        title = _("Edit Keywords"),
        value_type = zope.schema.Choice(
            vocabulary=u"uc.keywords.Keywords"))
    zope.interface.alsoProvides(keywords, IHaveSelectableKeywords)

I registered the edit widget and display widget for the IHaveSelectableKeywords interface, so the custom widget does not have to be set in the form like this (edit widget):

<adapter
   for=".IHaveSelectableKeywords
        zope.publisher.interfaces.browser.IBrowserRequest"
 provides="zope.app.form.browser.interfaces.ISimpleInputWidget"
 factory=".KWSelectWidgetFactory"
 permission="zope.Public" />