Custom Django CheckboxSelectMultiple widget rendered as an empty list

Question

I am trying to create a CheckboxSelectMultiple widget that lists all the content types of my project. I started by using the base widget when defining a MultipleChoiceField field in a ModelForm and it worked fine. I would like now to make it a custom widget I can import though an app into any project.

Here is the code I am using:

# myapp/models.py

from django.db import models

class Tiger(models.Model):
    color = models.CharField(max_length=100)

# myapp/admin.py

from django import forms
from django.contrib import admin
from django.contrib.contenttypes.models import ContentType
from myapp.models import Tiger

class TigerForm(forms.ModelForm):
    """
    Default ModelForm that will be overriden.
    """
    class Meta:
        model = Tiger

This is where I define my custom widget. I am guessing I am not passing the list of values correctly (see comment in the code).

class TigerWidget(forms.CheckboxSelectMultiple):
    """
    Custom widget that displays a list of checkboxes for each content type.
    The goal is to make it generic enough to put it in an external app
    that can be imported into any project.
    """
    def __init__(self, attrs=None, choices=()):

        # List all content types
        content_types = ContentType.objects.all()
        classes = tuple([(c.model, c.name) for c in content_types])

        # Define widget choices as the list of these content types
        self.choices = classes  # I am guessing it should be done differently?

        # Select all of them by default
        self.initial = [c[0] for c in classes]

        # Same behavior as parent
        super(TigerWidget, self).__init__(attrs)

Here are the remaining classes that make use of it.

class TigerCustomForm(TigerForm):
    """
    Custom form that adds a field using the custom widget to the form.
    """
    # content_types = ContentType.objects.all()
    # classes = tuple([(c.model, c.name) for c in content_types])

    # This works fine.
    # nickname = forms.MultipleChoiceField(
    #     widget=forms.CheckboxSelectMultiple,
    #     choices=classes,
    #     # Select all by default
    #     initial=[c[0] for c in classes]
    # )

    # This does not. An empty list (<ul></ul>) is rendered in the place of the widget.
    nickname = forms.MultipleChoiceField(
        widget=TigerWidget,
    )

class TigerAdmin(admin.ModelAdmin):
    form = TigerCustomForm

admin.site.register(Tiger, TigerAdmin)
admin.site.register(ContentType)

Thanks in advance for your help.

Answer 1

A widget is responsible for rendering the html e.g. display a multiple select box (forms.MultipleSelect) or multiple checkboxes (forms.CheckboxSelectMultiple). This is a separate decision from the choices to display for the field.

I think it would be better to subclass forms.MultipleChoiceField and set the choices there.

class TigerMultipleChoiceField(forms.MultipleChoiceField):
    """
    Custom widget that displays a list of checkboxes for each content type.
    The goal is to make it generic enough to put it in an external app
    that can be imported into any project.
    """
    def __init__(self, *args, **kwargs):
        # Same behavior as parent
        super(TigerMultipleChoiceField, self).__init__(*args, **kwargs)


        # List all content types
        content_types = ContentType.objects.all()
        classes = tuple([(c.model, c.name) for c in content_types])

        # Define widget choices as the list of these content types
        self.choices = classes

        # Select all of them by default
        self.initial = [c[0] for c in classes]

Answer 2

I managed to find a workaround by passing the choices to the custom widget through the custom field. The initial parameter being inherited from the Field class, I defined it in the custom Field constructor method.

Here the final code:

class TigerWidget(forms.CheckboxSelectMultiple):
    """
    Custom widget that displays a list of checkboxes for
    each content type.
    The goal is to make it generic enough to put it  in an
    external app that can be imported into any project.
    """
    def __init__(self, attrs=None, choices=()):
        super(TigerWidget, self).__init__(attrs=attrs, choices=choices)

class TigerField(forms.Field):
    """
    Custom Field that makes use of the custom widget (in the external app too). It will need to be herited
    from.
    """
    # Default behavior: displays all existing content types. Can be overriden in
    # the child class.
    content_types = ContentType.objects.all()
    choices = tuple([(c.model, c.name) for c in content_types])

    widget = TigerWidget(choices=choices)

    def __init__(self, *args, **kwargs):
        super(TigerField, self).__init__(args, kwargs)
        # Selects all by default
        self.initial = [c[0] for c in self.__class__.choices]