# Django 2.2.9.dev20191202104323 文档

# The form rendering API

Django's form widgets are rendered using Django's template engines system.

The form rendering process can be customized at several levels:

- Widgets can specify custom template names.
- Forms and widgets can specify custom renderer classes.
- A widget's template can be overridden by a project. (Reusable applications typically shouldn't override built-in templates because they might conflict with a project's custom templates.)

## The low-level render API

The rendering of form templates is controlled by a customizable renderer class. A custom renderer can be specified by updating the `FORM_RENDERER` setting. It defaults to `'``django.forms.renderers.DjangoTemplates``'`.

You can also provide a custom renderer by setting the `Form.default_renderer` attribute or by using the `renderer` argument of `Widget.render()`.

Use one of the built-in template form renderers or implement your own. Custom renderers must implement a `render(template_name, context, request=None)` method. It should return a rendered templates (as a string) or raise `TemplateDoesNotExist`.

## Built-in-template form renderers

### `DjangoTemplates`

class `DjangoTemplates`

This renderer uses a standalone `DjangoTemplates` engine (unconnected to what you might have configured in the `TEMPLATES` setting). It loads templates first from the built-in form templates directory in `django/forms/templates` and then from the installed apps' templates directories using the `app_directories` loader.

If you want to render templates with customizations from your `TEMPLATES` setting, such as context processors for example, use the `TemplatesSetting` renderer.

### `Jinja2`

class `Jinja2`

This renderer is the same as the `DjangoTemplates` renderer except that it uses a `Jinja2` backend. Templates for the built-in widgets are located in `django/forms/jinja2` and installed apps can provide templates in a `jinja2` directory.

To use this backend, all the widgets in your project and its third-party apps must have Jinja2 templates. Unless you provide your own Jinja2 templates for widgets that don't have any, you can't use this renderer. For example, `django.contrib.admin` doesn't include Jinja2 templates for its widgets due to their usage of Django template tags.

### `TemplatesSetting`

class `TemplatesSetting`

This renderer gives you complete control of how widget templates are sourced. It uses `get_template()` to find widget templates based on what's configured in the `TEMPLATES` setting.

Using this renderer along with the built-in widget templates requires either:

- `'django.forms'` in `INSTALLED_APPS` and at least one engine with `APP_DIRS=True`.

- Adding the built-in widgets templates directory in `DIRS` of one of your template engines. To generate that path:

      import django
      django.__path__[0] + '/forms/templates'  # or '/forms/jinja2'

Using this renderer requires you to make sure the form templates your project needs can be located.

## Context available in widget templates

Widget templates receive a context from `Widget.get_context()`. By default, widgets receive a single value in the context, `widget`. This is a dictionary that contains values like:

- `name`
- `value`
- `attrs`
- `is_hidden`
- `template_name`

Some widgets add further information to the context. For instance, all widgets that subclass `Input` defines `widget['type']` and `MultiWidget` defines `widget['subwidgets']` for looping purposes.

## Overriding built-in widget templates

Each widget has a `template_name` attribute with a value such as `input.html`. Built-in widget templates are stored in the `django/forms/widgets` path. You can provide a custom template for `input.html` by defining `django/forms/widgets/input.html`, for example. See Built-in widgets for the name of each widget's template.

To override widget templates, you must use the `TemplatesSetting` renderer. Then overriding widget templates works the same as overriding any other template in your project.