基类视图

A view is a callable which takes a request and returns a response. This can be more than just a function, and Django provides an example of some classes which can be used as views. These allow you to structure your views and reuse code by harnessing inheritance and mixins. There are also some generic views for simple tasks which we’ll get to later, but you may want to design your own structure of reusable views which suits your use case. For full details, see the class-based views reference documentation.

Basic examples

Django provides base view classes which will suit a wide range of applications. All views inherit from the View class, which handles linking the view in to the URLs, HTTP method dispatching and other simple features. RedirectView is for a simple HTTP redirect, and TemplateView extends the base class to make it also render a template.

Simple usage in your URLconf

The simplest way to use generic views is to create them directly in your URLconf. If you’re only changing a few simple attributes on a class-based view, you can simply pass them into the as_view() method call itself:

from django.conf.urls import patterns
from django.views.generic import TemplateView

urlpatterns = patterns('',
    (r'^about/', TemplateView.as_view(template_name="about.html")),
)

Any arguments passed to as_view() will override attributes set on the class. In this example, we set template_name on the TemplateView. A similar overriding pattern can be used for the url attribute on RedirectView.

Subclassing generic views

The second, more powerful way to use generic views is to inherit from an existing view and override attributes (such as the template_name) or methods (such as get_context_data) in your subclass to provide new values or methods. Consider, for example, a view that just displays one template, about.html. Django has a generic view to do this - TemplateView - so we can just subclass it, and override the template name:

# some_app/views.py
from django.views.generic import TemplateView

class AboutView(TemplateView):
    template_name = "about.html"

Then we just need to add this new view into our URLconf. ~django.views.generic.base.TemplateView is a class, not a function, so we point the URL to the as_view() class method instead, which provides a function-like entry to class-based views:

# urls.py
from django.conf.urls import patterns
from some_app.views import AboutView

urlpatterns = patterns('',
    (r'^about/', AboutView.as_view()),
)

For more information on how to use the built in generic views, consult the next topic on generic class based views.

Supporting other HTTP methods

Suppose somebody wants to access our book library over HTTP using the views as an API. The API client would connect every now and then and download book data for the books published since last visit. But if no new books appeared since then, it is a waste of CPU time and bandwidth to fetch the books from the database, render a full response and send it to the client. It might be preferable to ask the API when the most recent book was published.

We map the URL to book list view in the URLconf:

from django.conf.urls import patterns
from books.views import BookListView

urlpatterns = patterns('',
    (r'^books/$', BookListView.as_view()),
)

And the view:

from django.http import HttpResponse
from django.views.generic import ListView
from books.models import Book

class BookListView(ListView):
    model = Book

    def head(self, *args, **kwargs):
        last_book = self.get_queryset().latest('publication_date')
        response = HttpResponse('')
        # RFC 1123 date format
        response['Last-Modified'] = last_book.publication_date.strftime('%a, %d %b %Y %H:%M:%S GMT')
        return response

If the view is accessed from a GET request, a plain-and-simple object list is returned in the response (using book_list.html template). But if the client issues a HEAD request, the response has an empty body and the Last-Modified header indicates when the most recent book was published. Based on this information, the client may or may not download the full object list.

Decorating class-based views

Since class-based views aren’t functions, decorating them works differently depending on if you’re using as_view or creating a subclass.

Decorating in URLconf

The simplest way of decorating class-based views is to decorate the result of the as_view() method. The easiest place to do this is in the URLconf where you deploy your view:

from django.contrib.auth.decorators import login_required, permission_required
from django.views.generic import TemplateView

from .views import VoteView

urlpatterns = patterns('',
    (r'^about/', login_required(TemplateView.as_view(template_name="secret.html"))),
    (r'^vote/', permission_required('polls.can_vote')(VoteView.as_view())),
)

This approach applies the decorator on a per-instance basis. If you want every instance of a view to be decorated, you need to take a different approach.

Decorating the class

To decorate every instance of a class-based view, you need to decorate the class definition itself. To do this you apply the decorator to the dispatch() method of the class.

A method on a class isn’t quite the same as a standalone function, so you can’t just apply a function decorator to the method – you need to transform it into a method decorator first. The method_decorator decorator transforms a function decorator into a method decorator so that it can be used on an instance method. For example:

from django.contrib.auth.decorators import login_required
from django.utils.decorators import method_decorator
from django.views.generic import TemplateView

class ProtectedView(TemplateView):
    template_name = 'secret.html'

    @method_decorator(login_required)
    def dispatch(self, *args, **kwargs):
        return super(ProtectedView, self).dispatch(*args, **kwargs)

In this example, every instance of ProtectedView will have login protection.

注解

method_decorator passes *args and **kwargs as parameters to the decorated method on the class. If your method does not accept a compatible set of parameters it will raise a TypeError exception.