Question

在通用视图中的基类中，django在运行时创建方法view，将其附加到通用视图类，然后在该类上调用dispatch方法

我不明白这种方法的目的，为什么没有直接从as_view方法调用dispatch方法？

class View(object):
    """
    Intentionally simple parent class for all views. Only implements
    dispatch-by-method and simple sanity checking.
    """

    http_method_names = ['get', 'post', 'put', 'delete', 'head', 'options', 'trace']

    def __init__(self, **kwargs):
        """
        Constructor. Called in the URLconf; can contain helpful extra
        keyword arguments, and other things.
        """
        # Go through keyword arguments, and either save their values to our
        # instance, or raise an error.
        for key, value in kwargs.iteritems():
            setattr(self, key, value)

    @classonlymethod
    def as_view(cls, **initkwargs):
        """
        Main entry point for a request-response process.
        """
        # sanitize keyword arguments
        for key in initkwargs:
            if key in cls.http_method_names:
                raise TypeError(u"You tried to pass in the %s method name as a "
                                u"keyword argument to %s(). Don't do that."
                                % (key, cls.__name__))
            if not hasattr(cls, key):
                raise TypeError(u"%s() received an invalid keyword %r" % (
                    cls.__name__, key))

        def view(request, *args, **kwargs):
            self = cls(**initkwargs)
            return self.dispatch(request, *args, **kwargs)

        # take name and docstring from class
        update_wrapper(view, cls, updated=())

        # and possible attributes set by decorators
        # like csrf_exempt from dispatch
        update_wrapper(view, cls.dispatch, assigned=())
        return view

    def dispatch(self, request, *args, **kwargs):
        # Try to dispatch to the right method; if a method doesn't exist,
        # defer to the error handler. Also defer to the error handler if the
        # request method isn't on the approved list.
        if request.method.lower() in self.http_method_names:
            handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
        else:
            handler = self.http_method_not_allowed
        self.request = request
        self.args = args
        self.kwargs = kwargs
        return handler(request, *args, **kwargs)

    def http_method_not_allowed(self, request, *args, **kwargs):
        allowed_methods = [m for m in self.http_method_names if hasattr(self, m)]
        logger.warning('Method Not Allowed (%s): %s' % (request.method, request.path),
            extra={
                'status_code': 405,
                'request': self.request
            }
        )
        return http.HttpResponseNotAllowed(allowed_methods)

Answer 1

在基于类的通用视图中，任何请求都应该拥有自己的MyView类实例。

这是我们的urls.py：

from foo.views import AboutView
....
(r'^about/', AboutView.as_view()),

每个django线程导入

urls.py一次。这意味着调用as_view不会创建AboutView的实例。

当urlconf处理请求时，将调用view()方法，然后只创建AboutView实例，并传递并填充此特定请求所需的所有相关数据。

使用：

(r'^about/', AboutView().dispatch), #WRONG!!!!

将导致所有请求共享同一个视图实例，包括不应被不同请求重用的可能属性。

为什么在这堂课中采用这种方法？

1 个答案: