Django View类的解析

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', 'patch', '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 six.iteritems(kwargs):            setattr(self, key, value)    @classonlymethod    def as_view(cls, **initkwargs):        """        Main entry point for a request-response process.        """        for key in initkwargs:            if key in cls.http_method_names:                raise TypeError("You tried to pass in the %s method name as a "                                "keyword argument to %s(). Don't do that."                                % (key, cls.__name__))            if not hasattr(cls, key):                raise TypeError("%s() received an invalid keyword %r. as_view "                                "only accepts arguments that are already "                                "attributes of the class." % (cls.__name__, key))        def view(request, *args, **kwargs):            self = cls(**initkwargs)            if hasattr(self, 'get') and not hasattr(self, 'head'):                self.head = self.get            self.request = request            self.args = args            self.kwargs = kwargs            return self.dispatch(request, *args, **kwargs)        view.view_class = cls        view.view_initkwargs = initkwargs        # 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        return handler(request, *args, **kwargs)    def http_method_not_allowed(self, request, *args, **kwargs):        logger.warning(            'Method Not Allowed (%s): %s', request.method, request.path,            extra={'status_code': 405, 'request': request}        )        return http.HttpResponseNotAllowed(self._allowed_methods())

View类的部分源码如上所示。那么平时使用 类 类型的视图是如何解析的呢，下面进行简单介绍：

在url中通常有如下代码

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urlpatterns=[

    url(r'^$',SomeView.as_view(),name='index'),

    url(r'^about/$',AboutView.as_view(),name='about'),

]

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当有人访问我们的网站根目录的时候，url会在url列表中进行匹配，找到第一个匹配项则把对应的request和其他参数传递给对应的视图

那么在上面的urlpatterns中则一定会匹配到第一条，也就是会把request等信息传递给SomeView.as_view()方法。因为SomeView继承自View，而我们没有去实现as_view()方法

，那么也就是View.as_view()会进行处理。

而处理的过程如下，解释标注在下面代码中：

 @classonlymethod    def as_view(cls, **initkwargs):        """        Main entry point for a request-response process.        """        for key in initkwargs: #首先是判断 在urlpatterns中as_view有没有传入 http方法的参数，比如我传入一个 get='post',            if key in cls.http_method_names: #如果传入了呢，则会抛出异常，                raise TypeError("You tried to pass in the %s method name as a "                                "keyword argument to %s(). Don't do that."                                % (key, cls.__name__))            if not hasattr(cls, key): #如果传入的参数并不存在于 视图类中，比如我传入 temp='123',而我的视图类中并没有该属性，也会抛出异常                raise TypeError("%s() received an invalid keyword %r. as_view "                                "only accepts arguments that are already "                                "attributes of the class." % (cls.__name__, key))        def view(request, *args, **kwargs): #此方法主要用于返回请求的 视图            self = cls(**initkwargs)             if hasattr(self, 'get') and not hasattr(self, 'head'):#如果类视图实现了 get方法，并且没实现head方法，则head方法等同于get方法                self.head = self.get            self.request = request            self.args = args            self.kwargs = kwargs            return self.dispatch(request, *args, **kwargs) #这是查找类视图中对应方法的重要步骤        view.view_class = cls        view.view_initkwargs = initkwargs        # 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 #把最终的视图处理返回用于调用

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dispatch解释标注在下面代码中

    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:#判断request中的方法是不是类视图允许的方法                                                          #如果是允许的方法，则会在对应的类视图中的方法传给给handler用于之后的处理                                                        #如果是允许的方法，但是类视图中没有实现该方法，则把http_method_not_allowed方法返回            handler = getattr(self, request.method.lower(), self.http_method_not_allowed)        else:#是不允许的方法，则返回 http_method_not_allowed方法，源码在开头            handler = self.http_method_not_allowed        return handler(request, *args, **kwargs)

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