django通用视图View类的源码解析

一般我们使用的形式：

url(r'^post/(?P[0-9]+)/$', views.PostetailView.as_view(), name='detail'),

最后可以看到View是所有通用视图的父类，包括ListView， DetailView等

那as_view()到底实现了什么呢？

先整体看下源码：

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())

    def options(self, request, *args, **kwargs):
        """
        Handles responding to requests for the OPTIONS HTTP verb.
        """
        response = http.HttpResponse()
        response['Allow'] = ', '.join(self._allowed_methods())
        response['Content-Length'] = '0'
        return response

    def _allowed_methods(self):
        return [m.upper() for m in self.http_method_names if hasattr(self, m)]

一、

as_view被@classonlymethod装饰，是类方法。as_view类似一个装饰器，返回了一个view函数。

  def view(request, *args, **kwargs):
  	  # 实例化通用视图
      self = cls(**initkwargs)
      if hasattr(self, 'get') and not hasattr(self, 'head'):
          self.head = self.get
          
      # request，url中的参数成为实例的属性
      self.request = request
      self.args = args
      self.kwargs = kwargs
      return self.dispatch(request, *args, **kwargs)

1、这个view函数使用as_view()的参数对PostetailView（或使用其他通用视图），进行实例化。
2、同时request，url中的参数成为了实例的属性。这个有什么用呢？在响应处理的时候，我们可以直接使用实例的属性。
3、最后调用self.dispatch(request, *args, **kwargs)，入参就是request方法和url参数。

二、

1、dispatch() 函数对reuqest的method字段进行检查，也就是post，get等。
2、然后，查找实例自身的对应的属性，如get/post属性。get/post属性是处理request的方法，相当于我们普通的视图函数如 ：

# 普通的视图函数
def index(request):

3、在DetailView、ListView等通用视图中也就是实例的父类中一般都写好了对用的get、post等方法。如果对intance没有特殊处理，可以直接使用，否则需要重写刚发。

三、

随后我们整体看下，as_view()其实主要是实例化通用视图类，然后返回视图中对应request的方法，这个方法就是处理请求的。