CBV（class base views）之继承View源码解析
CBV继承View 之View源码解析：
CBV：基于类的视图，就是在视图里使用类处理请求。
优点：继承了所有面向对象的属性(继承、封装、多态)。
CBV提供了一个静态方法as_view(),调用这个方法会创建一个实例，然后再调用dispatch()方法，dispatch()会根据request的method的不同，从而调用相对应的方法来处理request(get,post....)。
View的属性和方法如下：
- 属性
- args
- kwargs
- request
- http_method_names
- 方法
- as_view
- setup
- dispatch
- http_method_not_allowed
- options
- 默认支持options请求
- 显示此接口都支持哪些请求
在源码中带了注释，方便各位学习：
class View:
"""
Intentionally simple parent class for all views. Only implements
dispatch-by-method and simple sanity checking.
"""
# view中所有请求方法的名字
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 kwargs.items():
setattr(self, key, value)
@classonlymethod # 此类方法仅仅在类中能被使用
def as_view(cls, **initkwargs): # **initkwargs: 能接收关键字参数
"""Main entry point for a request-response process."""
for key in initkwargs:
if key in cls.http_method_names: # 如果key是该方法内的请求方法名字
# 翻译：您试图将%s方法名作为“”关键字参数传递给%s（）。别这么做。”
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): # key 必须是已存在的属性
# 翻译：“%s（）收到一个无效的关键字%r。as_view”“只接受已经是该类的”“属性的参数。
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) # 构建一个对象
# 如果有get方法同时没有head方法
if hasattr(self, 'get') and not hasattr(self, 'head'):
# 则 head方法 与 get方法相同
self.head = self.get
# 跳转函数 >> setup >> 初始化所有视图方法共享的属性，记录参数 self.request = request
self.setup(request, *args, **kwargs)
# 如果没有request，报异常
if not hasattr(self, 'request'):
# 翻译：如果没有request，你是不是重写了setup()，并且没有调用super().
raise AttributeError(
"%s instance has no 'request' attribute. Did you override "
"setup() and forget to call super()?" % cls.__name__
)
# 获取所有属性之后进入dispatch函数
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 setup(self, request, *args, **kwargs):
"""Initialize attributes shared by all view methods."""
self.request = request
self.args = args
self.kwargs = kwargs
def dispatch(self, request, *args, **kwargs):
# 翻译：尝试调度到正确的方法；如果方法不存在，
# 遵循错误处理程序。如果请求方法不在已批准的列表中，也要遵循错误处理程序
# 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.
# 判断 请求方法名字 小写是否在 view中所有请求方法
if request.method.lower() in self.http_method_names:
# 获取到我们自己编写的方法(函数，key值，default=默认值),没有则调用默认值
handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
else:
# 请求方法不在View内置请求方法中，跳转下一个函数 >> 请求方法不被允许
handler = self.http_method_not_allowed
# 调用对应的方法
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}
)
# 返回的HttpResponseNotAllowed子类，请求方法不被允许
return HttpResponseNotAllowed(self._allowed_methods())
def options(self, request, *args, **kwargs):
# 处理对选项HTTP谓词的请求的响应
"""Handle responding to requests for the OPTIONS HTTP verb."""
response = HttpResponse()
# 默认支持option请求
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)]
