一、APIView类源码解析

1、APIView是REST framework提供的所有视图的基类，继承自Django的View父类。

2、APIView与 View的不同之处在于：

3、APIView新增了类属性

二、首先是View类的源码解析

View类核心代码在as_view和dispatch方法中，其中as_view是类方法（@classonlymethod），只能通过类调用，不能通过对象调用，它是类视图的入口点。注意这里调用的时候是通过类名.as_view()调用的。

我的路由

urlpatterns=[
    re_path('^channels/$',views.ChannelsAPIView.as_view()),
]

我的视图

class ChannelsAPIView(View):
    def get(self, request):
        '''
        GET  /channels/
        查询所有的频道信息
        :param request:
        :return:
        '''
        channel_queryset = NewsChannel.objects.all()

        channel_list = []

        for channel in channel_queryset:
            channel_list.append({
                'id': channel.id,
                'name': channel.name,
                'url': channel.url
            })

        return JsonResponse(channel_list,safe=False)

    def post(self,request):
        return JsonResponse({‘message’：‘post方法’})

1、接下来看as_view()源码：

def as_view():
	pass
	def view()
		pass
	return view

    @classonlymethod													表示当前方法为类方法，并且只能类去调用
    def as_view(cls, **initkwargs):										initkwargs为字典
        """Main entry point for a request-response process."""
        for key in initkwargs:								
            if key in cls.http_method_names:						    判断key（请求方法）是否在http_method_names中，如果不在抛出异常
                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):												参数名称必须式类已有属性
                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)													实例化当前类的对象
            if hasattr(self, 'get') and not hasattr(self, 'head'):
                self.head = self.get
            self.setup(request, *args, **kwargs)
            if not hasattr(self, 'request'):
                raise AttributeError(
                    "%s instance has no 'request' attribute. Did you override "
                    "setup() and forget to call super()?" % cls.__name__
                )
            return self.dispatch(request, *args, **kwargs)					实现功能：方法派发
        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

2、接下来看dispatch()源码：

if request.method.lower() in self.http_method_names:					
            handler = getattr(self, request.method.lower(), self.http_method_not_allowed)

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)

总结：1、整个as_view方法是一个装饰器函数，它返回内部函数view，所以as_view()执行其实就是内部函数view执行。内部函数view主要逻辑就是：as_view()=>view()=>dispatch()=>相应的http方法

总结：2、dispatch主要完成http请求方法的派发，调用视图类对应实例方法处理用户请求，所有用户需要定义和http请求方法同名的实例方法完成功能，所以一般CBV的模块写法是：

注意：django的CBV本质上来说就是FBV

from django.views import View

class ChannelsAPIView(View):
    def get(self, request):
        return JsonResponse({‘message’：‘get方法’})
    def post(self,request):
        return JsonResponse({‘message’：‘post方法’})
    def put(self,request):
        return JsonResponse({‘message’：‘put方法’})
    def delete(self,request):
        return JsonResponse({‘message’：‘delete方法’})

三、APIView源码解析

我的路由

urlpatterns=[
    re_path('^channels/$',views.ChannelsAPIView.as_view()),
]

我的视图

from rest_framework.response import Response
from rest_framework.views import APIView

class ChannelsAPIView(APIView):
    def get(self, request):
        '''
        GET  /channels/
        查询所有的频道信息
        :param request:
        :return:
        '''
        channel_queryset = NewsChannel.objects.all()

        channel_list = []

        for channel in channel_queryset:
            channel_list.append({
                'id': channel.id,
                'name': channel.name,
                'url': channel.url
            })

        return JsonResponse(channel_list,safe=False)

    def post(self,request):
        return Response({‘message’：‘post方法’})

1、as_view()源码

@classmethod
    def as_view(cls, **initkwargs):
        """
        Store the original class on the view function.

        This allows us to discover information about the view when we do URL
        reverse lookups.  Used for breadcrumb generation.
        """
        if isinstance(getattr(cls, 'queryset', None), models.query.QuerySet):				如果他是QuerySet的一个实例
            def force_evaluation():
                raise RuntimeError(	                翻译：不要直接计算“.queryset”属性，因为结果将被缓存并在请求之间重用请改用“.all（）”或调用“.get_queryset（）
                    'Do not evaluate the `.queryset` attribute directly, '
                    'as the result will be cached and reused between requests. '
                    'Use `.all()` or call `.get_queryset()` instead.'
                )
            
            强制性把属性拿过来
            cls.queryset._fetch_all = force_evaluation

		该走这里了，调用父类的as_view() --- 父类的as_view()核心是dispatch() >> 跳转到dispatch()
        view = super().as_view(**initkwargs)											调用父类（View）的as_view()方法；
        view.cls = cls
        view.initkwargs = initkwargs

        # Note: session based authentication is explicitly CSRF validated,
        # all other authentication is CSRF exempt.

		豁免csrf检测, 返回view
        return csrf_exempt(view)				函数里面套函数，这个一个装饰器！！！

2、dispatch()源码

ChannelsAPIView类中没有定义dispatch方法，但父类APIView和View都实现了dispatch方法，那么继承那个dispatch方法呐？
根据__mro__先继承APIView中的dispatch方法

源代码代码步骤

def dispatch(self, request, *args, **kwargs):
        """
        `.dispatch()` is pretty much the same as Django's regular dispatch,
        but with extra hooks for startup, finalize, and exception handling.
        """
        self.args = args
        self.kwargs = kwargs
        request = self.initialize_request(request, *args, **kwargs)
        self.request = request
        self.headers = self.default_response_headers  # deprecate?

        try:
            self.initial(request, *args, **kwargs)

            # Get the appropriate handler method
            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

            response = handler(request, *args, **kwargs)

        except Exception as exc:
            response = self.handle_exception(exc)

        self.response = self.finalize_response(request, response, *args, **kwargs)
        return self.response

3、initialize_request源码

def initialize_request(self, request, *args, **kwargs):
        """
        Returns the initial request object.
        """
        parser_context = self.get_parser_context(request)

        return Request(
            request,
            parsers=self.get_parsers(),
            authenticators=self.get_authenticators(),
            negotiator=self.get_content_negotiator(),
            parser_context=parser_context
        )

4、Request源码(部分代码)

class Request:
    """
    Wrapper allowing to enhance a standard `HttpRequest` instance.

    Kwargs:
        - request(HttpRequest). The original request instance.
        - parsers(list/tuple). The parsers to use for parsing the
          request content.
        - authenticators(list/tuple). The authenticators used to try
          authenticating the request's user.
    """

    def __init__(self, request, parsers=None, authenticators=None,
                 negotiator=None, parser_context=None):
        assert isinstance(request, HttpRequest), (
            'The `request` argument must be an instance of '
            '`django.http.HttpRequest`, not `{}.{}`.'
            .format(request.__class__.__module__, request.__class__.__name__)
        )

        self._request = request
        self.parsers = parsers or ()
        self.authenticators = authenticators or ()
        self.negotiator = negotiator or self._default_negotiator()
        self.parser_context = parser_context
        self._data = Empty
        self._files = Empty
        self._full_data = Empty
        self._content_type = Empty
        self._stream = Empty
        ......
        ......
        ......
    @property
    def query_params(self):
        """
        More semantically correct name for request.GET.
        """
        return self._request.GET

    @property
    def data(self):
        if not _hasattr(self, '_full_data'):
            self._load_data_and_files()
        return self._full_data

    @property
    def user(self):
        """
        Returns the user associated with the current request, as authenticated
        by the authentication classes provided to the request.
        """
        if not hasattr(self, '_user'):
            with wrap_attributeerrors():
                self._authenticate()
        return self._user
    ......
    ......
    ......

例如：

5、initial(): 源码

源码步骤：

    def initial(self, request, *args, **kwargs):
        """
        Runs anything that needs to occur prior to calling the method handler.
        """
        获取格式化的后缀
        self.format_kwarg = self.get_format_suffix(**kwargs)

        # Perform content negotiation and store the accepted info on the request

		设置内容协商并存储请求中已接受的信息
        neg = self.perform_content_negotiation(request)

		执行
        request.accepted_renderer, request.accepted_media_type = neg

        # Determine the API version, if versioning is in use.

		设置决策版本
        version, scheme = self.determine_version(request, *args, **kwargs)
        执行确定版本
        request.version, request.versioning_scheme = version, scheme

        # Ensure that the incoming request is permitted
        
        执行认证，检查权限，检查限流
        self.perform_authentication(request)
        self.check_permissions(request)
        self.check_throttles(request)

6、finalize_response: 源码

def finalize_response(self, request, response, *args, **kwargs):
        """
        Returns the final response object.
        """
        # Make the error obvious if a proper response is not returned
        assert isinstance(response, HttpResponseBase), (
            'Expected a `Response`, `HttpResponse` or `HttpStreamingResponse` '
            'to be returned from the view, but received a `%s`'
            % type(response)
        )

        if isinstance(response, Response):
            if not getattr(request, 'accepted_renderer', None):
                neg = self.perform_content_negotiation(request, force=True)
                request.accepted_renderer, request.accepted_media_type = neg

            response.accepted_renderer = request.accepted_renderer
            response.accepted_media_type = request.accepted_media_type
            response.renderer_context = self.get_renderer_context()

        # Add new vary headers to the response instead of overwriting.
        vary_headers = self.headers.pop('Vary', None)
        if vary_headers is not None:
            patch_vary_headers(response, cc_delim_re.split(vary_headers))

        for key, value in self.headers.items():
            response[key] = value

        return response

7、csrf_exempt源码

def csrf_exempt(view_func):
    """Mark a view function as being exempt from the CSRF view protection."""
    # view_func.csrf_exempt = True would also work, but decorators are nicer
    # if they don't have side effects, so return a new function.
    def wrapped_view(*args, **kwargs):
        return view_func(*args, **kwargs)
    wrapped_view.csrf_exempt = True
    return wraps(view_func)(wrapped_view)

翻译：