四、视图层

一、HttpResponse

1. 视图函数必须有一个返回值，且返回值数据类型必须是HttpResponse对象

2. 三个HttpResponse对象

a. HttpResponse
b. render
c. redirect

二、JsonResponse

1. 通常前后端数据交互采用json格式字符串（字典）

2. JsonResponse向前端传输字典

from django.http import JsonResponse

def index(request):

user_dict = {'name': 'byx', 'msg': '想放假'}

return JsonResponse(user_dict, json_dumps_params={'ensure_ascii': False})

3. JsonResponse向前端传输其他数据类型

from django.http import JsonResponse

def index(request):

l = [1, 2, 3]

return JsonResponse(l, safe=False)

三、FBV与CBV

1. 定义

FBV：基于函数的视图
CBV：基于类的视图

2. CBV基本写法

a. 视图层

from django.shortcuts import render, HttpResponse, redirect
from django.views import View

class Mylogin(View):

def get(self, request):
print('我是MyLogin里面的get方法')
return render(request, 'login.html')

def post(self, request):
print('我是MyLogin里面的post方法')
return HttpResponse('post')

b. 路由层

urlpatterns = [
url(r'^admin/', admin.site.urls),
# FBV路由写法
url(r'^index/', views.index),
# CBV路由写法
url(r'^login/', views.Mylogin.as_view()),
]

3. CBV特点及源码内部原理

a. 特点

自动根据不同请求方式执行不同方法

b. 源码内部原理

根据接收的request参数，用反射获取到对应的方法。

如果想在视图函数执行之前做一些操作，可以在CBV中定义dispatch方法来拦截

def dispatch(self, request, *args, **kwargs):

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)

4. CBV加装饰器方法（装饰器‘outter’）

a. 直接写在函数上方

from django.views import View
from django.utils.decorators import method_decorator

class Mylogin(View):
                                
@method_decorator(outter)
def get(self, request):
print('我是MyLogin里面的get方法')
return render(request, 'login.html')
                        
def post(self, request):
print('我是MyLogin里面的post方法')
return HttpResponse('post')

b. 写在类上方指定给某个方法装

from django.views import View
from django.utils.decorators import method_decorator

@method_decorator(outter, name='post')
class Mylogin(View):
                                 
        def get(self, request):
                print('我是MyLogin里面的get方法')
                return render(request, 'login.html')
                        
        def post(self, request):
                print('我是MyLogin里面的post方法')
                return HttpResponse('post')

c. 给dispatch方法装

from django.views import View
from django.utils.decorators import method_decorator

@method_decorator(outter, name='dispatch')
class Mylogin(View):
        
        def dispatch(self, request, *args, **kwargs):
                return super().dispatch(request, *args, **kwargs)
        
        def get(self, request):
                print('我是MyLogin里面的get方法')
                return render(request, 'login.html')
                        
        def post(self, request):
                print('我是MyLogin里面的post方法')
                return HttpResponse('post')