使用 POST 时 Django 中的 MultiValueDictKeyError

When I am using GET, everything works fine. But when I am using POST, I get MultiValueDictKeyError. I don't know why.

View.py

    from rest_framework.response import Response
    from django.contrib.auth import authenticate
    from rest_framework.authtoken.models import Token
    from rest_framework import status
    from django.contrib.auth.models import User
    from rest_framework.authentication import TokenAuthentication
    from rest_framework.permissions import IsAuthenticated
    from django.contrib.auth.signals import user_logged_in, user_logged_out
    from rest_framework.decorators import api_view, authentication_classes, permission_classes
    from django.views.decorators.csrf import csrf_exempt, requires_csrf_token
    @csrf_exempt
    @requires_csrf_token
    @api_view(['POST'])
    def create_user_view(request):
        if request.method == 'POST':
            username = request.POST['username']
            email = request.POST['email']
            password = request.POST['password']
            user = User.objects.create_user(username=username, email=email,     password=password)
            user.save()
            return Response({'detail': "Create user"})


    @csrf_exempt
    def login_view(request):
         if request.method == 'POST':
            username = request.POST['username']
            password = request.POST['password']
            user = authenticate(username=username, password=password)
         if user is not None:
            user_logged_in.send(sender=user.__class__, request=request, user=user)
            token = Token.objects.get_or_create(user=user)
            return Response({
                           'detail': 'POST answer', 'token': token[0].key,
                           })
        else:
            return Response({'detail': "The username or password were incorrect.",
           status: status.HTTP_404_NOT_FOUND})

    @csrf_exempt
    def logout_view(request):
        if request.method == 'POST':
            user = getattr(request, 'user', None)
            if hasattr(user, 'is_authenticated') and not user.is_authenticated():
                user = None
                user_logged_out.send(sender=user.__class__, request=request, user=user)
            if hasattr(request, 'user'):
                 from django.contrib.auth.models import AnonymousUser

                 request.user = AnonymousUser()
           return Response({'detail': "You have logged out successfully."})

Test_app/Urls.py

    from django.conf.urls import patterns, url
    from rest_framework.urlpatterns import format_suffix_patterns
    from test_app import views
    urlpatterns = patterns('test_app.views',
                           url(r'^signup', views.create_user_view),
                           url(r'^login', views.login_view),
                           url(r'^logout', views.logout_view),
                           url(r'^auth', views.AuthView),
                           )
    urlpatterns = format_suffix_patterns(urlpatterns)

Models.py(是的，我只在文件中放了两行)

    from django.contrib.auth.models import User
    from django.db import models

我还按照教程中的说明修改了 settings.py.

Request Method: POST
Request URL:    http://127.0.0.1:8000/signup?username=haha&email=haha@gmail.com&password=okok
Django Version: 1.8.2
Exception Type: MultiValueDictKeyError
Exception Value:    
"'username'"
Exception Location: /Users/wyq/PycharmProjects/env/lib/python2.7/site-packages/django/utils/datastructures.py in __getitem__, line 322