update formset with class based view - django

Question

i've created web blog with django 2.2 each post has multiple images , but when i try to update the post
images wont updated
i use class based view
class Post(models.Model):
user= models.ForeignKey(Account,on_delete=models.CASCADE)
title= models.CharField(max_length=100)
#others
class PostImage(models.Model):
post= models.ForeignKey(Post,on_delete=models.CASCADE,related_name='images')
media_files = models.FileField(upload_to=random_url)
and this my forms.py
class PostImageForm(forms.ModelForm):
class Meta:
model = PostImage
fields = [
'media_files'
]
class PostUpdateForm(forms.ModelForm):
class Meta:
model = Post
fields = [
'title','description',#and others
]
my views.py
PostImageFormSet = inlineformset_factory(
Post,PostImage,form=PostImageForm,extra=1,can_delete=True,can_order=False
)
class PostUpdateView(LoginRequiredMixin,UserPassesTestMixin,UpdateView):
model = Post
form_class = PostUpdateForm
template_name = 'posts/update_post.html'
def get_context_data(self,**kwargs):
data = super().get_context_data(**kwargs)
if self.request.POST:
data['images'] = PostImageFormSet(self.request.POST or None,self.request.FILES,instance=self.object)
else:
data['images'] = PostImageFormSet(instance=self.object)
return data
def form_valid(self,form):
context = self.get_context_data()
images = context['images']
with transaction.atomic():
if form.is_valid() and images.is_valid():
self.object = form.save()
images.instance = self.object
images.save()
return super().form_valid(form)
def test_func(self):
post = self.get_object()
if self.request.user.username == post.user.username:
return True
return False
def get_success_url(self):
return reverse_lazy('post:post-detail',kwargs={'slug':self.object.slug})
my templates
<form enctype="multipart/form-data" method="post" action="">
{% csrf_token %}
{{images.management_form }}
{{ form|crispy }}
{% for img in images %}
<label>{{img.media_files.label}}</label>
{{img.media_files}}
{% endfor %}
<button type="submit" class="btn btn-block btn-primary">update</button>
</form>
i'm wondering why didnt update the posts image !?
thanks for replay ..