修复公告列表中用户权限判断错误的情况，抽取代码为 decorator。

announcement/decorators.py

@@ -0,0 +1,43 @@
+# coding=utf-8
+from functools import wraps
+
+from django.http import HttpResponse, HttpResponseRedirect
+from django.shortcuts import render
+
+from utils.shortcuts import error_response, error_page
+
+from account.models import SUPER_ADMIN
+from .models import Announcement
+
+
+def check_user_announcement_permission(func):
+    @wraps(func)
+    def _check_user_announcement_permission(*args, **kwargs):
+        """
+        这个函数检测当前用户能否查看这个公告
+        """
+        # CBV 的情况，第一个参数是self，第二个参数是request
+        if len(args) == 2:
+            request = args[-1]
+        else:
+            request = args[0]
+
+        if "announcement_id" not in kwargs:
+            return error_page(request, u"参数错误")
+        announcement_id = kwargs["announcement_id"]
+
+        try:
+            announcement = Announcement.objects.get(id=announcement_id, visible=True)
+        except Announcement.DoesNotExist:
+            return error_page(request, u"公告不存在")
+
+        # 如果公告是只有部分小组可见的
+        if not announcement.is_global:
+            # 用户必须是登录状态的
+            if not request.user.is_authenticated():
+                return HttpResponseRedirect("/login/")
+            if not announcement.groups.filter(id__in=request.user.group_set.all()).exists():
+                return error_page(request, u"公告不存在")
+        return func(*args, **kwargs)
+
+    return _check_user_announcement_permission