[1.7.x] Added notes on registering signals in ready() and using dispatch_uid.

Refs #23641.

Backport of d66bda60590daabe21f60a532a613a31a10fedbd from master

1 files changed, 9 insertions, 0 deletions

diff --git a/docs/ref/signals.txt b/docs/ref/signals.txt
index ee1b4903c4..c0f822b1a9 100644
--- a/docs/ref/signals.txt
+++ b/docs/ref/signals.txt
@@ -512,6 +512,15 @@ For example, you could register a callback in an
         def ready(self):
             post_migrate.connect(my_callback, sender=self)
 
+.. note::
+
+    If you provide an :class:`~django.apps.AppConfig` instance as the sender
+    argument, please ensure that the signal is registered in
+    :meth:`~django.apps.AppConfig.ready`. ``AppConfig``\s are recreated for
+    tests that run with a modified set of :setting:`INSTALLED_APPS` (such as
+    when settings are overridden) and such signals should be connected for each
+    new ``AppConfig`` instance.
+
 post_syncdb
 -----------