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+# Messaging
+
+Messaging (`lv_msg`) is a classic []publisher subscriber](https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern) implementation for LVGL.
+
+## IDs
+Both the publishers and the subscribers needs to know the message identifiers.
+In `lv_msg` these are simple `uint32_t` integers. For example:
+```c
+#define MSG_DOOR_OPENED             1
+#define MSG_DOOR_CLOSED             2
+#define MSG_USER_NAME_CHANGED       100
+#define MSG_USER_AVATAR_CHANGED     101
+```
+
+You can orgnaize the message IDs as you wish.
+
+Both parties also need to know about the format of teh payload. E.g. in the above example
+`MSG_DOOR_OPENED` and `MSG_DOOR_CLOSED` has no payload but `MSG_USER_NAME_CHANGED` can have a `const char *` payload containing the user name, and `MSG_USER_AVATAR_CHANGED` a `const void *` image source with the new avatar image.
+
+
+## Send message
+
+Messages can be sent with `lv_msg_send(msg_id, payload)`. E.g.
+```c
+lv_msg_send(MSG_USER_DOOR_OPENED, NULL);
+lv_msg_send(MSG_USER_NAME_CHANGED, "John Smith");
+```
+
+## Subscribe to a message
+
+`lv_msg_subscribe(msg_id, callback, user_data)` can be used to subscribe to message.
+
+The callback should look like this:
+```c
+
+static void user_name_subscriber_cb(void * s, lv_msg_t * m)
+{
+    /*s: a subscriber obeject, can be used to unscubscribe*/
+    /*m: a message object with the msg_id, payload, and user_data (set durung subscription)*/
+
+    ...do something...
+}
+```
+
+From `lv_msg_t` the followings can be used to get some data:
+- `lv_msg_get_id(m)`
+- `lv_msg_get_payload(m)`
+- `lv_msg_get_user_data(m)`
+
+## Subscribe with an lv_obj
+It's quite typical that an LVGL widget is interested in some messages.
+To make it simpler `lv_msg_subsribe_obj(msg_id, obj, user_data)` can be used.
+If a new message is published with `msg_id` an `LV_EVENT_MSG_RECEIVED` event will be sent to the object.
+
+For example:
+```c
+lv_obj_add_event_cb(user_name_label, user_name_label_event_cb, LV_EVENT_MSG_RECEIVED, NULL);
+lv_msg_subsribe_obj(MSG_USER_NAME_CHANGED, user_name_label, NULL);
+
+...
+
+void user_name_label_event_cb(lv_event_t * e)
+{
+    lv_obj_t * label = lv_event_get_target(e);
+    lv_msg_t * m = lv_event_get_msg(e);
+    lv_label_set_text(label, lv_msg_get_payload(m));
+}
+
+```
+
+### Unsubscribe
+`lv_msg_subscribe` returns a pointer which can be used to unsubscribe:
+```c
+void * s1;
+s1 = lv_msg_subscribe(MSG_USER_DOOR_OPENED, some_callback, NULL);
+
+...
+
+lv_msg_unsubscribe(s1);
+```
+
+## Example
+
+```eval_rst
+
+.. include:: ../../examples/others/msg/index.rst
+
+```
+## API
+
+
+```eval_rst
+
+.. doxygenfile:: lv_msg.h
+  :project: lvgl
+
+```