# Parse push fields (/en/realtime-media/im/build/notifications-and-event-handling/offline-push/parse-push-fields/flutter)

> For AI agents: see the complete documentation index at [llms.txt](/llms.txt).

After receiving a push notification, you need to parse the data.

    Use the `FirebaseMessaging.instance.getInitialMessage` method to obtain the custom extension fields when the app is opened. The sample code is as follows:

    ```dart
    FirebaseMessaging.instance.getInitialMessage().then((message) {
          Map? data = message?.data;
          if (data != null) {
            String f = data['f'] ?? '';
            String t = data['t'] ?? '';
            String m = data['m'] ?? '';
            String g = data['g'] ?? '';
            Object e = data['e'] ?? '';
          }
    });
    ```

    | Parameter | Description                                              |
    | --------- | -------------------------------------------------------- |
    | `f`       | The user ID of the push notification sender.             |
    | `t`       | The user ID of the push notification recipient.          |
    | `m`       | The message ID: A unique identifier of the message.      |
    | `g`       | The group ID: This field exists only for group messages. |
    | `e`       | The user-defined extension field.                        |

    `e` is a completely user-defined extension. The data source is `em_push_ext.custom` of the message extension. The data structure is as follows:

    ```json
    {
        "em_push_ext": {
            "custom": {
                "key1": "value1",
                "key2": "value2"
            }
        }
    }
    ```

    The data structure of the extension in the `RemoteMessage.data` object is as follows:

    ```dart
    {
        "t":"receiver",
        "f":"fromUsername",
        "m":"msg_id",
        "g":"group_id",
        "e":{}
    }
    ```