# 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":{}
}
```