flutter - 使用 flutter_local_notifications 时，如何在 Flutter 中将 Future<Null> 转换为 Future<dynamic>？

Question

我在 flutter 中使用 flutter_local_notifications 插件，在初始化它时遇到了这个错误。

The argument type 'Future<Null> Function(int, String, String, String)' can't be assigned to the parameter type 'Future<dynamic> Function(int, String?, String?, String?)?'

我使用的代码是:

void main() async {
  SystemChrome.setEnabledSystemUIOverlays([SystemUiOverlay.bottom]);
  WidgetsFlutterBinding.ensureInitialized();

  WidgetsFlutterBinding.ensureInitialized();

  var initializationSettingsAndroid = AndroidInitializationSettings('logo');
  var initializationSettingsIOS = IOSInitializationSettings(
      requestAlertPermission: true,
      requestBadgePermission: true,
      requestSoundPermission: true,
      onDidReceiveLocalNotification:
          (int id, String title, String body, String payload) async {}),//Error on this line
          
        
  var initializationSettings = InitializationSettings(
      android: initializationSettingsAndroid, iOS: initializationSettingsIOS);
  await flutterLocalNotificationsPlugin.initialize(initializationSettings,
      onSelectNotification: (String payload) async {
    if (payload != null) {
      debugPrint('notification payload: ' + payload);
    }
  });
  runApp(MyApp());
}

有没有办法在此函数中将 Future 转换为 Future>？
非常感谢您的帮助。谢谢!

Answer 1

看来您正在使用该软件包的 null safe 版本。

随着 null-safety 和 Nullable 类型的引入，您需要仔细检查包提供的参数。

onDidReceiveLocalNotification 不保证 title、body 和 payload 不会为空。这就是为什么定义在他们的代码中如此，

typedef DidReceiveLocalNotificationCallback 
  = Future<dynamic> Function(int id, String? title, String? body, String? payload);

请注意 ? 符号，它表示它们是 Nullable 类型，因此您应该以相同的方式定义回调。

将您的代码更改为此，

onDidReceiveLocalNotification:
      (int id, String? title, String? body, String? payload) async {})