我正在尝试使用Flutter和Firebase构建聊天应用程序,我从Github上获取了以下代码并在我的项目中使用。在早期版本的Flutter上,它可以正常工作,在2.0上会显示以下错误:The argument type 'StreamTransformer<dynamic, dynamic>' can't be assigned to the parameter type 'StreamTransformer<QuerySnapshot, List<Message>>'
该错误由以下行触发:
.transform(Utils.transformer(User.fromJson));
完整代码:
class FirebaseApi {
static Stream<List<User>> getUsers() => FirebaseFirestore.instance
.collection('users')
// .collection('ch ats')
.orderBy(UserField.timestamp, descending: true)
.snapshots()
.transform(Utils.transformer(User.fromJson));
static Future uploadMessage(String idUser, String message) async {
final refMessages =
FirebaseFirestore.instance.collection('chats/$idUser/messages');
final newMessage = Message(
// idUser: myId,
idUser: Globals.auth.currentUser!.uid,
// urlAvatar: myUrlAvatar,
urlAvatar: ChatPageState.photoUrl.toString(),
// username: myUsername,
username: ChatPageState.displayName.toString(),
message: message,
createdAt: DateTime.now(),
);
await refMessages.add(newMessage.toJson());
final refUsers = FirebaseFirestore.instance.collection('users');
await refUsers.doc(idUser).update({UserField.timestamp: DateTime.now()});
}
static Stream<List<Message>> getMessages(String idUser) {
return FirebaseFirestore.instance
.collection('chats/$idUser/messages')
.orderBy(MessageField.createdAt, descending: true)
.snapshots()
.transform(Utils.transformer(Message.fromJson));
}
}
class Utils {
static StreamTransformer transformer<T>(
T Function(Map<String, dynamic> json) fromJson) =>
StreamTransformer<QuerySnapshot, List<T>>.fromHandlers(
handleData: (QuerySnapshot data, EventSink<List<T>> sink) {
final snaps = data.docs.map((doc) => doc.data()).toList();
final users = snaps.map((json) => fromJson(json)).toList();
sink.add(users);
},
);
static DateTime toDateTime(Timestamp value) {
// if (value == null);
return value.toDate();
}
static dynamic fromDateTimeToJson(DateTime date) {
if (date == null) return null;
return date.toUtc();
}
}
snapshots.map((e){ // add logo })
代替transform... - Patrick Waweru