flutter: type 'String' is not a subtype of type 'List<dynamic>'

Question

I actually have two questions.

I'm trying to add a String type object to an existing array in Firestore like this:

  addWalletToUser(coinAddress) async {
    final FirebaseUser user = (await FirebaseAuth.instance.currentUser());
    try {
      await Firestore.instance.collection('users').document(user.uid)
          .updateData({
            "cryptoAddresses": FieldValue.arrayUnion(coinAddress)
          });
    } catch (e) {
      print('error caught: $e');
      return null;
    }
  }

This results in the following error: flutter: type 'String' is not a subtype of type 'List<dynamic>'

My second question is why my code in this if-statement is carried out while addWalletToUser should return null:

if (addWalletToUser(_textController.text) != null)

Any help will be greatly appreciated!

addWalletToUser function is async so it returns a Future which is not null. What you are returning inside the async function is obtained as await addWalletToUser(text) which will now give null. Also what is the function FieldValue.arrayUnion returning? — Ryosuke
– Ryosuke, Commented Dec 5, 2019 at 11:10
Please limit yourself to a single question per post, so that it can be answered with a single answer. See meta.stackexchange.com/questions/39223/… — Frank van Puffelen
– Frank van Puffelen, Commented Dec 5, 2019 at 14:44

Gazihan Alankus · Accepted Answer · 2019-12-05 11:21:32Z

5

Regarding this error:

flutter: type 'String' is not a subtype of type 'List'

This means you are trying to do assign a String to a List (as in list = string).

The arrayUnion takes a parameter of type List<dynamic>:

  static FieldValue arrayUnion(List<dynamic> elements) =>
      FieldValue._(FieldValueType.arrayUnion, elements);

https://github.com/FirebaseExtended/flutterfire/blob/master/packages/cloud_firestore/cloud_firestore/lib/src/field_value.dart#L35

Therefore you need to do the following:

"cryptoAddresses": FieldValue.arrayUnion(['data1','data2','data3'])

In your case, it's probably going to be:

"cryptoAddresses": FieldValue.arrayUnion([coinAddress])

edited Dec 5, 2019 at 11:21

Gazihan Alankus

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answered Dec 5, 2019 at 11:19

Peter Haddad

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Comments

Jack · Accepted Answer · 2019-12-05 14:51:03Z

0

I solved the second problem by creating a third function:

  Future storeValues(coinAddress) async {
    final walletToUser = await addWalletToUser(coinAddress);
    final wallet = await createWallet(coinAddress);
    return [walletToUser,wallet];
  }

and by calling that function with .then() like so:

 storeValues(_textController.text).then((val) {
                      if (val[0] != null && val[1] != null) {
                      //do something here
}}

answered Dec 5, 2019 at 14:51

Jack

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