检查 Firebase Firestore 中是否存在密钥

Question

I want to make a to-do list with task due date as an optional field, so I need to check if some tasks have dueDate and add it as a subtitle based on that. How can I check if a field exists inside a doc in a StreamBuilder?

class _TaskListState extends State<TaskList> {
  var myStream;
  @override
  void initState() {
    myStream = FirebaseFirestore.instance
        .collection('tasks')
        .doc(widget.uid)
        .collection('mytasks')
        .snapshots();

    super.initState();
  }

  ...

  void _updateTaskDesc(
      dynamic currTask, String newDesc, DateTime newDate, TimeOfDay newTime) {
    FirebaseFirestore.instance
        .collection('tasks')
        .doc(widget.uid)
        .collection('mytasks')
        .doc(currTask['id'])
        .update({
      'desc': newDesc,
      'dueDate': newDate.toString(),
      'dueTime': newTime.toString(),
    });
  }

  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
      stream: myStream,
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return const Center(
            child: SizedBox(
                height: 100, width: 100, child: CircularProgressIndicator()),
          );
        } else {
          final docs = snapshot.data.docs;
          bool hasDateTime = ????? <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
          return ListView.builder(
            itemCount: docs.length,
            itemBuilder: (ctx, index) {
              final currTask = docs[index];
              return InkWell(
                highlightColor: Theme.of(context).secondaryHeaderColor,
                splashColor: Theme.of(context).secondaryHeaderColor,
                onLongPress: () {
                  showModalBottomSheet<dynamic>(
                    isScrollControlled: true,
                    context: context,
                    builder: (bCtx) {
                      FocusManager.instance.primaryFocus?.unfocus();
                      return TaskOptions(_updateTaskDesc,
                          () => _updateHasImage(docs[index]), currTask);
                    },
                  );
                },
                child: Dismissible(
                  direction: DismissDirection.startToEnd,
                  key: UniqueKey(),
                  onDismissed: (_) async {
                    FirebaseFirestore.instance
                        .collection('tasks')
                        .doc(widget.uid)
                        .collection('mytasks')
                        .doc(currTask['id'])
                        .delete();

                    ScaffoldMessenger.of(context).showSnackBar(
                      SnackBar(
                        content: Text("${currTask['desc']} dismissed"),
                        action: SnackBarAction(
                          label: 'Undo',
                          onPressed: () {
                            FirebaseFirestore.instance
                                .collection("tasks")
                                .doc(widget.uid)
                                .collection("mytasks")
                                .doc(currTask['id'])
                                .set({
                              "desc": currTask['desc'],
                              "id": currTask['id'],
                              "isDone": currTask['isDone'],
                              "hasImage": currTask['hasImage'],
                            });
                            try {
                              FirebaseFirestore.instance
                                  .collection("tasks")
                                  .doc(widget.uid)
                                  .collection("mytasks")
                                  .doc(currTask['id'])
                                  .update({
                                "dueDate": currTask['dueDate'],
                                "dueTime": currTask['dueTime'],
                              });
                            } catch (e) {}
                          },
                        ),
                      ),
                    );
                  },
                  child: ListTile(
                    ...
                    subtitle: Text(hasDateTime
                        ? DateFormat('dd/MM')
                            .format(DateTime.parse(currTask['dueDate']))
                        : ''),
                    ...

I saw that a containsKey('key') method works for some people but I get NoSuchMethod when I try that. What can I do?

Answer 1

The single document is just a normal Dart Map , so you can check if a key exists or not using containsKey method.

So you condition becomes the following:

bool hasDateTime = currTask.containsKey('dueDate`);

NOTE: In the question I can see that you are defining the condition in the wrong place which is outside the itemBuilder method in the ListView so that it is not item based and well not work because it does not make sense.

You can have it in this place:

...
itemBuilder: (ctx, index) {
    final currTask = docs[index];
    bool hasDateTime = currTask.containsKey('dueDate`);
    return InkWell(
...