如何从 Firebase Firestore 集合中指定文档的特定字段获取数据并将其显示到我的 UI？

Question

I tried the code below but in the String quantity = snapshot.data()['Quantity'];function, it returns an error that says The method '[]' can't be unconditionally invoked because the receiver can be 'null'. But when I tried to add a null check to it, it returns another error that says The operator '[]' isn't defined for the type 'Object'. How do I make this function work? I'm trying to get data from the field 'Quantity' from the document typed in the Textfield I made and return a BottomSheet that shows the current quantity in the database.

Future<void> _fabFunction(String dropdownValue, String quantityController) async{
    DocumentReference docRef = FirebaseFirestore.instance.collection('RAWWillyJKT').doc(_textfieldValue.text);

    docRef.get().then((DocumentSnapshot snapshot){
      if (snapshot.exists){
        Object? data = snapshot.data();
        String quantity = snapshot.data()['Quantity'];
        _scaffoldKey.currentState?.showBottomSheet((context) => Container(
          height: 300,
          child: Column(
            children: [
              Text('$quantity'),
              TextButton(
                  onPressed: () {
                    Navigator.pop(context);
                  },
                  child: const Text('Dismiss'))
            ],
          ),
        ));
        return snapshot.data();
      } else {
        FirebaseFirestore.instance
            .collection('RAWWillyJKT')
            .doc(_selectedOption)
            .set({
          'Jenis': _selectedOption,
          'Quantity': quantityController,
          'Metric': dropdownValue,
        });
      }
    });
  }

Answer 1

You declare data variable as Object? and with this type there is no [] operator. The result of data() (if you don't use a converter) is Map<String, dynamic>? which does have the [] operator.

So if you already made sure that the data is not null, you can use:

final data = snapshot.data()!;

After this you can access the fields:

data['Quantity']