How to use Variables Cloud Firestore in Flutter (Dart) while doing query

Question

This is my working code:

final Stream<QuerySnapshot> products = FirebaseFirestore.instance
  .collection('products')
  .doc('men')
  .collection('tshirts')
  .snapshots();

This is the code I want but not working:

String val = 'tshirts';
final Stream<QuerySnapshot> products = FirebaseFirestore.instance
      .collection('products')
      .doc('men')
      .collection(val)
      .snapshots();

Error: The instance member 'val' can't be accessed in an initializer. Try replacing the reference to the instance member with a different expression

The bellow code I am using in build widget to show database query results & working fine:

GridView.count(
          physics: const BouncingScrollPhysics(),
          crossAxisCount: 2,
          childAspectRatio: 0.5,
          mainAxisSpacing: 30,
          crossAxisSpacing: 10,
          children: snapshot.data!.docs.map((DocumentSnapshot document) {
            Map<String, dynamic> data =
                document.data()! as Map<String, dynamic>;

            return Visibility(
              child: GestureDetector(
                  onTap: () {
                    Navigator.push(
                        context,
                        PageTransition(
                          type: PageTransitionType.bottomToTop,
                          child: const ProductView(productId: '3453245'),
                        ));
                  },
                  child: Stack(
                    children: [
                      Container(
                        decoration: BoxDecoration(
                            image: DecorationImage(
                                image: NetworkImage('${data['img']}'),
                                fit: BoxFit.cover)),
                      ),
                      Align(
                        alignment: Alignment.bottomLeft,
                        child: SizedBox(
                          height: 70,
                          width: double.infinity,
                          child: Column(
                            crossAxisAlignment: CrossAxisAlignment.start,
                            children: [
                              Container(
                                margin: const EdgeInsets.only(
                                    right: 18, top: 15, left: 5),
                                child: Text(
                                  data['name'].toUpperCase(),
                                  textAlign: TextAlign.left,
                                  style: GoogleFonts.oswald(
                                    color: Colors.black,
                                    fontSize: 15,
                                  ),
                                  overflow: TextOverflow.ellipsis,
                                  maxLines: 1,
                                  softWrap: false,
                                ),
                              ),
                              Container(
                                margin: const EdgeInsets.only(left: 5),
                                child: Text(
                                  '\u{20B9} ${data['price']}',
                                  textAlign: TextAlign.left,
                                  style: const TextStyle(
                                    color: Colors.black,
                                    fontSize: 14,
                                  ),
                                  overflow: TextOverflow.ellipsis,
                                  maxLines: 1,
                                ),
                              )
                            ],
                          ),
                        ).frosted(
                          blur: 7,
                        ),
                      ),
                    ],
                  )),
              visible: true,
            );
          }).toList(),
        )

Peter Haddad · Accepted Answer · 2021-12-22 11:52:07Z

3

You are trying to use val before even initializing the class that is used. You can only access it inside a method or the constructor, example:

@override
void initState() {
    super.initState();
    final Stream<QuerySnapshot> products = FirebaseFirestore.instance.collection('products').doc('men').collection(val).snapshots();
}

answered Dec 22, 2021 at 11:52

Peter Haddad

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2 Comments

Himanshu Bohemia Over a year ago

Then how can I use the variable products outside the initState??

Peter Haddad Over a year ago

@HimanshuBohemia String val = 'tshirts'; this you can declare it as an instance variable, but you can't use val unless the class is initialized.. If you want to use the products variable just make it as an instance variable initially referencing null by using Stream<QuerySnapshot>?

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