I wrote a code like this:

List ProductsList;
//...
void initState() {
  super.initState();
  _firestore.collection("Products").snapshots().listen((event) {
    setState(() {
      ProductsList = event.docs;
    });
  });
}
//...
StreamBuilder(
  stream: ProductsList.where((x) => x["Name"] == SearchText).toList().first, // Filter
  builder: (BuildContext context, snapshot) {
    if (snapshot.hasData) {
      return ListView.builder(
        itemCount: snapshot.data.docs.length,
        itemBuilder: (context, index) {
          return Card(
            child: ListTile(
              title: Text(snapshot.data.docs[index].data()["Name"]),
            ),
          );
        },
      );
    } else {
      return Text("No data");
    }
  }
),

My aim is to fetch the Name value from the Arrays in the list. But when I run the code I get an error like this:

I tested it and the results are in the list. How can I to solve the problem? Thanks for help.

CodePudding user response：

Your ProductsList variable is declared, but not defined. You set the ProductList in the listener in initState, but it only gets set if a change is made in your Products Collection. This is why it can't call the .where on ProductList, because it's null after the initState.

You either give ProductsList a default Value

List ProductList = [];

or you pass the stream into the StreamBuilder and change your logic inside the builder

StreamBuilder(
  stream: _firestore.collection("Products").snapshots(),