firebase searching method with flutter code example

Example: firestore search query flutter

import 'package:flutter/material.dart';
import 'package:firebase_database/firebase_database.dart';
import 'package:firebase_database/ui/firebase_animated_list.dart';

class Db extends StatefulWidget {
  @override
  HomeState createState() => HomeState();
}

class HomeState extends State<Db> {
  List<Item> Remedios = List();
  Item item;
  DatabaseReference itemRef;
  TextEditingController controller = new TextEditingController();
  String filter;

  final GlobalKey<FormState> formKey = GlobalKey<FormState>();

  @override
  void initState() {
    super.initState();
    item = Item("", "");
    final FirebaseDatabase database = FirebaseDatabase.instance; //Rather then just writing FirebaseDatabase(), get the instance.
    itemRef = database.reference().child('Remedios');
    itemRef.onChildAdded.listen(_onEntryAdded);
    itemRef.onChildChanged.listen(_onEntryChanged);
    controller.addListener(() {
  setState(() {
    filter = controller.text;
  });
});
  }

  _onEntryAdded(Event event) {
    setState(() {
      Remedios.add(Item.fromSnapshot(event.snapshot));
    });
  }

  _onEntryChanged(Event event) {
    var old = Remedios.singleWhere((entry) {
      return entry.key == event.snapshot.key;
    });
    setState(() {
      Remedios\[Remedios.indexOf(old)\] = Item.fromSnapshot(event.snapshot);
    });
  }

  void handleSubmit() {
    final FormState form = formKey.currentState;

    if (form.validate()) {
      form.save();
      form.reset();
      itemRef.push().set(item.toJson());
    }
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: new AppBar(
        centerTitle: true,
        backgroundColor: new Color(0xFFE1564B),
      ),
      resizeToAvoidBottomPadding: false,
      body: Column(
        children: <Widget>\[
          new TextField(
          decoration: new InputDecoration(
          labelText: "Type something"
          ),
          controller: controller,
          ),
          Flexible(
            child: FirebaseAnimatedList(
              query: itemRef,
              itemBuilder: (BuildContext context, DataSnapshot snapshot,
                  Animation<double> animation, int index) {
                return  Remedios\[index\].name.contains(filter) || Remedios\[index\].form.contains(filter) ? ListTile(
                  leading: Icon(Icons.message),
                  title: Text(Remedios\[index\].name),
                  subtitle: Text(Remedios\[index\].form),
                ) : new Container();
              },
            ),
          ),
        \],
      ),
    );
  }
}

class Item {
  String key;
  String form;
  String name;

  Item(this.form, this.name);

  Item.fromSnapshot(DataSnapshot snapshot)
      : key = snapshot.key,
        form = snapshot.value\["form"\],
        name = snapshot.value\["name"\];

  toJson() {
    return {
      "form": form,
      "name": name,
    };
  }
}