Flutter error: Exception caught by gesture The following _CastError was thrown while handling a gesture:Null check operator used on a null value

Question

I'm quite new with flutter, and I'm trying to write a messaging app. So, when I try to navigate from user search screen to chatting screen, I get this error. Full error:

Exception caught by gesture The following _CastError was thrown while handling a gesture: Null check operator used on a null value

and here's my source code:

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import '../screens/Chat_s.dart';

class MessageSearchScreen extends StatefulWidget {
  @override
  _MessageSearchScreenState createState() => _MessageSearchScreenState();
}

class _MessageSearchScreenState extends State<MessageSearchScreen> with WidgetsBindingObserver {
  Map<String, dynamic>? userMap;
  bool isLoading = false;
  final TextEditingController _search = TextEditingController();
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final FirebaseFirestore _firestore = FirebaseFirestore.instance;

  @override

  String chatRoomId(String user1, String user2) {
    if (user1[0].toLowerCase().codeUnits[0] >
        user2.toLowerCase().codeUnits[0]) {
      return "$user1$user2";
    } else {
      return "$user2$user1";
    }
  }

  void onSearch() async {
    FirebaseFirestore _firestore = FirebaseFirestore.instance;

    setState(() {
      isLoading = true;
    });

    await _firestore
        .collection('users')
        .where("email", isEqualTo: _search.text)
        .get()
        .then((value) {
      setState(() {
        userMap = value.docs[0].data();
        isLoading = false;
      });
      print(userMap);
    });
  }

  @override
  Widget build(BuildContext context) {
    final size = MediaQuery.of(context).size;

    return Scaffold(
      appBar: AppBar(
        title: Text("Home Screen"),
      ),
      body: isLoading
          ? Center(
        child: Container(
          height: size.height / 20,
          width: size.height / 20,
          child: CircularProgressIndicator(),
        ),
      )
          : Column(
        children: [
          SizedBox(
            height: size.height / 20,
          ),
          Container(
            height: size.height / 14,
            width: size.width,
            alignment: Alignment.center,
            child: Container(
              height: size.height / 14,
              width: size.width / 1.15,
              child: TextField(
                controller: _search,
                decoration: InputDecoration(
                  hintText: "Search",
                  border: OutlineInputBorder(
                    borderRadius: BorderRadius.circular(10),
                  ),
                ),
              ),
            ),
          ),
          SizedBox(
            height: size.height / 50,
          ),
          ElevatedButton(
            onPressed: onSearch,
            child: Text("Search"),
          ),
          SizedBox(
            height: size.height / 30,
          ),
          if (userMap != null) ListTile(
            onTap: () {
              String roomId = chatRoomId(
                  _auth.currentUser!.displayName!,
                  userMap!['firstName']);

              Navigator.of(context).push(
                MaterialPageRoute(
                  builder: (_) => ChatRoom(
                    chatRoomId: roomId,
                    userMap: userMap!,
                  ),
                ),
              );
            },

            leading: Icon(Icons.account_box, color: Colors.black),
            title: Text(
              userMap!['firstName'],
              style: TextStyle(
                color: Colors.black,
                fontSize: 17,
                fontWeight: FontWeight.w500,
              ),
            ),
            subtitle: Text(userMap!['email']),
            trailing: Icon(Icons.chat, color: Colors.black),
          ) else Container(),
        ],
      ),
    );
  }
}

Can someone help me with this?

Answer 1

i also face same issue then i clear flutter cache (use cammonds flutter clean and then flutter analyze ) and re-install app then work