Flutter IOS app crashes right as it is opened

Ask Time：2019-11-14T03:16:20 Author：Shreyas Rana

I can build the IOS app from Android studio, and it builds fine. May be unrelated, but the Android build and run works perfectly. I used the commands pod repo update, pod update GoogleSignIn, and pod install to make it work.

Launching lib/main.dart on iPhone 11 Pro Max in debug mode...
log: Must be admin to run 'stream' command
Script started, output file is /dev/null

Script done, output file is /dev/null
Running pod install...
Running Xcode build...
Xcode build done.                                           167.8s

But right after the IOS app opens, it crashes immediately. Here is my doctor summary:

[✓] Flutter (Channel stable, v1.9.1+hotfix.2, on Mac OS X 10.14.4 18E226, locale en-US)

[!] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
    ! Some Android licenses not accepted.  To resolve this, run: flutter doctor --android-licenses
[✓] Xcode - develop for iOS and macOS (Xcode 11.2)
[✓] Android Studio (version 3.5)
[✓] VS Code (version 1.39.2)
[✓] Connected device (1 available)

Here is my code:

import 'dart:async';
import 'package:qr_scanner/info.dart';
//import 'package:url_launcher/url_launcher.dart';
import 'package:flutter/material.dart';
import 'package:barcode_scan/barcode_scan.dart';
import 'package:flutter/services.dart';
import 'package:firebase_database/firebase_database.dart';
import 'package:intl/intl.dart';
import 'package:google_sign_in/google_sign_in.dart';

void main() => runApp(MaterialApp(
      debugShowCheckedModeBanner: false,
      home: HomePage(),
    ));

class HomePage extends StatefulWidget {
  @override
  HomePageState createState() {
    return new HomePageState();
  }
}

class HomePageState extends State<HomePage> {
  String result = "Tap me to sign in!";
  TextEditingController studID = new TextEditingController();
  TextEditingController firstName = new TextEditingController();
  TextEditingController lastName = new TextEditingController();
  final DatabaseReference database = FirebaseDatabase.instance.reference();
  String numEntries = "blah";
  GoogleSignIn _googleSignIn = GoogleSignIn(scopes: ['email']);
  bool _isLoggedIn = false;

  void initState() {
    super.initState();
    if (_isLoggedIn) {
      result = "Tap me to sign in!";
    } else {
      result = "Log in with your School Google account to continue.";
    }
  }

  _login() async {
    try {
      await _googleSignIn.signIn();
      if (_googleSignIn.currentUser.email.split('@')[1] == "***********") {
        setState(() {
          _isLoggedIn = true;
          result = "Tap me to sign in!";
          //        result = _googleSignIn.currentUser.displayName;
        });
      } else {
        _logout();
      }
    } catch (err) {
      print(err);
    }
  }

  _logout() {
    _googleSignIn.signOut();
    setState(() {
      _isLoggedIn = false;
      result = "Please log in with your School Google account to continue.";
//      result = "Log in!";
    });
  }

//  _launchURL( String result) async {
////    const url = result;
//    if (await canLaunch(result)) {
//      await launch(result);
//    } else {
//      throw 'Could not launch $result';
//    }
//  }

  void writeData(String s, String id, String firstName, String lastName,
      String qrResult, String condition) {
    var now = new DateTime.now();
    print(now.month.toString() +
        "/" +
        now.day.toString() +
        "/" +
        now.year.toString() +
        " " +
        DateFormat("H:m:s").format(now));
    database.child(s).set({
      'Timestamp': (now.month.toString() +
          "/" +
          now.day.toString() +
          "/" +
          now.year.toString() +
          " " +
          DateFormat("H:m:s").format(now)),
      'Student ID': id,
      'First Name': firstName,
      'Last Name': lastName,
      'Room Number': qrResult,
      'Contition': condition,
    });
  }

  void readNumEntries() {
    database.child('numEntries').once().then((DataSnapshot snapshot) {
//      return snapshot.value;
      print('Data : ${snapshot.value}');
      numEntries = snapshot.value.toString();
    });
  }

  Future _scanQR() async {
    print("yolo");
    setState(() {
      readNumEntries();
    });

    String id = "";
    for (int x = 0; x < _googleSignIn.currentUser.email.length - 1; x++) {
      String email = _googleSignIn.currentUser.email;
      if (email.substring(x, x + 1) == "1" ||
          email.substring(x, x + 1) == "2" ||
          email.substring(x, x + 1) == "3" ||
          email.substring(x, x + 1) == "4" ||
          email.substring(x, x + 1) == "5" ||
          email.substring(x, x + 1) == "6" ||
          email.substring(x, x + 1) == "7" ||
          email.substring(x, x + 1) == "8" ||
          email.substring(x, x + 1) == "9" ||
          email.substring(x, x + 1) == "0") {
        id += email.substring(x, x + 1);
      }
    }
    id = "11" + id;
    String firstName = _googleSignIn.currentUser.displayName.split(" ")[0];
    String lastName = _googleSignIn.currentUser.displayName.split(" ")[1];
    print(id);
    print(firstName);
    print(lastName);

    try {
      LastRoom room = new LastRoom();
//      room.writeContent("hi1!!!!");
      String qrResult = await BarcodeScanner.scan();
      String condition = "";
      room.readContent().then((onValue) {
        if (onValue == "Check in") {
          condition = "Check Out";
        } else {
          condition = "Check in";
        }
        writeData((int.parse(numEntries) + 1).toString(), id, firstName,
            lastName, qrResult, condition);
        room.writeContent(condition);

        setState(() {
//        result = "https://docs.google.com/forms v35/d/e/1FAIpQLSeX5jxY2oSHea8C2VCmEEj7ZFYG7F7KuPRrX9QHUbXwBIdt_A/viewform?usp=pp_url&entry.693612192=$firstName&entry.1310158676=$lastName&entry.201368718=$id&entry.503158018=$qrResult";
//        result = "https://docs.google.com/forms/d/e/1FAIpQLSeX5jxY2oSHea8C2VCmEEj7ZFYG7F7KuPRrX9QHUbXwBIdt_A/viewform?usp=pp_url&entry.201368718=$id&entry.503158018=$qrResult";
//        _launchURL(result);
          result = "All checked in!\nTap again to check in!";

          database
              .update({'numEntries': (int.parse(numEntries) + 1).toString()});
        });
      });
    } on PlatformException catch (ex) {
      if (ex.code == BarcodeScanner.CameraAccessDenied) {
        setState(() {
//          result = "Camera permission was denied";
        });
      } else {
        setState(() {
//          result = "Unknown Error $ex";
        });
      }
    } on FormatException {
      setState(() {
        result = "Tap me to sign in!";
      });
    } catch (ex) {
      setState(() {
//        result = "Unknown Error $ex";
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.redAccent,
        title: Text("ZipScan"),
      ),
      body:
      Container(

      decoration: new BoxDecoration(

        gradient: LinearGradient(
          // Where the linear gradient begins and ends
          begin: Alignment.topLeft,
          end: Alignment.bottomRight,
          // Add one stop for each color. Stops should increase from 0 to 1
          stops: [0.9, 0.901, 1],
          colors: [
            // Colors are easy thanks to Flutter's Colors class.
            Colors.blueGrey[800],
            Colors.blueGrey[800],
            Colors.blueGrey[800],
          ],
        ),
      ),



        child: Column(
          children: <Widget>[
            _isLoggedIn
                ? Row(
              children: <Widget>[
                Container(
                    margin:
                    const EdgeInsets.only(top: 10, left: 10, right: 10),
                    child: Image.network(
                      _googleSignIn.currentUser.photoUrl,
                      height: 80,
                      width: 80,
                    )),
                Center(
                    child: Column(
                      children: <Widget>[
                        Text(_googleSignIn.currentUser.displayName,
                            style: new TextStyle(
                                fontSize: 15.0, fontWeight: FontWeight.bold, color: Colors.white)),
                        Container(
                          height: 50,
                          width: 150,
                          margin: const EdgeInsets.only(
                              top: 10, left: 10, right: 10),
                          decoration: new BoxDecoration(

                            gradient: LinearGradient(
                              // Where the linear gradient begins and ends
                              begin: Alignment.topLeft,
                              end: Alignment.bottomRight,
                              // Add one stop for each color. Stops should increase from 0 to 1
                              stops: [0.8, 0.801, 1],
                              colors: [
                                // Colors are easy thanks to Flutter's Colors class.
                                Colors.blueGrey[600],
                                Colors.redAccent,
                                Colors.redAccent,
                              ],
                            ),

                            borderRadius: new BorderRadius.only(
                              topLeft: const Radius.circular(20.0),
                              topRight: const Radius.circular(20.0),
                              bottomLeft: const Radius.circular(20.0),
                              bottomRight: const Radius.circular(20.0),
                            ),
                            color: Colors.blueGrey[600],
                          ),
                          child: InkWell(
                            onTap: _logout,
                            child: Center(
                              child: Text("Log Out?",
                                  style: new TextStyle(
                                      fontSize: 15.0,
                                      fontWeight: FontWeight.bold)),
                            )
                          ),
                        )
                      ],
                    ))
              ],
            )
                : Row(
              children: <Widget>[
                Container(
                    margin:
                    const EdgeInsets.only(top: 10, left: 10, right: 10),
                    child: Icon(
                      Icons.account_circle,
                      size: 80,
                    )),
                Container(
                  height: 100,
                  width: 150,
                  margin:
                  const EdgeInsets.only(top: 10, left: 10, right: 10),
                  decoration: new BoxDecoration(

                    gradient: LinearGradient(
                      // Where the linear gradient begins and ends
                      begin: Alignment.topLeft,
                      end: Alignment.bottomRight,
                      // Add one stop for each color. Stops should increase from 0 to 1
                      stops: [0.8, 0.801, 1],
                      colors: [
                        // Colors are easy thanks to Flutter's Colors class.
                        Colors.blueGrey[600],
                        Colors.redAccent,
                        Colors.redAccent,
                      ],
                    ),


                    borderRadius: new BorderRadius.only(
                      topLeft: const Radius.circular(20.0),
                      topRight: const Radius.circular(20.0),
                      bottomLeft: const Radius.circular(20.0),
                      bottomRight: const Radius.circular(20.0),
                    ),
                    color: Colors.blueGrey[600],
                  ),
                  child: InkWell(
                      onTap: _login,
                      child: Center(
                        child: Text("Log In?",
                            style: new TextStyle(
                                fontSize: 15.0,
                                fontWeight: FontWeight.bold)),
                      )),
                )
              ],
            ),
//          Container(
//            padding: EdgeInsets.all(5),
//            margin: const EdgeInsets.only(top: 10, left: 10, right: 10),
////          width: MediaQuery.of(context).size.width-30,
//            decoration: new BoxDecoration(
////            border: new Border.all(color: Colors.black, width: 0.5),
//              borderRadius: new BorderRadius.only(
//                topLeft: const Radius.circular(5.0),
//                topRight: const Radius.circular(5.0),
//                bottomLeft: const Radius.circular(5.0),
//                bottomRight: const Radius.circular(5.0),
//              ),
//              color: Colors.grey[300],
//            ),
//            width: MediaQuery.of(context).size.width,
//            child: Center(
//              child: TextField(
//                controller: FirstName,
//                decoration: new InputDecoration(labelText: "First Name"),
//                keyboardType: TextInputType.text,
//              ),
//            ),
//          ),
//          Container(
//            padding: EdgeInsets.all(5),
//            margin: const EdgeInsets.only(top: 10, left: 10, right: 10),
////          width: MediaQuery.of(context).size.width-30,
//            decoration: new BoxDecoration(
////            border: new Border.all(color: Colors.black, width: 0.5),
//              borderRadius: new BorderRadius.only(
//                topLeft: const Radius.circular(5.0),
//                topRight: const Radius.circular(5.0),
//                bottomLeft: const Radius.circular(5.0),
//                bottomRight: const Radius.circular(5.0),
//              ),
//              color: Colors.grey[300],
//            ),
//            width: MediaQuery.of(context).size.width,
//            child: Center(
//              child: TextField(
//                controller: LastName,
//                decoration: new InputDecoration(labelText: "Last Name"),
//                keyboardType: TextInputType.text,
//              ),
//            ),
//          ),
//          Container(
//            padding: EdgeInsets.all(5),
//            margin: const EdgeInsets.only(top: 10, left: 10, right: 10),
////          width: MediaQuery.of(context).size.width-30,
//            decoration: new BoxDecoration(
////            border: new Border.all(color: Colors.black, width: 0.5),
//              borderRadius: new BorderRadius.only(
//                topLeft: const Radius.circular(5.0),
//                topRight: const Radius.circular(5.0),
//                bottomLeft: const Radius.circular(5.0),
//                bottomRight: const Radius.circular(5.0),
//              ),
//              color: Colors.grey[300],
//            ),
//            width: MediaQuery.of(context).size.width,
//            child: Center(
//              child: TextField(
//                controller: studID,
//                decoration: new InputDecoration(labelText: "Enter your ID"),
//                keyboardType: TextInputType.number,
//              ),
//            ),
//          ),

            InkWell(
                onTap: () {
                  _isLoggedIn ? _scanQR() : print("Log in!!");
                },
//              _scanQR,
                child: Container(
                    padding: EdgeInsets.all(5),
                    margin: const EdgeInsets.only(top: 10, left: 10, right: 10),
//          width: MediaQuery.of(context).size.width-30,
                    decoration: new BoxDecoration(


                      gradient: LinearGradient(
                        // Where the linear gradient begins and ends
                        begin: Alignment.topLeft,
                        end: Alignment.bottomRight,
                        // Add one stop for each color. Stops should increase from 0 to 1
                        stops: [0.85, 0.851, 1],
                        colors: [
                          // Colors are easy thanks to Flutter's Colors class.
                          Colors.blueGrey[600],
                          Colors.redAccent,
                          Colors.redAccent,
                        ],
                      ),






                      borderRadius: new BorderRadius.only(
                        topLeft: const Radius.circular(5.0),
                        topRight: const Radius.circular(5.0),
                        bottomLeft: const Radius.circular(5.0),
                        bottomRight: const Radius.circular(5.0),
                      ),
                      color: Colors.blueGrey[600],
                    ),
                    width: MediaQuery.of(context).size.width,
                    height: 300,
                    child: Center(
                      child: Text(
                        result,
                        style: new TextStyle(
                            fontSize: 30.0, fontWeight: FontWeight.bold),
                      ),
                    )))
          ],
        ),
      )

      //backgroundColor: Colors.grey,

    );
  }
}

Author:Shreyas Rana，eproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/58844063/flutter-ios-app-crashes-right-as-it-is-opened

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