29:52: Error: Property 'photoURL' cannot be accessed on 'User?' because it is potentially null
29:52: Error: Property 'photoURL' cannot be accessed on 'User?' because it is potentially null
我正在尝试在我的基本 Flutter 应用程序中添加 google 使用 firebase 身份验证登录，但出现上述错误。我搜索了很多但找不到任何答案，请帮助我。这是我终端中的全部错误：
lib/logged_in_widget.dart:29:52: Error: Property 'photoURL' cannot be accessed on 'User?' because it is potentially null.
- 'User' is from 'package:firebase_auth/firebase_auth.dart' ('../../../../AppData/Local/Pub/Cache/hosted/pub.dartlang.org/firebase_auth-1.4.1/lib/firebase_auth.dart').
Try accessing using ?. instead.
backgroundImage: NetworkImage(user.photoURL!),
^^^^^^^^
lib/logged_in_widget.dart:34:32: Error: Property 'displayName' cannot be accessed on 'User?' because it is potentially null.
- 'User' is from 'package:firebase_auth/firebase_auth.dart' ('../../../../AppData/Local/Pub/Cache/hosted/pub.dartlang.org/firebase_auth-1.4.1/lib/firebase_auth.dart').
Try accessing using ?. instead.
'Name:' + user.displayName!,
^^^^^^^^^^^
FAILURE: Build failed with an exception.
* Where:
Script 'C:\src\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 1070
* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command 'C:\src\flutter\bin\flutter.bat'' finished with non-zero exit value 1
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 21s
Exception: Gradle task assembleDebug failed with exit code 1
我也使用了空安全：
dart pub outdated --mode=null-safety
这是主要代码：
import 'package:yt_firebase2/google_sign_in.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
class LoggedInWidget extends StatelessWidget {
// final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
@override
Widget build(BuildContext context) {
final user = FirebaseAuth.instance.currentUser;
return Scaffold(
appBar: AppBar(
title: Text('Logged In'),
centerTitle: true,
actions: [
TextButton(onPressed: () {}, child: Text('Logout'),)
],
),
body: Container(
alignment: Alignment.center,
color: Colors.blueGrey.shade900,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text('profile', style: TextStyle(fontSize: 24),),
SizedBox(height: 32,),
CircleAvatar(
radius: 40,
backgroundImage: NetworkImage(user.photoURL!),
),
SizedBox(height: 8,),
Text(
'Name:' + user.displayName!,
style: TextStyle(color: Colors.white, fontSize: 16),
)
],
),
)
);
}
}
这是我的 firebase_auth 文件中的代码：
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:google_sign_in/google_sign_in.dart';
class GoogleSignInProvider extends ChangeNotifier{
final googleSign = GoogleSignIn();
GoogleSignInAccount? _user;
GoogleSignInAccount get user => _user!;
Future GoogleLogin() async {
final googleUser = await googleSign.signIn();
if (googleUser == null) return;
_user = googleUser;
final googleAuth = await googleUser.authentication;
final credential = GoogleAuthProvider.credential(
accessToken: googleAuth.accessToken,
idToken: googleAuth.idToken,
);
await FirebaseAuth.instance.signInWithCredential(credential);
notifyListeners();
}
}
这是我的 pubspec.yaml 文件
description: A new Flutter project.
# The following line prevents the package from being accidentally published to
# pub.dev using `flutter pub publish`. This is preferred for private packages.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev
# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1
environment:
sdk: ">=2.15.1 <3.0.0"
# Dependencies specify other packages that your package needs in order to work.
# To automatically upgrade your package dependencies to the latest versions
# consider running `flutter pub upgrade --major-versions`. Alternatively,
# dependencies can be manually updated by changing the version numbers below to
# the latest version available on pub.dev. To see which dependencies have newer
# versions available, run `flutter pub outdated`.
dependencies:
flutter:
sdk: flutter
# The following adds the Cupertino Icons font to your application.
# Use with the CupertinoIcons class for iOS style icons.
cupertino_icons: ^1.0.2
dev_dependencies:
flutter_test:
sdk: flutter
# The "flutter_lints" package below contains a set of recommended lints to
# encourage good coding practices. The lint set provided by the package is
# activated in the `analysis_options.yaml` file located at the root of your
# package. See that file for information about deactivating specific lint
# rules and activating additional ones.
flutter_lints: ^1.0.0
cupertino_icons: ^1.0.2
firebase_auth: ^1.1.4
google_sign_in: ^5.0.3
font_awesome_flutter: ^9.0.0
provider: ^5.0.0
# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec
# The following section is specific to Flutter.
flutter:
# The following line ensures that the Material Icons font is
# included with your application, so that you can use the icons in
# the material Icons class.
uses-material-design: true
# To add assets to your application, add an assets section, like this:
# assets:
# - images/a_dot_burr.jpeg
# - images/a_dot_ham.jpeg
# An image asset can refer to one or more resolution-specific "variants", see
# https://flutter.dev/assets-and-images/#resolution-aware.
# For details regarding adding assets from package dependencies, see
# https://flutter.dev/assets-and-images/#from-packages
# To add custom fonts to your application, add a fonts section here,
# in this "flutter" section. Each entry in this list should have a
# "family" key with the font family name, and a "fonts" key with a
# list giving the asset and other descriptors for the font. For
# example:
# fonts:
# - family: Schyler
# fonts:
# - asset: fonts/Schyler-Regular.ttf
# - asset: fonts/Schyler-Italic.ttf
# style: italic
# - family: Trajan Pro
# fonts:
# - asset: fonts/TrajanPro.ttf
# - asset: fonts/TrajanPro_Bold.ttf
# weight: 700
#
# For details regarding fonts from package dependencies,
# see https://flutter.dev/custom-fonts/#from-packages
作为旁注：
GoogleSignInAccount? _user;
GoogleSignInAccount get user => _user!;
如果您不能 100% 确定 _user 永远不会为 null，那么这确实不是一个好的做法。但是获取 _user 可能会出错，没有返回任何值。
你的问题：
NetworkImage() 需要一个 String（不可为 null 的类型）！在您的代码 NetworkImage(user.photoURL!), 中，您通过使用 bang 运算符 (!) 告诉 dart 它在逻辑上永远不能为 null 来做到这一点。
displayName 也是如此，因为 Text() 也 requires a String 不是字符串？ --> 这就是 nullsafety 的全部要点：在 运行 时间内避免 null 错误。
解法：
确保GoogleSignInAccount? _user；在任何地方引用它之前不为空
在你的代码中。
我正在尝试在我的基本 Flutter 应用程序中添加 google 使用 firebase 身份验证登录，但出现上述错误。我搜索了很多但找不到任何答案，请帮助我。这是我终端中的全部错误：
lib/logged_in_widget.dart:29:52: Error: Property 'photoURL' cannot be accessed on 'User?' because it is potentially null.
- 'User' is from 'package:firebase_auth/firebase_auth.dart' ('../../../../AppData/Local/Pub/Cache/hosted/pub.dartlang.org/firebase_auth-1.4.1/lib/firebase_auth.dart').
Try accessing using ?. instead.
backgroundImage: NetworkImage(user.photoURL!),
^^^^^^^^
lib/logged_in_widget.dart:34:32: Error: Property 'displayName' cannot be accessed on 'User?' because it is potentially null.
- 'User' is from 'package:firebase_auth/firebase_auth.dart' ('../../../../AppData/Local/Pub/Cache/hosted/pub.dartlang.org/firebase_auth-1.4.1/lib/firebase_auth.dart').
Try accessing using ?. instead.
'Name:' + user.displayName!,
^^^^^^^^^^^
FAILURE: Build failed with an exception.
* Where:
Script 'C:\src\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 1070
* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command 'C:\src\flutter\bin\flutter.bat'' finished with non-zero exit value 1
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 21s
Exception: Gradle task assembleDebug failed with exit code 1
我也使用了空安全：
dart pub outdated --mode=null-safety
这是主要代码：
import 'package:yt_firebase2/google_sign_in.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
class LoggedInWidget extends StatelessWidget {
// final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
@override
Widget build(BuildContext context) {
final user = FirebaseAuth.instance.currentUser;
return Scaffold(
appBar: AppBar(
title: Text('Logged In'),
centerTitle: true,
actions: [
TextButton(onPressed: () {}, child: Text('Logout'),)
],
),
body: Container(
alignment: Alignment.center,
color: Colors.blueGrey.shade900,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text('profile', style: TextStyle(fontSize: 24),),
SizedBox(height: 32,),
CircleAvatar(
radius: 40,
backgroundImage: NetworkImage(user.photoURL!),
),
SizedBox(height: 8,),
Text(
'Name:' + user.displayName!,
style: TextStyle(color: Colors.white, fontSize: 16),
)
],
),
)
);
}
}
这是我的 firebase_auth 文件中的代码：
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:google_sign_in/google_sign_in.dart';
class GoogleSignInProvider extends ChangeNotifier{
final googleSign = GoogleSignIn();
GoogleSignInAccount? _user;
GoogleSignInAccount get user => _user!;
Future GoogleLogin() async {
final googleUser = await googleSign.signIn();
if (googleUser == null) return;
_user = googleUser;
final googleAuth = await googleUser.authentication;
final credential = GoogleAuthProvider.credential(
accessToken: googleAuth.accessToken,
idToken: googleAuth.idToken,
);
await FirebaseAuth.instance.signInWithCredential(credential);
notifyListeners();
}
}
这是我的 pubspec.yaml 文件
description: A new Flutter project.
# The following line prevents the package from being accidentally published to
# pub.dev using `flutter pub publish`. This is preferred for private packages.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev
# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1
environment:
sdk: ">=2.15.1 <3.0.0"
# Dependencies specify other packages that your package needs in order to work.
# To automatically upgrade your package dependencies to the latest versions
# consider running `flutter pub upgrade --major-versions`. Alternatively,
# dependencies can be manually updated by changing the version numbers below to
# the latest version available on pub.dev. To see which dependencies have newer
# versions available, run `flutter pub outdated`.
dependencies:
flutter:
sdk: flutter
# The following adds the Cupertino Icons font to your application.
# Use with the CupertinoIcons class for iOS style icons.
cupertino_icons: ^1.0.2
dev_dependencies:
flutter_test:
sdk: flutter
# The "flutter_lints" package below contains a set of recommended lints to
# encourage good coding practices. The lint set provided by the package is
# activated in the `analysis_options.yaml` file located at the root of your
# package. See that file for information about deactivating specific lint
# rules and activating additional ones.
flutter_lints: ^1.0.0
cupertino_icons: ^1.0.2
firebase_auth: ^1.1.4
google_sign_in: ^5.0.3
font_awesome_flutter: ^9.0.0
provider: ^5.0.0
# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec
# The following section is specific to Flutter.
flutter:
# The following line ensures that the Material Icons font is
# included with your application, so that you can use the icons in
# the material Icons class.
uses-material-design: true
# To add assets to your application, add an assets section, like this:
# assets:
# - images/a_dot_burr.jpeg
# - images/a_dot_ham.jpeg
# An image asset can refer to one or more resolution-specific "variants", see
# https://flutter.dev/assets-and-images/#resolution-aware.
# For details regarding adding assets from package dependencies, see
# https://flutter.dev/assets-and-images/#from-packages
# To add custom fonts to your application, add a fonts section here,
# in this "flutter" section. Each entry in this list should have a
# "family" key with the font family name, and a "fonts" key with a
# list giving the asset and other descriptors for the font. For
# example:
# fonts:
# - family: Schyler
# fonts:
# - asset: fonts/Schyler-Regular.ttf
# - asset: fonts/Schyler-Italic.ttf
# style: italic
# - family: Trajan Pro
# fonts:
# - asset: fonts/TrajanPro.ttf
# - asset: fonts/TrajanPro_Bold.ttf
# weight: 700
#
# For details regarding fonts from package dependencies,
# see https://flutter.dev/custom-fonts/#from-packages
作为旁注：
GoogleSignInAccount? _user;
GoogleSignInAccount get user => _user!;
如果您不能 100% 确定 _user 永远不会为 null，那么这确实不是一个好的做法。但是获取 _user 可能会出错，没有返回任何值。
你的问题：
NetworkImage() 需要一个 String（不可为 null 的类型）！在您的代码 NetworkImage(user.photoURL!), 中，您通过使用 bang 运算符 (!) 告诉 dart 它在逻辑上永远不能为 null 来做到这一点。
displayName 也是如此，因为 Text() 也 requires a String 不是字符串？ --> 这就是 nullsafety 的全部要点：在 运行 时间内避免 null 错误。
解法：
确保GoogleSignInAccount? _user；在任何地方引用它之前不为空
在你的代码中。