Error: Null safety features are disabled for this library in Flutter
Error: Null safety features are disabled for this library in Flutter
我也在 pubspec 中添加了 non-nullabe。我不想更改我的 SDK 版本，因为我已经将它用于其他依赖项，如果我更改版本会导致错误。请让我知道如何删除此错误。请告诉我如何解决这个问题，因为我是 Flutter 的新手
错误：
lib/BluetoothScanningDevices.dart:113:40: Error: Null safety features are disabled for this library.
Try removing the package language version or setting the language version to 2.12 or higher.
children: snapshot.data!
^
我的 pubspec.yaml 文件如下所示：
name: epicare
description: Epilepsy monitoring application.
# The following line prevents the package from being accidentally published to
# pub.dev using `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: ">=2.7.0 <3.0.0"
analyzer:
enable-experiment:
- non-nullable
dependencies:
table_calendar: ^2.2.1
shared_preferences: ^0.5.4+5
permission_handler: ^5.0.0
contacts_service: ^0.3.10
url_launcher: ^5.4.2
flutter_switch: ^0.2.2
flutter:
sdk: flutter
custom_switch: ^0.0.1
charts_flutter: ^0.10.0
image_picker: ^0.6.7+22
loading_animations: ^2.1.0
flutter_spinkit: ^4.1.2
cupertino_icons: ^0.1.3
flutter_launcher_icons: ^0.9.0
flutter_local_notifications: ^1.4.4+2
focused_menu: ^1.0.0
fluttertoast: ^4.0.0
contact_picker: ^0.0.2
google_sign_in: ^3.3.0
http: ^0.12.0+4
provider: ^5.0.0
firebase_core: ^0.5.0
firebase_auth: ^0.18.0+1
flutter_blue: ^0.8.0
bluetooth_enable: ^0.1.1
flutter_bluetooth_serial: ^0.2.2
dev_dependencies:
flutter_test:
sdk: flutter
使用蓝牙功能的代码：
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'BluetoothConnectBand.dart';
import 'BluetoothConnectedSuccess.dart';
import 'package:flutter_blue/flutter_blue.dart';
class BluetoothScanningDevices extends StatefulWidget {
@override
_BluetoothScanningDevicesState createState() =>
_BluetoothScanningDevicesState();
}
class _BluetoothScanningDevicesState extends State<BluetoothScanningDevices> {
FlutterBlue flutterBlue = FlutterBlue.instance;
@override
Widget build(BuildContext context) {
Size size = MediaQuery.of(context).size;
return Scaffold(
appBar: AppBar(
backgroundColor: const Color(0xffE5E0A1),
elevation: 0,
centerTitle: true,
title: Text(
"Connect Band",
style: TextStyle(
fontSize: 15.0,
color: Colors.black,
fontFamily: 'Montserrat',
fontWeight: FontWeight.normal,
),
),
leading: IconButton(
icon: Icon(
Icons.arrow_back,
color: Colors.black,
),
onPressed: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) {
return BluetoothConnectBand();
},
),
);
},
),
actions: [
Padding(
padding: EdgeInsets.only(right: 5.0),
child: FlatButton(
onPressed: () {},
child: Text(
"Search",
style: TextStyle(
fontSize: 15.0,
color: Colors.black,
fontWeight: FontWeight.normal,
fontFamily: 'Montserrat',
),
),
),
)
],
),
body: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Container(
height: size.height * 0.4,
width: size.width,
color: const Color(0xffE5E0A1),
child: Image.asset(
'assets/images/bluetooth.png',
)),
Container(
width: size.width,
padding: EdgeInsets.symmetric(vertical: 20),
child: Text(
"Scanning Available Devices...",
style: TextStyle(
fontSize: 15.0,
color: Colors.black,
fontWeight: FontWeight.w400,
fontFamily: 'Montserrat',
),
textAlign: TextAlign.center,
),
),
StreamBuilder<List<BluetoothDevice>>(
stream: Stream.periodic(Duration(seconds: 2))
.asyncMap((_) => FlutterBlue.instance.connectedDevices),
initialData: [],
builder: (c, snapshot) => Column(
children: snapshot.data!
.map((d) => ListTile(
title: Text(d.name),
subtitle: Text(d.id.toString()),
trailing: StreamBuilder<BluetoothDeviceState>(
stream: d.state,
initialData: BluetoothDeviceState.disconnected,
builder: (c, snapshot) {
if (snapshot.data ==
BluetoothDeviceState.connected) {
return RaisedButton(
child: Text('OPEN'),
onPressed: (){}
);
}
return Text(snapshot.data.toString());
},
),
))
.toList(),
),
),
],
),
);
}
}
有 种方法可以在遗留代码中使用不可为 null 的包，但它们需要使用 --no-sound-null-safety 调用各种命令。更好的做法是按照 https://dart.dev/null-safety/migration-guide.
中所示的步骤迁移您的代码
在空安全世界中，我们使用“！”表明变量不能为空，但为了使用这些很酷的特性，dart SDK 版本应该大于 2.12。
报错信息清楚的写明了问题所在的行号，不用改版本也不用迁移，去掉“！”在 BluetoothScanningDevices.dart 文件中的第 113 行 snapshot.data 之后。
我在必须进行更改的代码片段中添加了注释。
builder: (c, snapshot) => Column(
// Important: remove the exclamation after snapshot.data to fix the error.
children: snapshot.data!
.map((d) => ListTile(
title: Text(d.name),
subtitle: Text(d.id.toString()),
trailing: StreamBuilder<BluetoothDeviceState>(
stream: d.state,
initialData: BluetoothDeviceState.disconnected,
builder: (c, snapshot) {
if (snapshot.data ==
BluetoothDeviceState.connected) {
return RaisedButton(
child: Text('OPEN'),
onPressed: (){}
);
}
return Text(snapshot.data.toString());
},
),
))
如何使用不同版本的同一个包
像这样使用->（环境上面的分析器）
version: 1.0.6+13
analyzer:
enable-experiment:
- non-nullable
environment:
sdk: ">=2.7.0 <3.0.0"
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
flutter_bloc: ^6.1.1
bloc_provider: ^0.7.0+3
provider: ^4.3.2+3
shared_preferences: ^0.5.12+4
package_info: ^2.0.0
#firebase
firebase_core: ^1.1.0
firebase_analytics: ^8.0.2
firebase: ^9.0.1
firebase_crashlytics: ^2.0.2
dependency_overrides:
firebase_core_platform_interface: ^4.0.0
plugin_platform_interface: ^2.0.0
http: ^0.13.0
http_parser: ^4.0.0
shared_preferences: ^2.0.5
path_provider_windows: ^2.0.0
path_provider_platform_interface: ^2.0.0
path_provider_linux: ^2.0.0
dev_dependencies:
flutter_test:
sdk: flutter
我也在 pubspec 中添加了 non-nullabe。我不想更改我的 SDK 版本，因为我已经将它用于其他依赖项，如果我更改版本会导致错误。请让我知道如何删除此错误。请告诉我如何解决这个问题，因为我是 Flutter 的新手
错误：
lib/BluetoothScanningDevices.dart:113:40: Error: Null safety features are disabled for this library.
Try removing the package language version or setting the language version to 2.12 or higher.
children: snapshot.data!
^
我的 pubspec.yaml 文件如下所示：
name: epicare
description: Epilepsy monitoring application.
# The following line prevents the package from being accidentally published to
# pub.dev using `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: ">=2.7.0 <3.0.0"
analyzer:
enable-experiment:
- non-nullable
dependencies:
table_calendar: ^2.2.1
shared_preferences: ^0.5.4+5
permission_handler: ^5.0.0
contacts_service: ^0.3.10
url_launcher: ^5.4.2
flutter_switch: ^0.2.2
flutter:
sdk: flutter
custom_switch: ^0.0.1
charts_flutter: ^0.10.0
image_picker: ^0.6.7+22
loading_animations: ^2.1.0
flutter_spinkit: ^4.1.2
cupertino_icons: ^0.1.3
flutter_launcher_icons: ^0.9.0
flutter_local_notifications: ^1.4.4+2
focused_menu: ^1.0.0
fluttertoast: ^4.0.0
contact_picker: ^0.0.2
google_sign_in: ^3.3.0
http: ^0.12.0+4
provider: ^5.0.0
firebase_core: ^0.5.0
firebase_auth: ^0.18.0+1
flutter_blue: ^0.8.0
bluetooth_enable: ^0.1.1
flutter_bluetooth_serial: ^0.2.2
dev_dependencies:
flutter_test:
sdk: flutter
使用蓝牙功能的代码：
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'BluetoothConnectBand.dart';
import 'BluetoothConnectedSuccess.dart';
import 'package:flutter_blue/flutter_blue.dart';
class BluetoothScanningDevices extends StatefulWidget {
@override
_BluetoothScanningDevicesState createState() =>
_BluetoothScanningDevicesState();
}
class _BluetoothScanningDevicesState extends State<BluetoothScanningDevices> {
FlutterBlue flutterBlue = FlutterBlue.instance;
@override
Widget build(BuildContext context) {
Size size = MediaQuery.of(context).size;
return Scaffold(
appBar: AppBar(
backgroundColor: const Color(0xffE5E0A1),
elevation: 0,
centerTitle: true,
title: Text(
"Connect Band",
style: TextStyle(
fontSize: 15.0,
color: Colors.black,
fontFamily: 'Montserrat',
fontWeight: FontWeight.normal,
),
),
leading: IconButton(
icon: Icon(
Icons.arrow_back,
color: Colors.black,
),
onPressed: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) {
return BluetoothConnectBand();
},
),
);
},
),
actions: [
Padding(
padding: EdgeInsets.only(right: 5.0),
child: FlatButton(
onPressed: () {},
child: Text(
"Search",
style: TextStyle(
fontSize: 15.0,
color: Colors.black,
fontWeight: FontWeight.normal,
fontFamily: 'Montserrat',
),
),
),
)
],
),
body: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Container(
height: size.height * 0.4,
width: size.width,
color: const Color(0xffE5E0A1),
child: Image.asset(
'assets/images/bluetooth.png',
)),
Container(
width: size.width,
padding: EdgeInsets.symmetric(vertical: 20),
child: Text(
"Scanning Available Devices...",
style: TextStyle(
fontSize: 15.0,
color: Colors.black,
fontWeight: FontWeight.w400,
fontFamily: 'Montserrat',
),
textAlign: TextAlign.center,
),
),
StreamBuilder<List<BluetoothDevice>>(
stream: Stream.periodic(Duration(seconds: 2))
.asyncMap((_) => FlutterBlue.instance.connectedDevices),
initialData: [],
builder: (c, snapshot) => Column(
children: snapshot.data!
.map((d) => ListTile(
title: Text(d.name),
subtitle: Text(d.id.toString()),
trailing: StreamBuilder<BluetoothDeviceState>(
stream: d.state,
initialData: BluetoothDeviceState.disconnected,
builder: (c, snapshot) {
if (snapshot.data ==
BluetoothDeviceState.connected) {
return RaisedButton(
child: Text('OPEN'),
onPressed: (){}
);
}
return Text(snapshot.data.toString());
},
),
))
.toList(),
),
),
],
),
);
}
}
有 种方法可以在遗留代码中使用不可为 null 的包，但它们需要使用 --no-sound-null-safety 调用各种命令。更好的做法是按照 https://dart.dev/null-safety/migration-guide.
在空安全世界中，我们使用“！”表明变量不能为空，但为了使用这些很酷的特性，dart SDK 版本应该大于 2.12。
报错信息清楚的写明了问题所在的行号，不用改版本也不用迁移，去掉“！”在 BluetoothScanningDevices.dart 文件中的第 113 行 snapshot.data 之后。
我在必须进行更改的代码片段中添加了注释。
builder: (c, snapshot) => Column(
// Important: remove the exclamation after snapshot.data to fix the error.
children: snapshot.data!
.map((d) => ListTile(
title: Text(d.name),
subtitle: Text(d.id.toString()),
trailing: StreamBuilder<BluetoothDeviceState>(
stream: d.state,
initialData: BluetoothDeviceState.disconnected,
builder: (c, snapshot) {
if (snapshot.data ==
BluetoothDeviceState.connected) {
return RaisedButton(
child: Text('OPEN'),
onPressed: (){}
);
}
return Text(snapshot.data.toString());
},
),
))
如何使用不同版本的同一个包 像这样使用->（环境上面的分析器）
version: 1.0.6+13
analyzer:
enable-experiment:
- non-nullable
environment:
sdk: ">=2.7.0 <3.0.0"
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
flutter_bloc: ^6.1.1
bloc_provider: ^0.7.0+3
provider: ^4.3.2+3
shared_preferences: ^0.5.12+4
package_info: ^2.0.0
#firebase
firebase_core: ^1.1.0
firebase_analytics: ^8.0.2
firebase: ^9.0.1
firebase_crashlytics: ^2.0.2
dependency_overrides:
firebase_core_platform_interface: ^4.0.0
plugin_platform_interface: ^2.0.0
http: ^0.13.0
http_parser: ^4.0.0
shared_preferences: ^2.0.5
path_provider_windows: ^2.0.0
path_provider_platform_interface: ^2.0.0
path_provider_linux: ^2.0.0
dev_dependencies:
flutter_test:
sdk: flutter