错误：空检查操作员在零值上使用 - 用于布尔值 -
https：//flutterigniter.com/checking-null-aware-aware-aware-aware-operators-dart/ /a>
null check ock ock ock operator in null value
值可以为null，然后我们可以使用??操作员为其分配一个值。我尝试过，它仍然显示出相同的错误：
这是数据结构。
main.dart
import 'package:flutter/material.dart';
import 'dart:convert';
BigData bigDataFromJson(String str) => BigData.fromJson(json.decode(str));
class BigData {
BigData({
this.data,
});
Data? data;
factory BigData.fromJson(Map<String, dynamic> json) => BigData(
data: Data.fromJson(json["data"]),
);
Map<String, dynamic> toJson() => {
"data": data!.toJson(),
};
}
class Data {
Data({
this.lockoutDetails,
});
bool? lockoutDetails;
factory Data.fromJson(Map<String, dynamic> json) => Data(
lockoutDetails: json["lockout_details"],
);
Map<String, dynamic> toJson() => {
"lockout_details": lockoutDetails,
};
}
此处从拖放的默认应用程序开始：
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
@override
State<MyHomePage> createState() => _MyHomePageState();
}
在这里，我从上面的数据架构中使用了变量lockoutdetails，它显示了使用的错误null检查操作员零值。
class _MyHomePageState extends State<MyHomePage> {
BigData d = BigData();
@override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child:
d.data!.lockoutDetails ?? true
? const Text(
'AAA',
)
: Container(),
));
}
}
纠正它的方法是什么？
https://flutterigniter.com/checking-null-aware-operators-dart/
Null check operator used on a null value
These links say that if the value can be null then we can use ?? operator to assign a value to it. I tried it, it still shows the same error:
This is the data structure.
main.dart
import 'package:flutter/material.dart';
import 'dart:convert';
BigData bigDataFromJson(String str) => BigData.fromJson(json.decode(str));
class BigData {
BigData({
this.data,
});
Data? data;
factory BigData.fromJson(Map<String, dynamic> json) => BigData(
data: Data.fromJson(json["data"]),
);
Map<String, dynamic> toJson() => {
"data": data!.toJson(),
};
}
class Data {
Data({
this.lockoutDetails,
});
bool? lockoutDetails;
factory Data.fromJson(Map<String, dynamic> json) => Data(
lockoutDetails: json["lockout_details"],
);
Map<String, dynamic> toJson() => {
"lockout_details": lockoutDetails,
};
}
Here from the default application of Flutter starts:
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
@override
State<MyHomePage> createState() => _MyHomePageState();
}
Here I have used the variable lockoutDetails from the above datastructures and it shows the error null check operator used on a null value.
class _MyHomePageState extends State<MyHomePage> {
BigData d = BigData();
@override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child:
d.data!.lockoutDetails ?? true
? const Text(
'AAA',
)
: Container(),
));
}
}
What is the way to correct it?
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评论（3）
你可以使用吗？而不是！这意味着它可能或可能无效。如果添加！您提到它不是零，但值是未知的
you can use ? instead of ! which means that it may or maynot be null. If you add ! you are mentioning that its not null but the value is unknown
d.data在这种情况下是无效的，您可以替换为
d.datais null in this case, you can replacewith
您的
d.data为空。为了进行测试，请使用
d.data?.lockoutdetails。考虑设置数据以具有价值。
Your
d.datais null.For test run use
d.data?.lockoutDetails.Think to set data for to have value.