如何解决错误:Null检查操作符用于空值?

Question

字段验证无效，显示错误:Null检查操作符用于空值。我以doc .flutter为例。我怎么解决这个问题?

class _AddGroupPageState extends State<AddGroupPage> {
final _groupController = TextEditingController();
final _formKey = GlobalKey<FormState>();
@override
void dispose() {
_groupController.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return: Scaffold(
body: Padding(
padding: const EdgeInsets.all(8.0),
child: Column(
children: [
TextFormField(
key: _formKey,
controller: _groupController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Group name cannot be empty';
}
return null;
},
),
],
),
),
...

void _saveGroup() {
final isValid = _formKey.currentState!.validate();
if (isValid) {
BlocProvider.of<NewGroupBloc>(context)
.add(AddGroupEvent(_groupController.text.trim()));
}
}

Answer 1

用Form小部件包装TextFormField并将formkey传递给该小部件

Form(
key: _formKey,
child: TextFormField(
controller: _groupController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Group name cannot be empty';
}
return null;
},
),
),

Answer 2

你必须给formKey表单而不是textfield本身像这样使用:

Form(
key: _formKey,
child: Column(
children: [
TextFormField(

//your code