getter 'hasFocus' 在 null 上被调用

Question

我有 8 个 TextFiled，我想为每个指定一个焦点，以便颜色发生变化。但我有一个错误 - 在 null 上调用了 getter 'hasFocus'。我该如何解决？

class _EditAccountScreenState extends State<EditAccountScreen> {
 FocusNode _focusNodeFio;
 FocusNode _focusNodeCompany;
 ...

@override
 void initState() {
   super.initState();
   _focusNodeFio = FocusNode();
   _focusNodeCompany = FocusNode();
  ...
 }

 @override
 void dispose() {
   _focusNodeFio.dispose();
   _focusNodeCompany.dispose();
 ...
   super.dispose();
 }
@override
 Widget build(BuildContext context) {
.......
Padding(
               child: TextField(
                 focusNode: _focusNodeFio,
                 onTap: () {
                   setState(() {
                     FocusScope.of(context).requestFocus(_focusNodeFio);
                   });
                 },
                 decoration: InputDecoration(
                   labelText: 'Contacts',
                   labelStyle: TextStyle(
                       color: _focusNodeFio.hasFocus ? Colors.teal[300] : Colors.grey
                   ),
                   contentPadding:

Answer 1

这行得通！

final FocusNode _fNode = FocusNode();
  
@override
Widget build(BuildContext context) {
  return Scaffold(
    body: TextField(
      focusNode: _fNode,
      onTap: () => FocusScope.of(context).requestFocus(_fNode),
      decoration: InputDecoration(
        labelText: 'Contacts',
        labelStyle: TextStyle(color: _fNode.hasFocus ? Colors.teal[300] : Colors.grey),
      ),
    ),
  );
}