flutter - Flutter 中 TextField 小部件的 prefixIcon 在聚焦 TextField 时消失。怎么解决？

Question

只是在探索 flutter 并卡住了。 prefixIcon 在单击字段时消失，聚焦时又出现。如何解决这个问题？代码如下。尝试删除表单的 key 。我希望图标在聚焦或聚焦时保持不变。还有其他属性要设置吗？找不到修复程序。

        class _MyHomePageState extends State<MyHomePage> {
          String _email = "";
          String _password = "";

          final  _formKey = GlobalKey<FormState>();
          final FocusNode _emailFocus = FocusNode();
          final FocusNode _passwordFocus = FocusNode();



          @override
          Widget build(BuildContext context) {
            return Scaffold(
              appBar: AppBar(
                title: Text(widget.title),
              ),
              body: Container(
                      padding: const EdgeInsets.symmetric(horizontal: 50.0,vertical: 100.0),
                      decoration: BoxDecoration(color: Colors.white),
                      child:Form(
                        key: _formKey,
                        child: Column(
                          crossAxisAlignment: CrossAxisAlignment.start,
                          children: <Widget>[
                            TextFormField(
                              focusNode: _emailFocus,
                                decoration: InputDecoration(
                                    labelText: 'Username or email',
                                    prefixIcon: Icon(Icons.person), //prefixIcon
                                  focusedBorder: UnderlineInputBorder(),
                                  hintText: "example@mail.com",
                                )
                            ),
                            Padding(
                              padding: const EdgeInsets.symmetric(vertical: 16.0),
                            ),
                              TextFormField(
                              obscureText: true,
                              focusNode: _passwordFocus,
                                  decoration: InputDecoration(
                                    labelText: 'Password',
                                    prefixIcon: Icon(Icons.lock),
                                    focusedBorder: UnderlineInputBorder(),
                                  )
                            ) ,
                            Padding(
                              padding: const EdgeInsets.symmetric(vertical: 16.0),
                              child: RaisedButton(
                                onPressed: () {
                                  // Validate will return true if the form is valid, or false if
                                  // the form is invalid.
                                  if (_formKey.currentState.validate()) {
                                    // Process data.
                                  }
                                },
                                child: Text('Submit'),
                              ),
                            ),
                          ],
                        ),
                      )
              )
            );
          }
        }

Answer 1

问题是我将原色设置为白色。因此，只要聚焦场，它就会消失，因为背景也是白色的。我的错。