Question

我真的是用flutter新建的，我试图用带有登录和注册标签的标签栏构建登录页面。在具有使用2个小部件作为子项的标签栏im的LoginPage中，问题是当我尝试仅使用Login小部件登录时它完全正常且可以正常工作，但是当我在标签条中使用im时我总是会收到错误消息，登录窗口小部件中的文本字段始终返回null值，发生什么情况

im使用md2_tab_indicator版本1.0.2

这是登录页面：

    class AuthScreen extends StatefulWidget {
  @override
  _AuthScreenState createState() => _AuthScreenState();
}

class _AuthScreenState extends State<AuthScreen> {
  @override
  Widget build(BuildContext context) {
    UIHelper.init(context);
    return Scaffold(
      body: SafeArea(
        child: DefaultTabController(
            length: 2,
            child: Container(
              color: Colors.orange[50],
              child: ListView(
                shrinkWrap: true,
                children: <Widget>[
                  Container(
                    padding: EdgeInsets.only(
                        right: 20.0, left: 20.0, top: 100.0, bottom: 20.0),
                    child: Image(
                      image: AssetImage('images/fare.gi.png'),
                      height: 150.0,
                    ),
                  ),
                  Center(
                    child: TabBar(
                      labelStyle: TextStyle(
                          //up to your taste
                          fontSize: 18,
                          fontWeight: FontWeight.w700),
                      indicatorSize:
                          TabBarIndicatorSize.label, 
                      labelColor: Colors.red[400], 
                      unselectedLabelColor: Color(0xff5f6368), 
                      isScrollable: true, //up to your taste
                      indicator: MD2Indicator(
                          //it begins here
                          indicatorHeight: 3,
                          indicatorColor: Colors.red[400],
                          indicatorSize: MD2IndicatorSize
                              .full //3 different modes tiny-normal-full
                          ),
                      tabs: <Widget>[
                        Tab(
                          text: "Login",
                        ),
                        Tab(
                          text: "Register",
                        ),
                      ],
                    ),
                  ),
                  SizedBox(
                    height: 40,
                  ),
                  Container(
                    height: MediaQuery.of(context).size.height,
                    child: TabBarView(
                      children: <Widget>[LoginScreen(), RegisterScreen()],
                    ),
                  )
                ],
              ),
            )),
      ),
    );
  }
}

这是登录小部件

    class LoginScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    bool _isLoading = false;
    Api api = Api();
    String email;
    String password;
    return Material(
      child: Container(
        decoration: BoxDecoration(
          gradient: LinearGradient(
              colors: [Colors.orange[50], Colors.red[400]],
              begin: Alignment.topCenter,
              end: Alignment.bottomCenter),
        ),
        child: _isLoading
            ? Center(child: CircularProgressIndicator())
            : ListView(
                children: <Widget>[
                  Container(
                    width: MediaQuery.of(context).size.width,
                    padding: EdgeInsets.symmetric(horizontal: 60.0),
                    child: Column(
                      children: <Widget>[
                        FloatingInputBox(
                          'Email',
                          onChanged: (value) => email = value,
                        ),
                        SizedBox(
                          height: 20.0,
                        ),
                        FloatingInputBox(
                          'Password',
                          onChanged: (value) => password = value,
                          obscureText: true,
                        ),
                      ],
                    ),
                  ),
                  ButtonSection(
                      label: 'Login',
                      onPressed: () async {
                        print('username: $email');
                        print('password: $password');
                        Result result = await api.login(email, password);
                        if (result.resultType == ResultType.Success)
                          Navigator.push(context,
                              MaterialPageRoute(builder: (_) => Home()));
                      }),
                ],
              ),
      ),
    );
  }
}

Answer 1

原因是您将变量放在Widget build下，当Widget build时，所有变量都将重置
来自

Widget build(BuildContext context) {
    bool _isLoading = false;
    Api api = Api();
    String email;
    String password;

到

bool _isLoading = false;
Api api = Api();
String email;
String password;

Widget build(BuildContext context) {

当使用标签栏的脚手架上使用的小部件

1 个答案: