颤振错误 - 断言失败：第 298 行 pos 10："data ！= null"：必须向文本小部件提供非空字符串。登录时

Question

我一直在一个使用rest api登录和注销的小项目中工作。但每当我尝试登录时，我都会收到错误

[ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: 'package:flutter/src/widgets/text.dart': Failed assertion: line 298 pos 10: 'data != null': A non-null String must be provided to a Text widget.

出于测试目的，我的密码是12345，但当我将密码更改为仅字符串示例abcd时，当我将口令更改为字符串和数字混合时，会产生相同的错误。这是flutter登录页面的代码，谢谢。

class LogIn extends StatefulWidget {
@override
_LogInState createState() => _LogInState();
}
class _LogInState extends State<LogIn> {
bool _isLoading = false;
TextEditingController mailController = TextEditingController();
TextEditingController passwordController = TextEditingController();
ScaffoldState scaffoldState;
_showMsg(msg) { //
final snackBar = SnackBar(
content: Text(msg),
action: SnackBarAction(
label: 'Close',
onPressed: () {
// Some code to undo the change!
},
),
);
Scaffold.of(context).showSnackBar(snackBar);
}
@override
Widget build(BuildContext context) {
return Scaffold(
resizeToAvoidBottomInset : false,
body: Container(
child: Stack(
children: <Widget>[
///////////  background///////////
new Container(
decoration: new BoxDecoration(
gradient: LinearGradient(
begin: Alignment.topLeft,
end: Alignment.bottomRight,
stops: [0.0, 0.4, 0.9],
colors: [
Color(0xFFFF835F),
Color(0xFFFC663C),
Color(0xFFFF3F1A),
],
),
),
),
Positioned(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Card(
elevation: 4.0,
color: Colors.white,
margin: EdgeInsets.only(left: 20, right: 20),
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(15)),
child: Padding(
padding: const EdgeInsets.all(10.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
/////////////  Email//////////////
TextField(
style: TextStyle(color: Color(0xFF000000)),
controller: mailController,
cursorColor: Color(0xFF9b9b9b),
keyboardType: TextInputType.text,
decoration: InputDecoration(
prefixIcon: Icon(
Icons.account_circle,
color: Colors.grey,
),
hintText: "Email",
hintStyle: TextStyle(
color: Color(0xFF9b9b9b),
fontSize: 15,
fontWeight: FontWeight.normal),
),
),
/////////////// password////////////////////
///passwordController
TextField(
style: TextStyle(color: Color(0xFF000000)),
cursorColor: Color(0xFF9b9b9b),
controller: passwordController,
obscureText: true,
decoration: InputDecoration(
prefixIcon: Icon(
Icons.vpn_key,
color: Colors.grey,
),
hintText: "Password",
hintStyle: TextStyle(
color: Color(0xFF9b9b9b),
fontSize: 15,
fontWeight: FontWeight.normal),
),
),

/*TextFormField(
controller: passwordController,
cursorColor: Colors.white,
obscureText: true,
style: TextStyle(color: Colors.white70),
decoration: InputDecoration(
icon: Icon(Icons.lock, color: Colors.white70),
hintText: "Password",
border: UnderlineInputBorder(borderSide: BorderSide(color: Colors.white70)),
hintStyle: TextStyle(color: Colors.white70),
),
),*/
/////////////  LogIn Botton///////////////////
Padding(
padding: const EdgeInsets.all(10.0),
child: FlatButton(
child: Padding(
padding: EdgeInsets.only(
top: 8, bottom: 8, left: 10, right: 10),
child: Text(
_isLoading? 'Loging...' : 'Login',
textDirection: TextDirection.ltr,
style: TextStyle(
color: Colors.white,
fontSize: 15.0,
decoration: TextDecoration.none,
fontWeight: FontWeight.normal,
),
),
),
color: Color(0xFFFF835F),
disabledColor: Colors.grey,
shape: new RoundedRectangleBorder(
borderRadius:
new BorderRadius.circular(20.0)),
onPressed: _isLoading ? null : _login,
),
),
],
),
),
),
////////////   new account///////////////
Padding(
padding: const EdgeInsets.only(top: 20),
child: InkWell(
onTap: () {
Navigator.push(
context,
new MaterialPageRoute(
builder: (context) => SignUp()));
},
child: Text(
'Create new Account',
textDirection: TextDirection.ltr,
style: TextStyle(
color: Colors.white,
fontSize: 15.0,
decoration: TextDecoration.none,
fontWeight: FontWeight.normal,
),
),
),
),
],
),
),
)
],
),
),
);
}
void _login() async{
setState(() {
_isLoading = true;
});

var data = {
'email' : mailController.text,
'password' : passwordController.text
};
var res = await CallApi().postData(data, 'login');
var body = json.decode(res.body);
if(body['message']==true){ // success to messsage
//  _showMsg(body['message']);
print(body['accessToken']); // from token to accessToken
/*SharedPreferences localStorage = await SharedPreferences.getInstance();
localStorage.setString('token', body['token']);
localStorage.setString('user', json.encode(body['user']));*/
Navigator.push(
context,
new MaterialPageRoute(
builder: (context) => Home()));
}else{
_showMsg(body['message']);
}

setState(() {
_isLoading = false;
});

}
}

Answer 1

感谢所有试图提供帮助的人。我发现解决方案不是来自文本，而是来自服务器的响应不是json格式的，它只是一个响应。我的错误来自这里

return response([
'success' => true,
'token' =>$token,
'user' =>$user,
'message'=>'Successfully Logged In'
]);

解决方案是消息。字符串

return response()->json([
'success' => true,
'token' =>$token,
'user' =>$user,
'message'=>'Successfully Logged In'
]);

如果有人遇到问题并且不清楚，你可以问我。