我正在嘗試驗證用戶輸入的用于注冊的輸入資料并收到此錯誤[ERROR:flutter/lib/ui/ui_dart_state.cc(209)] 未處理的例外：type 'Null' 不是 type 的子型別構建背景關系'
這是我的代碼：
class _LoginState extends State<Login> {
final AuthService _auth = AuthService();
final _formKey = GlobalKey<FormState>();
TextEditingController _emailController = TextEditingController();
TextEditingController _passwordController = TextEditingController();
GoogleSignIn _googleSignIn = GoogleSignIn(scopes: ['email']);
late String _email, _password;
String error = "";
@override
void initState() {
super.initState();
}
bool _isObscure = true;
@override
Widget build(BuildContext context) {
MediaQueryData mediaQueryData = MediaQuery.of(context);
GoogleSignInAccount? user = _googleSignIn.currentUser;
final isKeyboard = MediaQuery.of(context).viewInsets.bottom != 0;
return Scaffold(
resizeToAvoidBottomInset: false,
appBar: !isKeyboard
? AppBar(
titleSpacing: 12,
leading: ModalRoute.of(context)?.canPop == true
? IconButton(
splashColor: Colors.transparent,
padding: const EdgeInsets.only(left: 30.0, bottom: 15.0),
icon: Icon(
Icons.arrow_back,
size: 35,
),
onPressed: () => Navigator.of(context).pop(),
color: Colors.black,
)
: null,
title: Image.asset('images/logo-name.png'),
backgroundColor: new Color(0xffff),
shadowColor: Colors.transparent,
elevation: 0,
toolbarHeight: 90.0,
)
: null,
body: Center(
child: Column(
children: <Widget>[
if (!isKeyboard)
Container(
child: RichText(
textAlign: TextAlign.center,
text: TextSpan(
text: "Made e-Groceries easier",
style: TextStyle(
fontSize: mediaQueryData.textScaleFactor /
mediaQueryData.textScaleFactor *
33,
fontFamily: 'Inter',
fontWeight: FontWeight.w600,
color: Colors.black)),
),
width: mediaQueryData.size.width * 0.8,
),
Container(
child: Image(
image: AssetImage("images/login.png"), fit: BoxFit.contain),
),
Container(
width: mediaQueryData.size.width * 0.85,
child: Form(
key: _formKey,
child: SingleChildScrollView(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
TextFormField(
controller: _emailController,
validator: (input) {
if (input!.isEmpty)
return 'Pleas enter a valid Email';
},
decoration: InputDecoration(
focusedErrorBorder: OutlineInputBorder(
borderSide: BorderSide(color: Colors.red),
),
errorBorder: OutlineInputBorder(
borderSide: BorderSide(color: Colors.red),
),
errorStyle: TextStyle(height: 0.4),
contentPadding:
const EdgeInsets.symmetric(vertical: 20.0),
enabledBorder: OutlineInputBorder(
borderSide:
BorderSide(color: Color(0xff2C6846))),
focusColor: Color(0xff2C6846),
focusedBorder: OutlineInputBorder(
borderSide: BorderSide(
color: Color(0xff2C6846),
)),
labelStyle: TextStyle(color: Color(0xff2C6846)),
labelText: "Email",
prefixIcon:
Icon(Icons.mail, color: Color(0xff2C6846)),
),
onSaved: (input) => _email = input!),
SizedBox(height: 20),
TextFormField(
obscureText: _isObscure,
enableSuggestions: false,
autocorrect: false,
controller: _passwordController,
validator: (input) {
if (input!.length < 6)
return 'Provide minimum 6 character';
},
decoration: InputDecoration(
focusedErrorBorder: OutlineInputBorder(
borderSide: BorderSide(color: Colors.red),
),
errorBorder: OutlineInputBorder(
borderSide: BorderSide(color: Colors.red),
),
errorStyle: TextStyle(height: 0.4),
contentPadding: const EdgeInsets.symmetric(
vertical: 20.0),
enabledBorder: OutlineInputBorder(
borderSide:
BorderSide(color: Color(0xff2C6846))),
focusColor: Color(0xff2C6846),
focusedBorder: OutlineInputBorder(
borderSide:
BorderSide(color: Color(0xff2C6846))),
labelStyle:
TextStyle(color: Color(0xff2C6846)),
labelText: "Password",
suffixIcon: IconButton(
icon: Icon(
_isObscure
? Icons.visibility
: Icons.visibility_off,
color: Color(0xff2C6846),
),
onPressed: () {
setState(() {
_isObscure = !_isObscure;
});
},
),
prefixIcon: Icon(Icons.lock,
color: Color(0xff2C6846))),
onSaved: (input) => _password = input!),
])))),
SizedBox(height: 20),
ButtonTheme(
buttonColor: Color(0xff2C6846),
minWidth: mediaQueryData.size.width * 0.85,
height: 60.0,
child: RaisedButton(
shape: RoundedRectangleBorder(
borderRadius: new BorderRadius.circular(5.0),
),
padding: EdgeInsets.fromLTRB(70, 10, 70, 10),
onPressed: () {
if (_formKey.currentState!.validate()) {
signInUser();
}
},
child: Text('Log In',
style: TextStyle(
color: Colors.white,
fontSize: 20.0,
fontWeight: FontWeight.w600))),
)
],
),
),
);
}
void signInUser() async {
dynamic authResult = await _auth.loginUser(
_emailController.text, _passwordController.text);
if (authResult == null) {
print("Sign in error. Could not be able to login");
} else {
_emailController.clear();
_passwordController.clear();
print('Sign in Successful');
Navigator.push(
context, MaterialPageRoute(builder: (context) => HomePage()));
}
}
}
上面的代碼是針對 AuthService.dart 的：
class AuthService {
final FirebaseAuth _auth = FirebaseAuth.instance;
showError(Object errormessage) {
var context;
showDialog(
context: context,
builder: (BuildContext context) {
return AlertDialog(
title: Text('Note'),
content: Text(errormessage.toString()),
actions: <Widget>[
FlatButton(
onPressed: () {
Navigator.of(context).pop();
},
child: Text('OK'))
],
);
});
}
Future loginUser(String email, String password) async {
try {
UserCredential result = await _auth.signInWithEmailAndPassword(
email: email.toString(), password: password.toString());
return result.user;
} catch (e) {
showError(e);
}
}
}
忽略凌亂的縮進，因為這是我第一次使用堆疊溢位。
uj5u.com熱心網友回復：
...
showError(Object errormessage) {
var context;
showDialog(
context: context,
...
showDialog 方法接受一個背景關系引數，它使用這個背景關系來查找有關您的應用程式的一些特殊有用的資訊，以便正確顯示對話框，但您沒有傳遞正確的背景關系。
您正在做的是首先宣告一個變數context，然后傳遞該變數，默認情況下該變數的值為 null，因此您會收到錯誤訊息。
要解決此問題，您需要傳遞應用程式使用的真實背景關系：
...
showError(BuildContext context, Object errormessage) {
showDialog(
context: context,
...
接著：
Future loginUser(BuildContext context, String email, String password) async {
try {
UserCredential result = await _auth.signInWithEmailAndPassword(
email: email.toString(), password: password.toString());
return result.user;
} catch (e) {
showError(context, e);
}
}
最后：
...
void signInUser() async {
dynamic authResult = await _auth.loginUser(context, _emailController.text, _passwordController.text);
...
uj5u.com熱心網友回復：
問題可能來自
Navigator.push(
context, MaterialPageRoute(builder: (context) => HomePage()));
所以創建全域 BuildContext 變數并從 build 方法初始化它。或者發送背景關系作為引數。喜歡
signInUser(BuildContext context)
uj5u.com熱心網友回復：
'Null' 不是型別 'BuildContext' 錯誤的子型別意味著代碼需要你 BuildContext 但可能你給了 null。因此，您應該使用部件檢查 BuildContext。當我查看您的代碼時，我看到了錯誤行。錯誤是您定義了背景關系而不是設定任何內容。所以它的值為空。您應該通過引數傳遞背景關系。如果您通過背景關系，您的問題將得到解決。
showError(Object errormessage) {
var context;
showDialog(
context: context,
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