Flutter 中的 Dart Futures 问题:断言失败:第 146 行:'<optimized out>': is not true
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【中文标题】Flutter 中的 Dart Futures 问题:断言失败:第 146 行:\'<optimized out>\': is not true【英文标题】:Trouble with Dart Futures in Flutter : Failed assertion: line 146: '<optimized out>': is not trueFlutter 中的 Dart Futures 问题:断言失败:第 146 行:'<optimized out>': is not true 【发布时间】:2019-04-11 14:17:37 【问题描述】:我正在为我的应用程序构建一个用户身份验证模块,但我遇到了一些异步代码的问题。
首先,这是抛出的错误:
E/flutter (17162): [ERROR:flutter/shell/common/shell.cc(188)] Dart 错误:未处理的异常: E/flutter(17162):“dart:async/future_impl.dart”:断言失败:第 146 行:“优化”:不正确。 E/flutter (17162): #0 _AssertionError._doThrowNew (dart:core/runtime/liberrors_patch.dart:40:39) E/flutter (17162): #1 _AssertionError._throwNew (dart:core/runtime/liberrors_patch.dart:36:5) E/flutter (17162): #2 _FutureListener.handleError (dart:async/future_impl.dart:146:14) E/flutter (17162): #3 Future._propagateToListeners.handleError (dart:async/future_impl.dart:654:47) E/flutter (17162): #4 Future._propagateToListeners (dart:async/future_impl.dart:675:24) E/flutter (17162): #5 Future._completeError (dart:async/future_impl.dart:494:5) E/flutter (17162): #6 _SyncCompleter._completeError (dart:async/future_impl.dart:55:12) E/flutter (17162): #7 _Completer.completeError (dart:async/future_impl.dart:27:5) E/flutter (17162): #8 _AsyncAwaitCompleter.completeError (dart:async/runtime/libasync_patch.dart:40:18) E/flutter (17162):#9 FirebaseAuth.signInWithEmailAndPassword(包:firebase_auth/firebase_auth.dart) E/颤振(17162): E/flutter (17162):#10 Session.login。 (包:mood_map/utilities/session.dart:31:24) E/flutter (17162): #11 _RootZone.runUnary (dart:async/zone.dart:1379:54) E/flutter (17162): #12 _FutureListener.handleValue (dart:async/future_impl.dart:129:18) E/flutter (17162): #13 Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:642:45) E/flutter (17162): #14 Future._propagateToListeners (dart:async/future_impl.dart:671:32) E/flutter (17162): #15 Future._complete (dart:async/future_impl.dart:476:7) E/flutter (17162): #16 _SyncCompleter.complete (dart:async/future_impl.dart:51:12) E/flutter (17162): #17 _AsyncAwaitCompleter.complete (dart:async/runtime/libasync_patch.dart:28:18) E/flutter (17162): #18 _completeOnAsyncReturn (dart:async/runtime/libasync_patch.dart:295:13) E/flutter (17162): #19 Session._checkUserAlreadyExists (package:mood_map/utilities/session.dart) E/颤振(17162): E/flutter (17162): #20 Session.login (package:mood_map/utilities/session.dart:27:11)
这里是涉及的功能:
static final FirebaseAuth _authenticator = FirebaseAuth.instance;
static void login(BuildContext context, String email, String password) async
email = email.trim();
password = password.trim();
//Check if the user already exists
await _checkUserAlreadyExists(email).then((exists)
if(exists)
_authenticator.signInWithEmailAndPassword(email: email, password: password)
.then((FirebaseUser user) _loginSuccess(); )
.catchError((Error e) _loginFailure(context); );
else
Utilities.showMessageDialog(context, "That user doesn't exist. Please create an account below.");
);
----------------------------------------------------------------------
static Future createUserAccount(BuildContext context, email, String password) async
//Check if the user already exists
await _checkUserAlreadyExists(email).then((exists)
if(exists)
Utilities.showMessageDialog(context, "That user already exists. Please login or select another account.");
AppNavigator.navigateToLoginScreen();
else
_authenticator.createUserWithEmailAndPassword(email: email, password: password)
.then((FirebaseUser user) _createUserSuccess(); )
.catchError((Error e) _createUserFailure(context); );
);
简而言之,对 _authenticator.signonWithEmailAndPassword() 的调用失败。我知道 _authenticator 实例正在使用其他函数,所以我知道这不是 Firebase 本身的问题。
我担心我从另一个异步函数 _checkIfUserAlreadyExists() 中调用另一个异步函数 _authenticator.signonWithEmailAndPassword() 做错了事。从我读过的内容来看,这似乎可以在 .then() 块中执行,但错误消息似乎非常坚持认为这与函数调用的异步性质的设置有关。
想法?
【问题讨论】:
上述问题你得到解决方案了吗? 没有。我做了更多的研究,这似乎是当前版本的 Flutter 的系统性问题。我发现了一个报告它的 github 问题,以便开发人员知道。我也发布了我的发现。见:github.com/flutter/flutter/issues/23512 【参考方案1】:如果您使用.then()
子句,请不要使用await
。
.then()
和await
是处理Future
的两种不同方式,但不应用于相同的Future
实例。
【讨论】:
【参考方案2】:考虑使用 async - await 来捕获“最后一步”中的错误。这个回答https://github.com/flutter/flutter/issues/22734对我帮助很大。
以下是我从一个我不记得的来源获得的代码 sn-p,但它帮助我了解了如何正确使用 Futures。我对其进行了一些修改以测试我的确切情况(添加了 main4() 和 divideFullAsyncNested() 函数)。希望对你有帮助。
// SO 29378453
import 'dart:async';
import 'package:login_app/constants.dart';
main()
// fails
main1();
main2();
main3();
main4();
Future<double> divide(int a, b)
// this part is still sync
if (b == 0)
throw new Exception('Division by zero divide non-async');
// here starts the async part
return new Future.value(a / b);
Future<double> divideFullAsync(int a, b)
return new Future(()
if (b == 0)
throw new Exception('Division by zero full async');
return new Future.value(a / b);
// or just
// return a / b;
);
Future<double> divideFullAsyncNested()
return divideFullAsync(7, 8).then(
(val)
return divideFullAsync(5, 0).then(
(val2)
return Future(()
if (val2 == 1)
throw Exception('Innermost: Result not accepted exception.');
return val2;
);
,
).catchError((err) => throw Exception('Inner: $err'));
,
).catchError((err) => throw Exception('Outter: $err'));
//Future<double> divideFullAsyncNested()
// return divideFullAsync(9, 9).then(
// (val)
// return Future(
// ()
// if (val == 1)
// throw Exception('Result not accepted exception.');
//
// return val;
// ,
// );
// ,
// ).catchError((err) => throw Exception(err.toString()));
//
// async error handling doesn't catch sync exceptions
void main1() async
try
// divide(1, 0).then((result) => print('(1) 1 / 0 = $result')).catchError(
// (error) => print('(1)Error occured during division: $error'));
var result = await divide(1, 0);
print('(1) 1 / 0 = $result');
catch (ex)
print('(1.1)Error occured during division: $ex.toString()');
// async error handling catches async exceptions
void main2()
divideFullAsync(1, 0)
.then((result) => print('(2) 1 / 0 = $result'))
.catchError(
(error) => print('(2) Error occured during division: $error'));
// async/await allows to use try/catch for async exceptions
main3() async
try
await divideFullAsync(1, 0);
print('3');
catch (error)
print('(3) Error occured during division: $error');
main4() async
// try
// await divideFullAsyncNested();
// on Exception catch (e)
// print("(4) $e.toString().replaceAll('Exception:', '').trimLeft().trimRight()");
//
try
divideFullAsyncNested()
.then((v) => print(v))
.catchError((err) => print(Constants.refinedExceptionMessage(err)));
on Exception catch (e)
print("(4) $Constants.refinedExceptionMessage(e)");
【讨论】:
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