flutter - Flutter 中的异步函数未返回预期数据

Question

我正在尝试使用 firebase 验证电话号码。但从异步函数中得到了意想不到的结果。这是我的代码:

  bool isVerificationSuccess = false;

  Future<bool> verifyUserPhoneNumber(String phoneNumber) async {
    await FirebaseAuth.instance.verifyPhoneNumber(
      phoneNumber: phoneNumber,
      timeout: Duration(seconds: 60),
      verificationCompleted: (credential) => verificationComplete(credential),
      verificationFailed: (authException) => verificationFailed(authException),
      codeAutoRetrievalTimeout: (verificationId) =>
          codeAutoRetrievalTimeout(verificationId),
      codeSent: (verificationId, [code]) => smsCodeSent(verificationId, [code]),
    );
    print("Status from service : $isVerificationSuccess");
    return isVerificationSuccess;
  }

  verificationComplete(AuthCredential credential) async {
    FirebaseUser user = await FirebaseAuth.instance.currentUser();

    user.linkWithCredential(credential).then((_) {
      print("User Successfully Linked");
      isVerificationSuccess = true;
    }).catchError((e) {
      print("Linking Error : ${e.toString()}");
    });
  }

这是输出:

 Status from service : false
 User Successfully Linked

因此，这里 verifyUserPhoneNumber 函数甚至在 FirebaseAuth.instance.verifyPhoneNumber() 完成之前就返回，因此它不会返回预期数据(始终 false >) 即使验证成功。这里出了什么问题？

Answer 1

问题在于这一行中的函数调用:

verificationCompleted: (credential) => verificationComplete(credential),

即使函数本身是异步的，也不会等待

。那么会发生什么:

1. verifyUserPhoneNumber 从某处调用
2. FirebaseAuth.instance.verifyPhoneNumber 正在等待
3. 在此调用中，将调用 verificationComplete(credential)，并且由于它本身包含一个等待语句，因此它将由 Dart 事件循环排队。因此，无论 FirebaseUser user = wait FirebaseAuth.instance.currentUser(); 之后发生的事情都会被延迟!
4. verifyUserPhoneNumber 现在继续执行并返回 false。
5. 返回值后，现在轮到 verificationComplete 进行处理。它将更改 bool 值，然后退出。

我在这里的建议是不要使用全局变量，而是，例如，在 FirebaseAuth.instance.verifyPhoneNumber 之后调用 verificationComplete after已完全处理完毕并返回。

编辑:这就是理论上解决问题的方法，尽管我承认它不是特别漂亮:

  Future<bool> verifyUserPhoneNumber(String phoneNumber) async {
    final completer = Completer<AuthCredential>();
    await FirebaseAuth.instance.verifyPhoneNumber(
      phoneNumber: phoneNumber,
      timeout: Duration(seconds: 60),
      verificationCompleted: completer.complete,
      verificationFailed: completer.completeError,
      codeAutoRetrievalTimeout: (verificationId) =>
          codeAutoRetrievalTimeout(verificationId),
      codeSent: (verificationId, [code]) => smsCodeSent(verificationId, [code]),
    );
    try {
      final credential = await completer.future;
      return await verificationComplete(credential);
    } catch (e) {
      verificationFailed(e);
      return false;
    }
  }

  Future<bool> verificationComplete(AuthCredential credential) async {
    FirebaseUser user = await FirebaseAuth.instance.currentUser();
    try {
      await user.linkWithCredential(credential);
      print("User Successfully Linked");
      return true;
    } catch (e) {
      print("Linking Error : ${e.toString()}");
      return false;
    }
  }