flutter - 异步函数未在Flutter中返回预期数据

Question

我正在尝试使用Firebase验证电话号码。但是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，因此即使验证成功，它也不会返回预期数据(总是 false)。怎么了

Answer 1

问题是此行中的函数调用:

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

即使函数本身是异步的，也不会等待。所以发生的是:

verifyUserPhoneNumber从

某个地方调用

FirebaseAuth.instance.verifyPhoneNumber正在等待

在此调用中，调用了verificationComplete(credential)，由于它本身包含一个await语句，它将被Dart事件循环排队。所以FirebaseUser user = await FirebaseAuth.instance.currentUser();延迟之后会发生什么!

verifyUserPhoneNumber现在继续执行并返回false。

在返回值之后，现在就转到verificationComplete进行处理。它将更改 bool(boolean) 值，然后退出。

我在这里的建议不是使用全局变量，而是例如，在 verificationComplete已经完全完成处理并返回之后，调用 FirebaseAuth.instance.verifyPhoneNumber。

编辑:尽管我认为它不是特别漂亮，但是从理论上讲这是解决问题的方法:

  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;
    }
  }