await 关键字不在飞镖中等待

Question

我正在使用 await 关键字等待方法完成并返回某些内容，然后使用 switch 语句根据方法返回值执行代码块，但它不会等待它的值，当我尝试打印输出为null的值！

代码如下：

 PhoneNumVerification status = await accountRecoveryAdmin.verifyUserPhoneNumber(phoneNum);
 print(status); // prints null because it didn't wait for the method to complete
 switch (status) {
 // some code
 }

方法如下：

enum PhoneNumVerification {
     failed,
     verified,
     wrongInput,
     smsVerificationNeeded
}

Future<PhoneNumVerification> verifyUserPhoneNumber(String phoneNum) async {
if (phoneNum.isEmpty ||
    !phoneNum.startsWith('01') ||
    phoneNum.length != 11) {
  return PhoneNumVerification.wrongInput;
}
try {
  await _auth.verifyPhoneNumber(
    phoneNumber: '+2$phoneNum',
    timeout: Duration(seconds: 30),
    verificationCompleted: (_) {
      return PhoneNumVerification.verified;
    },
    verificationFailed: (exception) {
      print(exception.message);
      return PhoneNumVerification.failed;
    },
    codeSent: (String verificationId, [int forceResendingToken]) {
      this.verificationId = verificationId;
      return PhoneNumVerification.smsVerificationNeeded;
    },
    codeAutoRetrievalTimeout: null,
  );
} catch (e) {
  print(e);
  return PhoneNumVerification.failed;
}
}

Answer 1

await accountRecoveryAdmin.verifyUserPhoneNumber(...) 确实在等待。问题是accountRecoveryAdmin.verifyUserPhoneNumber() 没有返回值。如果您在代码上运行dartanalyzer，它应该报告并非所有通过verifyUserPhoneNumber 的路径都返回一个值。

这是您的代码的简化版本，以使问题更加明显：

Future<PhoneNumVerification> verifyUserPhoneNumber(String phoneNum) async {
  // ...

  try {
    await _auth.verifyPhoneNumber(
      // ...
    );
  } catch (e) {
    print(e);
    return PhoneNumVerification.failed;
  }
}

您可以看到try 块没有返回值。它传递了具有return 语句的回调，但这只是指定了这些回调返回的内容；它们不是verifyUserPhoneNumber 返回的。

修复它的一种方法是让这些回调在verifyUserPhoneNumber 的范围内设置一个变量，然后返回：

Future<PhoneNumVerification> verifyUserPhoneNumber(String phoneNum) async {
  // ...

  try {
    PhoneNumVerification result;
    await _auth.verifyPhoneNumber(
      // ...
      verificationCompleted: (_) {
        result = PhoneNumVerification.verified;
      },
      verificationFailed: (exception) {
        // ...
        result = PhoneNumVerification.failed;
      },
      codeSent: (String verificationId, [int forceResendingToken]) {
        // ...
        result = PhoneNumVerification.smsVerificationNeeded;
      },
      // ...
    );

    return result;
  } catch (e) {
    print(e);
    return PhoneNumVerification.failed;
  }
}

编辑：

我不清楚FirebaseAuth.verifyPhoneNumber 返回的Future 代表什么。它可能只是表示请求已发送，而不是验证已完成。如果您希望您的功能等待验证完成，您可以这样做：

Future<PhoneNumVerification> verifyUserPhoneNumber(String phoneNum) async {
  // ...

  try {
    final verificationComplete = Completer<PhoneNumVerification>();
    await _auth.verifyPhoneNumber(
      // ...
      verificationCompleted: (_) {
        verificationComplete.complete(PhoneNumVerification.verified);
      },
      verificationFailed: (exception) {
        // ...
        verificationComplete(PhoneNumVerification.failed);
      },
      codeSent: (String verificationId, [int forceResendingToken]) {
        // ...
        verificationComplete(PhoneNumVerification.smsVerificationNeeded);
      },
      // ...
    );

    return await verificationComplete.future;
  } catch (e) {
    print(e);
    return PhoneNumVerification.failed;
  }
}