更新Firebase SDK后PhoneCallbacks类未实现抽象成员报错如何解决

错误信息中文释义：PhoneCallBacks.kt 第6行第1列：类 PhoneCallbacks 不是抽象类，且未实现抽象基类成员方法 public abstract fun onVerificationCompleted(p0: PhoneAuthCredential): Unit（该方法定义在 com.google.firebase.auth.PhoneAuthProvider.OnVerificationStateChangedCallbacks 中）

问题根因 #

这是Firebase Auth SDK版本升级带来的不兼容变更：新版SDK中OnVerificationStateChangedCallbacks的三个回调方法参数全部改为非空类型，你现有代码里重写的方法参数都添加了可空标记?，导致方法签名和父类的抽象方法不匹配，编译器判定你没有实现对应抽象方法，因此抛出编译错误。

修复方案 #

方案1：同步修改为非空参数（推荐） #

新版Firebase Auth的回调参数不会为空，直接调整所有相关方法的参数类型即可：

class PhoneCallbacks(private val listener : PhoneCallbacksListener) : PhoneAuthProvider.OnVerificationStateChangedCallbacks() {

    interface PhoneCallbacksListener {
        fun onVerificationCompleted(credential: PhoneAuthCredential)
        fun onVerificationFailed(exception: FirebaseException)
        fun onCodeSent(
                verificationId: String,
                token: PhoneAuthProvider.ForceResendingToken
        )
    }

    override fun onVerificationCompleted(phoneAuthCredential: PhoneAuthCredential) {
        listener.onVerificationCompleted(phoneAuthCredential)
    }

    override fun onVerificationFailed(exception: FirebaseException) {
        listener.onVerificationFailed(exception)
    }

    override fun onCodeSent(verificationId: String, token: PhoneAuthProvider.ForceResendingToken) {
        listener.onCodeSent(verificationId,token)
    }
}

方案2：兼容原有可空逻辑 #

如果不想修改原有Listener的调用逻辑，只需要调整重写方法的参数签名，保持Listener的可空定义即可：

class PhoneCallbacks(private val listener : PhoneCallbacksListener) : PhoneAuthProvider.OnVerificationStateChangedCallbacks() {

    interface PhoneCallbacksListener {
        fun onVerificationCompleted(credential: PhoneAuthCredential?)
        fun onVerificationFailed(exception: FirebaseException?)
        fun onCodeSent(
                verificationId: String?,
                token: PhoneAuthProvider.ForceResendingToken?
        )
    }

    override fun onVerificationCompleted(phoneAuthCredential: PhoneAuthCredential) {
        listener.onVerificationCompleted(phoneAuthCredential)
    }

    override fun onVerificationFailed(exception: FirebaseException) {
        listener.onVerificationFailed(exception)
    }

    override fun onCodeSent(verificationId: String, token: PhoneAuthProvider.ForceResendingToken) {
        listener.onCodeSent(verificationId,token)
    }
}

内容的提问来源于stack exchange，提问作者DB_cont