private void sendVerificationCode(){
    String phoneN =phone.getText().toString();
    
    PhoneAuthProvider.getInstance().verifyPhoneNumber(
            phoneN,                           
            60,                  
            TimeUnit.SECONDS,   
            Registration.this,               
            mCallbacks);        
}
PhoneAuthProvider.OnVerificationStateChangedCallbacks mCallbacks= new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
    @Override
    public void onVerificationCompleted(PhoneAuthCredential phoneAuthCredential) {
        Toast.makeText(Registration.this,"验证完成",Toast.LENGTH_SHORT).show();
        signInWithPhoneAuthCredential(phoneAuthCredential);
    }
    @Override
    public void onVerificationFailed(FirebaseException e) {
        Toast.makeText(Registration.this,"验证失败",Toast.LENGTH_SHORT).show();
    }
    @Override
    public void onCodeSent(String s, PhoneAuthProvider.ForceResendingToken forceResendingToken) {
        codeSent=s;
    }
};
private void VerifyCode(){
    String code= otp.getText().toString();
    PhoneAuthCredential credential = PhoneAuthProvider.getCredential(codeSent, code);
    signInWithPhoneAuthCredential(credential);
}
private void signInWithPhoneAuthCredential(PhoneAuthCredential credential) {
    mAuth.signInWithCredential(credential)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if (task.isSuccessful()) {
                        Toast.makeText(getApplicationContext(),"欢迎，现在您可以登录", Toast.LENGTH_LONG).show();
                        Intent intent = new Intent(Registration.this,Login_Reg.class);
                        startActivity(intent);
                    } else {
                        if (task.getException() instanceof FirebaseAuthInvalidCredentialsException) {
                            // 输入的验证码无效
                            Toast.makeText(getApplicationContext(),"验证码不正确",Toast.LENGTH_LONG).show();
                        }
                    }
                }
            });
}
}