我正在Xamarin中测试Firebase电话验证。以下是我采取的步骤：
1.添加NuGet包：Xamarin.Firebase.授权，Xamarin.Firebase.安卓项目的核心.
1.要启动电话号码验证：

• 添加类：帐户服务授权电话.cs

[assembly: Dependency(typeof(AccountServiceAuthPhone))]
namespace XXXXX.Droid
{
  public class AccountServiceAuthPhone : PhoneAuthProvider.OnVerificationStateChangedCallbacks, IAccountService
  {
      public AccountServiceAuthPhone()
      {
      }

      //const int OTP_TIMEOUT = 30; // seconds
      private string _verificationId;
      private FirebaseAuth mAuth;
      private PhoneAuthProvider.ForceResendingToken mResendToken;
      private PhoneAuthProvider.OnVerificationStateChangedCallbacks mCallbacks;

      public override void OnVerificationCompleted(PhoneAuthCredential credential)
      {
          System.Diagnostics.Debug.WriteLine("PhoneAuthCredential created Automatically");
      }

      public override void OnVerificationFailed(FirebaseException exception)
      {
          System.Diagnostics.Debug.WriteLine("Verification Failed: " + exception.Message);
      }

      public override void OnCodeSent(string verificationId, PhoneAuthProvider.ForceResendingToken forceResendingToken)
      {
          base.OnCodeSent(verificationId, forceResendingToken);
          _verificationId = verificationId;
      }
      public Task<bool> SendOtpCodeAsync(string phoneNumber)
      {
          PhoneAuthOptions options =
          PhoneAuthOptions.NewBuilder(mAuth)
                  .SetPhoneNumber(phoneNumber)       // Phone number to verify
                  .SetTimeout((Java.Lang.Long)60L, TimeUnit.Seconds) // Timeout and unit
                  .SetActivity(Platform.CurrentActivity)              // Activity (for callback binding)
                  .SetCallbacks(mCallbacks)   // OnVerificationStateChangedCallbacks
                  .Build();
          PhoneAuthProvider.VerifyPhoneNumber(options);
          return Task.FromResult(true);
      }

      private void OnAuthCompleted(Task task, TaskCompletionSource<bool> tcs)
      {
          if (task.IsCanceled || task.IsFaulted)
          {
              // something went wrong
              tcs.SetResult(false);
              return;
          }
          _verificationId = null;
          tcs.SetResult(true);
      }

      public Task<bool> VerifyOtpCodeAsync(string code)
      {
          if (!string.IsNullOrWhiteSpace(_verificationId))
          {
              var credential = PhoneAuthProvider.GetCredential(_verificationId, code);
              var tcs = new TaskCompletionSource<bool>();
              FirebaseAuth.Instance.SignInWithCredentialAsync(credential)
                  .ContinueWith((task) => OnAuthCompleted(task, tcs));
              return tcs.Task;
          }
          return Task.FromResult(false);
      }
  }
}

• 添加接口IAccountService.cs

public interface IAccountService
{        
    Task<bool> SendOtpCodeAsync(string phoneNumber);
    Task<bool> VerifyOtpCodeAsync(string code);
}

• Login.xaml.cs

private async void _nextlogin_Tapped(object sender, EventArgs e)
{
    if (txt_phone.Text != null && !string.IsNullOrWhiteSpace(txt_phone.Text.Trim().Replace("'", "").Replace("&", "")))
    {
      string phone = txt_phone.Text;

      await _accountService.SendOtpCodeAsync(phone);

      Preferences.Set("PhoneGetOTP", txt_phone.Text);
      await Navigation.PushAsync(new ConfirmOTP());
    }         
}

1.去谷歌云控制台，选择你的项目。
1.单击导航菜单并选择API &服务，然后选择 Jmeter 板。
1.点击启用API和服务，启用API“Android设备验证”。
1.添加SHA-1并下载，替换项目中最新的google-services.json文件。

但是，当我调试时，它给出了一个错误：“未将对象引用设置为对象”的示例。看起来它未执行到：public Task<bool> SendOtpCodeAsync(string phoneNumber).期待大家的帮助。谢谢