我如何知道Firebase是否是第一次登录？数据存在吗？

Question

这是Firebase匿名登录代码。

我想知道如何编写if(????)

当我读取数据时，我认为如果没有数据，它将是null。

DBreference.Child("UserData").Child(fireUser .UserId).GetValueAsync()

此代码不为空

auth = FirebaseAuth.DefaultInstance;
DBreference = FirebaseDatabase.DefaultInstance.RootReference;
User userData = null; // User class include userdata

auth.SignInAnonymouslyAsync().ContinueWith(task =>
{
 fireUser = task.Result;
 //Always automatically login success

 //This part is read Data from Firebase.Database
 DBreference.Child("UserData").Child(fireUser.UserId).
 GetValueAsync().ContinueWith(task2 => 
 {
     if(????) // data dosen't exist
     {
         userData = new User();
         string jsonString = JsonFx.Json.JsonWriter.Serialize(userData);
         DBreference.Child("UserData").Child(fireUser.UserId).
         SetRawJsonValueAsync(jsonString);
     }
     else // data exists
     { 
         jsonString = task2.Result.GetRawJsonValue();
         userData = JsonFx.Json.JsonReader.Deserialize<User>(jsonString);            
     }
 });
});

Answer 1

好的，在读完你的评论后，我现在明白了你需要交换if/else之后你是什么

auth = FirebaseAuth.DefaultInstance;
DBreference = FirebaseDatabase.DefaultInstance.RootReference;

auth.SignInAnonymouslyAsync().ContinueWith(task =>
{
 fireUser = task.Result;

 if(task.IsFaulted) // user doesn't exist
 { 
   userData = new User(); 
   string jsonString = JsonFx.Json.JsonWriter.Serialize(userData);
   DBreference.Child("UserData").Child(fireUser .UserId).           
   SetRawJsonValueAsync(jsonString);
 }
 else //user exists
 {
    DBreference.Child("UserData").Child(fireUser .UserId).
    GetValueAsync().ContinueWith(task3 =>
    {
        jsonString = task3.Result.GetRawJsonValue();      
        userData = JsonFx.Json.JsonReader.Deserialize<User>(jsonString);
    });
 }
});