How to combine two live data one after the other?

Question

I have next use case: User comes to registration form, enters name, email and password and clicks on register button. After that system needs to check if email is taken or n

Answer 1

I did an approach based on @guness answer. I found that being limited to two LiveDatas was not good. What if we want to use 3? We need to create different classes for every case. So, I created a class that handles an unlimited amount of LiveDatas.

/**
  * CombinedLiveData is a helper class to combine results from multiple LiveData sources.
  * @param liveDatas Variable number of LiveData arguments.
  * @param combine   Function reference that will be used to combine all LiveData data results.
  * @param R         The type of data returned after combining all LiveData data.
  * Usage:
  * CombinedLiveData(
  *     getLiveData1(),
  *     getLiveData2(),
  *     ... ,
  *     getLiveDataN()
  * ) { datas: List ->
  *     // Use datas[0], datas[1], ..., datas[N] to return a SomeType value
  * }
  */
 class CombinedLiveData(vararg liveDatas: LiveData<*>,
                           private val combine: (datas: List) -> R) : MediatorLiveData() {

      private val datas: MutableList = MutableList(liveDatas.size) { null }

      init {
         for(i in liveDatas.indices){
             super.addSource(liveDatas[i]) {
                 datas[i] = it
                 value = combine(datas)
             }
         }
     }
 }