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

With the help of MediatorLiveData, you can combine results from multiple sources. Here an example of how would I combine two sources:

class CombinedLiveData(source1: LiveData, source2: LiveData, private val combine: (data1: T?, data2: K?) -> S) : MediatorLiveData() {

private var data1: T? = null
private var data2: K? = null

init {
    super.addSource(source1) {
        data1 = it
        value = combine(data1, data2)
    }
    super.addSource(source2) {
        data2 = it
        value = combine(data1, data2)
    }
}

override fun  addSource(source: LiveData, onChanged: Observer) {
    throw UnsupportedOperationException()
}

override fun  removeSource(toRemove: LiveData) {
    throw UnsupportedOperationException()
}
}

here is the gist for above, in case it is updated on the future: https://gist.github.com/guness/0a96d80bc1fb969fa70a5448aa34c215