Assuming I need to fetch a list of Password and Category, merging them into a single LiveData.
First, I create a Sealed Classes to represent both data type.
sealed class MergedDatadata class PasswordData(val passwordItems: List<Password>): MergedData()data class CategoryData(val categoryItems: List<Category>): MergedData()Then I create a MediatorLiveData to fetch both data type.
fun fetchData(): MediatorLiveData<MergedData> { val liveDataMerger = MediatorLiveData<MergedData>() liveDataMerger.addSource(passwordDataSource.fetchAll(), { if (it != null) { liveDataMerger.value = PasswordData(it) } }) liveDataMerger.addSource(categoryDataSource.fetchAll(), { if (it != null) { liveDataMerger.value = CategoryData(it) } }) return liveDataMerger}Lastly I observe the LiveData and make sure both data sets are received before processing.
val liveData = fetchData()var passwordItems: List<Password>? = nullvar categoryItems: List<Category>? = nullliveData.observe(activity, object : Observer<MergedData> { override fun onChanged(it: MergedData?) { when (it) { is PasswordData -> passwordItems = it.passwordItems is CategoryData -> categoryItems = it.categoryItems } if (passwordItems != null && categoryItems != null) { // both data is ready, proceed to process them // stop observing liveData.removeObserver(this) } }})