JoseAlcerreca

/**
* Sets the value to the result of a function that is called when both `LiveData`s have data
* or when they receive updates after that.
*/
fun <T, A, B> LiveData<A>.combineAndCompute(other: LiveData<B>, onChange: (A, B) -> T): MediatorLiveData<T> {

   var source1emitted = false
   var source2emitted = false

   val result = MediatorLiveData<T>()

JoseAlcerreca

/**
* Notifies the event LiveData of a new request for a random number.
*/
fun onGetNumber() {
   newNumberEvent.value = Event(Unit)
}

JoseAlcerreca

private val newNumberEvent = MutableLiveData<Event<Any>>()

val randomNumber: LiveData<Int> = Transformations.switchMap(newNumberEvent) {
   numberGenerator.getNumber()
}

JoseAlcerreca

viewmodel.randomNumber.observe(this, Observer { number ->
    numberTv.text = resources.getString(R.string.random_text, number)
})

JoseAlcerreca

var lateinit randomNumber: LiveData<Int>

/**
 * Called on button click.
 */
fun onGetNumber() {
   randomNumber = Transformations.map(numberGenerator.getNumber()) {
       it
   }
}

JoseAlcerreca

val randomNumber = MediatorLiveData<Int>()

/**
* *Don't do this.*
*
* Called when the user clicks on a button
*
* This function adds a new source to the result but it doesn't remove the previous ones.
*/
fun onGetNumber() {

JoseAlcerreca

class SlowRandomNumberGenerator {
    private val rnd = Random()

    fun getNumber(): LiveData<Int> {
        val result = MutableLiveData<Int>()

        // Send a random number after a while
        Executors.newSingleThreadExecutor().execute {
            Thread.sleep(500)
            result.postValue(rnd.nextInt(1000))

JoseAlcerreca

class SharedLiveDataSource(val dataSource: MyDataSource) {
    fun loadDataForUser(userId: String): LiveData<Long> {
        val result = MutableLiveData<Long>()
        result.value = dataSource.getOnlineTime(userId)
        return result
    }
}

JoseAlcerreca

sharedLiveDataSource.loadDataForUser("2").observe(this, Observer {
   // Show result on screen
}) 

JoseAlcerreca

sharedLiveDataSource.loadDataForUser("1").observe(this, Observer {
   // Show result on screen
})