LiveData Event that only emits if it has not been consumed. From Florina Muntenescu's KotlinConf 2018 presentation: https://youtu.be/Sy6ZdgqrQp0?t=1579

Event.kt

open class Event<out T>(private val content: T) {
    var consumed = false
        private set

    fun consume(): T? {
        return if (consumed) {
            null
        } else {
            consumed = true
            content
        }
    }
}