live data that emits only once i.e, events

EventLiveData.kt

package com.sensehawk.presentation

import android.arch.lifecycle.LifecycleOwner
import android.arch.lifecycle.MutableLiveData
import android.arch.lifecycle.Observer
import android.support.annotation.MainThread
import java.util.concurrent.atomic.AtomicBoolean

class EventLiveData<T> : MutableLiveData<T>() {

  private val pending = AtomicBoolean(false)
  private val observers = mutableSetOf<Observer<T>>()

  private val internalObserver = Observer<T> { t ->
    if (pending.compareAndSet(true, false)) {
      observers.forEach { observer ->
        observer.onChanged(t)
      }
    }
  }

  @MainThread
  override fun observe(owner: LifecycleOwner, observer: Observer<T>) {
    observers.add(observer)

    if (!hasObservers()) {
      super.observe(owner, internalObserver)
    }
  }

  override fun removeObservers(owner: LifecycleOwner) {
    observers.clear()
    super.removeObservers(owner)
  }

  override fun removeObserver(observer: Observer<T>) {
    observers.remove(observer)
    super.removeObserver(observer)
  }

  @MainThread
  override fun setValue(t: T?) {
    pending.set(true)
    super.setValue(t)
  }

  @MainThread
  fun call() {
    value = null
  }
}