SingleLiveEvent

class SingleLiveEvent<T> : MutableLiveData<T>() {
    private val pending = AtomicBoolean(false)
    @MainThread
    override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
        if (hasActiveObservers()) {
            Log.w(TAG, "Multiple observers registered but only one will be notified of changes.")
        }
        // Observe the internal MutableLiveData
        super.observe(owner, { t ->
            if (pending.compareAndSet(true, false)) {
                observer.onChanged(t)
            }
        })
    }

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

    operator fun invoke(t: T?){
        value = t
    }

    /**
     * Used for cases where T is Void, to make calls cleaner.
     */
    @MainThread
    fun call() {
        value = null
    }
    companion object {
        private const val TAG = "SingleLiveEvent"
    }
}