SingleLiveEvent

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

    private val mPending = 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.");
        }

        super.observe(owner, Observer {
            if (mPending.compareAndSet(true, false)) {
                observer.onChanged(it)
            }
        })
    }

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

    /**
     * Used for cases where T is Void, to make calls cleaner.
     */
    @MainThread
    fun call() {
        setValue(null)
    }

    companion object {

        private val TAG = "SingleLiveEvent"
    }
}