RxJava2: Have an action (like a loading spinner) be invoked when an observable takes a long time and not instantaneously

delayedaction.md

/**
 * Invoke some action when the observable does not emit an item for longer than a given time out
 * @param timeout time out
 * @param timeUnit the unit for the time out
 * @param scheduler the scheduler on which the action must be ran
 * @param action the action to invoke
 */
fun <T> Observable<T>.startAfterDelay(timeout: Long, timeUnit: TimeUnit, scheduler: Scheduler, action: () -> Unit): Observable<T> {
    return this.publish { o ->
        o.timeout(timeout, timeUnit, scheduler) {
            action.invoke()
        }.mergeWith(o)
    }
}