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/*
* This file is part of GNU Taler
* (C) 2020 Taler Systems S.A.
*
* GNU Taler is free software; you can redistribute it and/or modify it under the
* terms of the GNU General Public License as published by the Free Software
* Foundation; either version 3, or (at your option) any later version.
*
* GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
* WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
* A PARTICULAR PURPOSE. See the GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along with
* GNU Taler; see the file COPYING. If not, see <http://www.gnu.org/licenses/>
*/
package net.taler.common
import androidx.lifecycle.LiveData
import androidx.lifecycle.Observer
import java.util.concurrent.atomic.AtomicBoolean
/**
* Used as a wrapper for data that is exposed via a [LiveData] that represents an one-time event.
*/
open class Event<out T>(private val content: T) {
private val isConsumed = AtomicBoolean(false)
/**
* Returns the content and prevents its use again.
*/
fun getIfNotConsumed(): T? {
return if (isConsumed.compareAndSet(false, true)) content else null
}
}
fun <T> T.toEvent() = Event(this)
/**
* An [Observer] for [Event]s, simplifying the pattern of checking if the [Event]'s content has
* already been consumed.
*
* [onEvent] is *only* called if the [Event]'s contents has not been consumed.
*/
class EventObserver<T>(private val onEvent: (T) -> Unit) : Observer<Event<T>> {
override fun onChanged(event: Event<T>?) {
event?.getIfNotConsumed()?.let { onEvent(it) }
}
}
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