An event wrapper for data that is exposed via a LiveData that represents an event.

Event.kt

/**
 * Used as a wrapper for data that is exposed via a LiveData that represents an event.
 */
open class Event<out T>(private val content: T) {

    var hasBeenHandled = false
        private set // Allow external read but not write

    /**
     * Returns the content and prevents its use again.
     */
    fun getContentIfNotHandled(): T? {
        return if (hasBeenHandled) {
            null
        } else {
            hasBeenHandled = true
            content
        }
    }

    /**
     * Returns the content, even if it's already been handled.
     */
    fun peekContent(): T = content
}

That looks nearly like my latest solution. However, I don't use a special EventObserver, since a Kotlin extension function can do the job:

class Event<out T>(private val content: T) {
    private val consumedScopes = HashSet<String>()

Adding more syntactic sugar to choirwire's contribution

class Event<out T>(private val content: T) {
    private val consumedScopes by lazy { HashSet<String>() }

    fun isConsumed(scope: String = "") = scope in consumedScopes

    @MainThread
    fun consume(scope: String = ""): T? {
        return content.takeIf { !isConsumed(scope) }?.also { consumedScopes.add(scope) }
    }

    fun peek(): T = content
}