Using live data, how to display a dialog only once?

Question

I want to display an alert with a message using live data. The problem I have is whenever the activity is resumed the alert pops up again. Any hints?

Answer 1

You could use a custom live event that is triggered only once. This discussion has already took place on Android's Architecture Google Samples Repository. Here's a proposed solution I like.

In case you need it in kotlin, there it goes:

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

    private val pending = AtomicBoolean(false)

    @MainThread
    override fun observe(owner: LifecycleOwner, observer: Observer<T>) {
        if (hasActiveObservers()) {
            Log.w(TAG, "Multiple observers registered but only one will be notified of changes.")
        }

        // Observe the internal MutableLiveData
        super.observe(owner, Observer<T> { t ->
            if (pending.compareAndSet(true, false)) {
                observer.onChanged(t)
            }
        })
    }

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

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

    companion object {

        private val TAG = "SingleLiveEvent"
    }
}

Using this it won't trigger you dialogs twice unless you call yourLiveData.value = newValue again.

Hope it helps.

Answer 2

Set a boolean isShown = false;

When you show the dialog set it to true and save it to Shared preferences. show the dialog only isShown is false.