Live data observer getting called multiple times

Question

I have an Android app that shows a toast when user perform some actions like post deletion for example , a toast appears and says "post deleted" but if we turn the android phone on the horizontal the toast appears again and again never stop. how can i make the toast stop?

        postsViewModel.genericResponseLiveData.observe(this, Observer {
            when (it.status) {
                Status.LOADING -> { Timber.e("Loading...") }

                Status.SUCCESS -> {
                    when (it.item) {
                        GenericResponse.ITEM_RESPONSE.REPORT_POST -> toast("Post reported \uD83D\uDC4A")
                        else -> Timber.e("Success \uD83D\uDE03")
                    }
                }

                Status.ERROR -> { toast("${it.error}. Please try again") }
            }
        })
    } ```

user_5595926 · Answer

LiveData is not designed for single events.

Medium Blog

Using Event

/**
 * Used as a wrapper for data that is exposed via a LiveData that represents an event.
 */
open class Event(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
}

Easy Sample Usage

class ListViewModel : ViewModel {
    private val _navigateToDetails = MutableLiveData>()

    val navigateToDetails : LiveData>
        get() = _navigateToDetails


    fun userClicksOnButton(itemId: String) {
        _navigateToDetails.value = Event(itemId)  // Trigger the event by setting a new Event as a new value
    }
}

Activity

myViewModel.navigateToDetails.observe(this, Observer {
    it.getContentIfNotHandled()?.let { // Only proceed if the event has never been handled
        startActivity(DetailsActivity...)
    }
})

Wrap the relevant section in your code with Event.

user_2305239 · Answer

LiveData is sticky in nature which means whenever your fragment or activity becomes active it will receive the last value. So it's not good for 1 time event like showing a toast/dialog/snackbar.

You can use SingleLiveEvent like this: How to use Single Live Event to show toast in Kotlin

More detailed Article on this: https://medium.com/androiddevelopers/livedata-with-snackbar-navigation-and-other-events-the-singleliveevent-case-ac2622673150

user_12401637 · Answer

You can make Status livedata to null after you observed it and check for null inside the observer if your livedata is null then just return

Live data observer getting called multiple times

3 Answers