Multiple calls to set LiveData is not observed

Question

I have recently seen a weird issue that is acting as a barrier to my project. Multiple calls to set the live data value does not invoke the observer in the view.

It

Answer 1

I had such issue too.

To resolve it was created custom MutableLiveData, that contains a queue of posted values and will notify observer for each value.

You can use it the same way as usual MutableLiveData.

open class MultipleLiveEvent : MutableLiveData() {
private val mPending =
    AtomicBoolean(false)
private val values: Queue = LinkedList()

@MainThread
override fun observe(
    owner: LifecycleOwner,
    observer: Observer
) {
    if (hasActiveObservers()) {
        Log.w(
            this::class.java.name,
            "Multiple observers registered but only one will be notified of changes."
        )
    }
    // Observe the internal MutableLiveData
    super.observe(owner, Observer { t: T ->
        if (mPending.compareAndSet(true, false)) {
            observer.onChanged(t)
            //call next value processing if have such
            if (values.isNotEmpty())
                pollValue()
        }
    })
}

override fun postValue(value: T) {
    values.add(value)
    pollValue()
}

private fun pollValue() {
    setValue(values.poll())
}

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

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

}