Refreshing MutableLiveData of list of items

I think the extension is a bit nicer.

operator fun <T> MutableLiveData<ArrayList<T>>.plusAssign(values: List<T>) {
    val value = this.value ?: arrayListOf()
    value.addAll(values)
    this.value = value
}

Usage:

list += anotherList;

According to MutableLiveData, you need to use postValue or setValue in order to trigger the observers.