A MutableList- and CollectionLiveData implementation based on Android Architecture Components LiveData which allows to get notified on collection changes.

MutableCollectionLiveData.kt

/*
 * Copyright [2019] [Tobias Boehm]
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or    implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
import androidx.lifecycle.MutableLiveData

/**
 * This is an implementation of [MutableLiveData] that provides a subset of [MutableCollection] methods which
 * change the list content and trigger an observer notification.
 */
open class MutableCollectionLiveData<DataType, ContainerType : MutableCollection<DataType>> : MutableLiveData<ContainerType>(), Collection<DataType>
{
    // region Set Member Vars
    // =================================================================================================================================================================================================
    override val size: Int
        get() = throwIfCollectionIsNullOrExecute { it.size }
    // endregion

    // region Mutable Collection Methods which change state
    // =================================================================================================================================================================================================
    fun add(element: DataType): Boolean = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.add(element) } }

    fun addAll(elements: Collection<DataType>): Boolean = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.addAll(elements) } }

    fun clear() = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.clear() } }

    fun remove(element: DataType): Boolean = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.remove(element) } }

    fun removeAll(elements: Collection<DataType>): Boolean = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.removeAll(elements) } }

    fun retainAll(elements: Collection<DataType>): Boolean = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.retainAll(elements) } }

    // endregion


    // region Collection Methods
    // =================================================================================================================================================================================================
    override fun contains(element: DataType): Boolean = throwIfCollectionIsNullOrExecute { it.contains(element) }

    override fun containsAll(elements: Collection<DataType>): Boolean = throwIfCollectionIsNullOrExecute { it.containsAll(elements) }

    override fun isEmpty(): Boolean = throwIfCollectionIsNullOrExecute { it.isEmpty() }

    override fun iterator(): Iterator<DataType> = throwIfCollectionIsNullOrExecute { it.iterator() }

    // endregion

    // region Public Methods
    // =================================================================================================================================================================================================
    fun isCollectionNotNull() : Boolean = value != null
    // endregion

    // region Private Methods
    // =================================================================================================================================================================================================
    protected fun <T> throwIfCollectionIsNullOrExecute(pCode: (collection: ContainerType) -> T): T
    {
        val collection = value
        if (collection == null)
        {
            throw IllegalStateException("You can't do that on a null list")
        }
        else
        {
            return pCode(collection)
        }
    }

    protected fun <T> executeAndNotify(pSet: ContainerType, pCode: (list: ContainerType) -> T): T = pCode(pSet).also { postValue(pSet) }
    // endregion
}

MutableListLiveData.kt

/*
 * Copyright [2018] [Tobias Boehm]
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or    implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */

import androidx.lifecycle.MutableLiveData

/**
 * This is an implementation of [MutableLiveData] that provides a subset of [MutableList] methods which
 * change the list content and trigger an observer notification.
 */
class MutableListLiveData<E> : MutableCollectionLiveData<E,MutableList<E>>(), List<E>
{

    // region MutableList Methods which change state
    // =================================================================================================================================================================================================
    fun add(index: Int, element: E) = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.add(index, element) } }

    fun addAll(index: Int, elements: Collection<E>): Boolean = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.addAll(index, elements) } }

    fun removeAt(index: Int): E = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.removeAt(index) } }

    fun set(index: Int, element: E): E = throwIfCollectionIsNullOrExecute { list -> executeAndNotify(list) { it.set(index, element) } }

    // endregion

    // region List Methods
    // =================================================================================================================================================================================================

    override fun get(index: Int): E = throwIfCollectionIsNullOrExecute { it.get(index) }

    override fun indexOf(element: E): Int = throwIfCollectionIsNullOrExecute { it.indexOf(element) }

    override fun lastIndexOf(element: E): Int = throwIfCollectionIsNullOrExecute { it.lastIndexOf(element) }

    override fun listIterator(): ListIterator<E> = throwIfCollectionIsNullOrExecute { it.listIterator() }

    override fun listIterator(index: Int): ListIterator<E> = throwIfCollectionIsNullOrExecute { it.listIterator(index) }

    override fun subList(fromIndex: Int, toIndex: Int): List<E> = throwIfCollectionIsNullOrExecute { it.subList(fromIndex, toIndex) }
    // endregion

}

copyright added; package declaration removed;

MutableCollectionLiveData.kt added - it can also be used for sets

Example usage that works for me:

Inside view model:

val locations: MutableListLiveData<LatLng> = MutableListLiveData<LatLng>().apply {
    postValue(mutableListOf())
}

On the Activity:

viewModel.locations.observe(this as LifecycleOwner) { locations ->
    try {
        val bounds = LatLngBounds.builder()
            .includeAll(locations)
            .build()

        Timber.i("Detected ${locations.size} locations in map.")
        googleMap.moveCamera(CameraUpdateFactory.newLatLngBounds(bounds, 30))
    } catch (e: IllegalStateException) {
        Timber.e("No markers were loaded.")
    }
}