Notify Observer when item is added to List of LiveData

Question

I need to get an Observer event when the item is added to the List of LiveData. But as far as I understand the event receives only when I replace the old list with a new one

Answer 1

Inspired by @user3682351 here is my solution. It seems that we cannot update properties of a LiveData value individually so the value must be updated on each operation. This is essentially a small wrapper on live data with convenience methods for modifying properties of a HashMap

import androidx.lifecycle.LiveData

/**
 * Hash Map Live Data
 *
 * Some convenience methods around live data for HashMaps. Putting a value on this will also update the entire live data
 * as well
 */
class HashMapLiveData : LiveData>() {

    /**
     * Put a new value into this HashMap and update the value of this live data
     * @param k the key
     * @param v the value
     */
    fun put(k: K, v: V) {
        val oldData = value
        value = if (oldData == null) {
            hashMapOf(k to v)
        } else {
            oldData.put(k, v)
            oldData
        }
    }

    /**
     * Add the contents to the HashMap if there is one existing, otherwise set the value to this HashMap and update the
     * value of this live data
     * @param newData the HashMap of values to add
     */
    fun putAll(newData: HashMap) {
        val oldData = value
        value = if (oldData != null) {
            oldData.putAll(newData)
            oldData
        } else {
            newData
        }
    }

    /**
     * Remove a key value pair from this HashMap and update the value of this live data
     * @param key the key to remove
     */
    fun remove(key: K) {
        val oldData = value
        if (oldData != null) {
            oldData.remove(key)
            value = oldData
        }
    }

    /**
     * Clear all data from the backing HashMap and update the value of this live data
     */
    fun clear() {
        val oldData = value
        if (oldData != null) {
            oldData.clear()
            value = oldData
        }
    }

    var value: HashMap?
        set(value) = super.setValue(value)
        get() = super.getValue()

}