The snippet to show when update callback is called.

AsyncPagingDataDifferTest.kt

import androidx.paging.AsyncPagingDataDiffer
import androidx.paging.PagingData
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.ListUpdateCallback
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.runBlocking

val differ: AsyncPagingDataDiffer<String> by lazy {
    AsyncPagingDataDiffer(
        diffCallback = diffCallback,
        updateCallback = updateCallback,
        mainDispatcher = Dispatchers.Unconfined,
        workerDispatcher = Dispatchers.Unconfined,
    )
}

val diffCallback = object : DiffUtil.ItemCallback<String>() {
    override fun areItemsTheSame(oldItem: String, newItem: String) = oldItem.first() == newItem.first()
    override fun areContentsTheSame(oldItem: String, newItem: String) = oldItem == newItem
}

val updateCallback = object : ListUpdateCallback {
    override fun onInserted(position: Int, count: Int) {
        println("onInserted: ${differ.snapshot()}")
    }

    override fun onRemoved(position: Int, count: Int) {
        println("onRemoved: ${differ.snapshot()}")
    }

    override fun onMoved(fromPosition: Int, toPosition: Int) {
        println("onMoved: ${differ.snapshot()}")
    }

    override fun onChanged(position: Int, count: Int, payload: Any?) {
        println("onChanged: ${differ.snapshot()}")
    }
}

differ.addLoadStateListener {
    println("loadStateListener: ${differ.snapshot()}")
}

runBlocking {
    println()
    differ.submitData(PagingData.from(listOf("A", "B", "C")))
    println("after onInserted: ${differ.snapshot()}")
    println()
    differ.submitData(PagingData.from(listOf("A", "C")))
    println("after onRemoved: ${differ.snapshot()}")
    println()
    differ.submitData(PagingData.from(listOf("C", "A")))
    println("after onMoved: ${differ.snapshot()}")
    println()
    differ.submitData(PagingData.from(listOf("Changed", "A")))
    println("after onChanged: ${differ.snapshot()}")
}

Output:

loadStateListener: []

onInserted: []
loadStateListener: [A, B, C]
after onInserted: [A, B, C]

onRemoved: [A, B, C]
after onRemoved: [A, C]

onMoved: [A, C]
after onMoved: [C, A]

onChanged: [C, A]
after onChanged: [Changed, A]

Expected that snapshot in the callback and after callback will be the same. LoadStateListener not always triggered on data change.