FragmentStateListAdapter.kt

import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import androidx.fragment.app.FragmentManager
import androidx.lifecycle.Lifecycle
import androidx.recyclerview.widget.AsyncListDiffer
import androidx.recyclerview.widget.AsyncListDiffer.ListListener
import androidx.recyclerview.widget.DiffUtil
import androidx.viewpager2.adapter.FragmentStateAdapter

abstract class FragmentStateListAdapter<T>(
    fragmentManager: FragmentManager,
    lifecycle: Lifecycle,
    diffCallback: DiffUtil.ItemCallback<T>,
) : FragmentStateAdapter(fragmentManager, lifecycle) {

    val currentList: List<T> get() = _differ.currentList

    @Suppress("LeakingThis")
    private val _differ = AsyncListDiffer(this, diffCallback)


    init {
        _differ.addListListener { previousList, currentList ->
            onCurrentListChanged(previousList, currentList)
        }
    }

    constructor(
        fragment: Fragment,
        diffCallback: DiffUtil.ItemCallback<T>,
    ) : this(
        fragmentManager = fragment.childFragmentManager,
        lifecycle = fragment.lifecycle,
        diffCallback = diffCallback,
    )

    constructor(
        fragmentActivity: FragmentActivity,
        diffCallback: DiffUtil.ItemCallback<T>,
    ) : this(
        fragmentManager = fragmentActivity.supportFragmentManager,
        lifecycle = fragmentActivity.lifecycle,
        diffCallback = diffCallback,
    )


    override fun getItemCount(): Int = _differ.currentList.size

    protected fun getItem(position: Int): T = _differ.currentList[position]

    protected fun getItemOrNull(position: Int): T? = _differ.currentList.getOrNull(position)

    @JvmOverloads
    fun submitList(items: List<T>, commitCallback: Runnable? = null) {
        _differ.submitList(items, commitCallback)
    }

    fun addListListener(listener: ListListener<T>) {
        _differ.addListListener(listener)
    }

    fun removeListListener(listener: ListListener<T>) {
        _differ.removeListListener(listener)
    }


    protected open fun onCurrentListChanged(previousList: List<T>, currentList: List<T>) {}
}