Can you use paging library and PagedList with a ViewPager?

Question

I'd like to use a ViewPager with paging library and PagedList. Is there a way to do this? If yes then what adapter should I use?

Right now I use FragmentStatePagerAdapter with a full list of items. I'd like to load pages of items on demand instead of loading all the data at once.

Answer 1

This is what I'm currently playing with. I've seen it paging, but I need to write some tests to ensure this is actually offering any benefits. Still a lot of room for improvements, but I think this is the core necessary for it to function.

This requires that you .setInitialLoadKey on the PageList. I wasn't able to get it to respond to something like .smoothScrollToPosition. It's working in an image viewer atm.

abstract class PagedListPagerAdapter<T>(fm: FragmentManager)
    : FragmentStatePagerAdapter(fm) {

    var pagedList: PagedList<T>? = null
        private set
    private var callback = PagerCallback()

    override fun getCount() = pagedList?.size ?: 0

    abstract fun createItem(position: Int): Fragment

    abstract var isSmoothScroll: Boolean

    override fun getItem(position: Int): Fragment {
        pagedList?.loadAround(position)
        return createItem(position)
    }

    fun getValue(position: Int): T? {
        return pagedList?.get(position)
    }

    fun submitList(pagedList: PagedList<T>?) {
        this.pagedList?.removeWeakCallback(callback)
        this.pagedList = pagedList
        this.pagedList?.addWeakCallback(null, callback)
        notifyDataSetChanged()
    }

    private inner class PagerCallback : PagedList.Callback() {
        override fun onChanged(position: Int, count: Int) = notifyDataSetChanged()
        override fun onInserted(position: Int, count: Int) = notifyDataSetChanged()
        override fun onRemoved(position: Int, count: Int) = notifyDataSetChanged()
    }
}

class ViewerAdapter(fm: FragmentManager)
    : PagedListPagerAdapter<ImageInfo>(fm) {

    override var isSmoothScroll = false

    override fun createItem(position: Int): Fragment {
        val fragment = ViewPagerFragment()
        fragment.source = getValue(position)
        return fragment
    }
}