Endless scroll kotlin recycling view/ListView

Question

I am desperately trying to implement endless scrolling on an android app using kotlin. All the tutorials are either useless since they dont explain things properly. So for example: https://github.com/chetdeva/recyclerview-bindings

it looks promising but the author uses phrases like "put this in your BindingAdapter" so i look what this BindingAdapter is, I found a java file but if you insert anything in there I get errors. Its like anything I try fails directly.

The other tutorials are written in java and even with "translate to kotlin" option its useless since the translated code throws 100 errors.

I tried things like :

setContentView(R.layout.activity_main)
    list.layoutManager = LinearLayoutManager(this)
    list.hasFixedSize()
    list.adapter = ListAdapter(this, getLists())
    val list_view: RecyclerView = findViewById(R.id.list)
    fun setRecyclerViewScrollListener() {
        list_view.addOnScrollListener(object : RecyclerView.OnScrollListener() {
            override fun onScrolled(recyclerView: RecyclerView?, dx: Int, dy: Int) {
                val height = list_view.getHeight()

                val diff = height-dy
                if (diff < 1000){
                    /*load next list */
                }
            }
        })
    }
    setRecyclerViewScrollListener()
}

or this

val inflater = LayoutInflater.from(this@MainActivity)
val layout = inflater.inflate(R.layout.append_list, null, false)
button.setOnClickListener{screen.addView(layout)}

Is there a bullet proof method where you can simply append elemets like with html and js? I wrote this snippet in 2 min. Is there a similar "easy" way in Android/Kotlin?

$("#next").click(function(){
  $(".append_text").append("new text <img src='http://static.webshopapp.com/shops/015426/files/005031634/560x625x2/kek-amsterdam-wandtattoo-hase-forest-friends-braun.jpg'/>")
})

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button id="next">Load</button>

<span class="append_text"> </span>

In general I recive a lot of errors for choosing the wrong Layout. I tried Listview and contrainlayout and recycling Layout and Vertical Scrolling layout and so on. Is there a simple body tag where you can simply append a xml file?

I think I go the wrong way the whole time because I see everything though the eyes of a Web. Dev. while android does not have the classical DOM. Can anybody explain it to me with an minimal example on how to append a xml file to the main xml file on button click/on scroll?

score 12 · Answer 1 · edited Aug 24 '18 at 05:56

12

I use this method for adding endless scroll functionality to a recyclerview in Kotlin:

private fun setRecyclerViewScrollListener() {
    scrollListener = object : RecyclerView.OnScrollListener() {
        override fun onScrollStateChanged(recyclerView: RecyclerView?, newState: Int) {
            super.onScrollStateChanged(recyclerView, newState)
            val totalItemCount = recyclerView!!.layoutManager.itemCount
            if (totalItemCount == lastVisibleItemPosition + 1) {
                Log.d("MyTAG", "Load new list")
                recycler.removeOnScrollListener(scrollListener)
            }
        }
    }
    recycler.addOnScrollListener(scrollListener)
}

the variable lastVisibleItemPosition is declared as follows:

private val lastVisibleItemPosition: Int get() = linearLayoutManager.findLastVisibleItemPosition()

private lateinit var scrollListener: RecyclerView.OnScrollListener

Just call the setRecyclerViewScrollListener() method every time you nedd to add this functionality to the recyclerView.

Hope it helps,

Leonardo

edited Aug 24 '18 at 05:56

Vinu

156
2
9

answered Jan 22 '18 at 15:43

Leonardo Medori

341
2
9

where do you define these methods? If I add this into my MainAct. into the onCreate function, `get`, `linearLayoutManager`, `LOG_TAG`, `chatRecycler`, `recycler` and `scrollListener` are either undefined or cant be resolved. Where are the xml files? – hansTheFranz Jan 22 '18 at 20:08
@hansTheFranz I edited my code, sorry for the misprint, chatRecycler and recyler are the same RecyclerView, LOG_TAG is a string for logging purpose, I also added the declaration of scrollListener. linearLayoutManager is the layoutmanager you have to set to the recyclerview and get() is the getter for lastVisibleItemPosition variable. – Leonardo Medori Jan 23 '18 at 04:59
Thanks for this piece of code, @LeonardoMedori. Can I ask you why you have this next line in your code? `recycler.removeOnScrollListener(scrollListener)` – Rod Sep 13 '19 at 15:23
@Rod I remove the scrollListener and I add it again after I finished updating the list. If I don't remove the listener the onScrollStateChanged method is called many times and (totalItemCount == lastVisibleItemPosition + 1) condition can be true more than once. So instead of having a boolean for checking if the list is updated I remove the listener, make a call, update the list and than add the listener again. – Leonardo Medori Sep 18 '19 at 07:43

score 1 · Answer 2 · answered Aug 02 '20 at 13:30

1

set in recycler view in scroll listener

 recycler.addOnScrollListener(your listener)

answered Aug 02 '20 at 13:30

Endless scroll kotlin recycling view/ListView

2 Answers2