How to Pagination using retrofit to fetch next items from API on Scrolling in kotlin? - android-studio

Question

I want to make my recyclerview paginationscrolling using retrofit.
I already complete get Json data using retrofit. It means interface API is correct from API Document.
However, if I loaded more 20items. can not scroll more items in Client.
when I checked Server data. per one page can get maximum 20items.
For example, if I loaded 25items in my recyclerview.
page 0: 20, page 1: 5.
if I want scrolling all items, How can I make paginationscrolling for retrofit??
check some my code and help me..
Response
Interface API
#GET("/store/cart/mine")
fun getCart(#Header("Authorization") token: String?, #Query("page") page:Int): Call<CartResponse>
CartViewActivity
class CartViewActivity : AppCompatActivity(), SwipeRefreshLayout.OnRefreshListener {
private val lastVisibleItemPosition: Int
get()= LinearLayoutManager.HORIZONTAL
private lateinit var scrollListener: RecyclerView.OnScrollListener
lateinit var mAdapter: CartItemRecyclerAdapter
#RequiresApi(Build.VERSION_CODES.N)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_cart_view)
val page = 0
val token = SharedPreference.getTokenInfo(this)
Client.retrofitService.getCart(token,page).enqueue(object :Callback<CartResponse> {
override fun onResponse(call: Call<CartResponse>, response: Response<CartResponse>) {
if (response?.isSuccessful == true) {
swipeRefreshLo.setOnRefreshListener(this#CartViewActivity)
showdata(response.body()?.docs!!)
}else if(response?.isSuccessful==false) {
val er = Gson().fromJson(response.errorBody()?.charStream(), ErrorResponse::class.java)
if (er.code==60202) {
}
}
}
override fun onFailure(call: Call<CartResponse>, t: Throwable) {
}
})
}
private fun showdata(results: MutableList<cartDocs>) {
recycler_view.apply {
mAdapter=CartItemRecyclerAdapter(context,context as Activity, results)
recycler_view.adapter=mAdapter
recycler_view.layoutManager=LinearLayoutManager(context)
setRecyclerViewScrollListener()
}
}
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")
recyclerView.removeOnScrollListener(scrollListener)
}
}
}
}
override fun onRefresh() {
swipeRefreshLo.isRefreshing = false
}
}

Answer 1

Firstly, you need to modify your adapter to be able to update existing data, instead of creating new adapter every time you fetch new data.
Adapter should be initialised before getting the data, to be able to call methods on it.
You should create a method inside the adapter, something like
fun updateData(results: MutableList<cartDocs>) {
dataSet.addAll(results)
notifyItemRangeInserted(start, newItemsSize)
}
Then, we you get response from server in onSuccess() you should call method above, and increment page, so the next time you load data, you get new items.
Data should be fetched first time when screen loads (page will be 0), and then when user scrolls to bottom of RV ().