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Infinite scroll for Android recycler view
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import android.support.v7.widget.LinearLayoutManager | |
import android.support.v7.widget.RecyclerView | |
import rx.Observable | |
import rx.Subscriber | |
/** | |
* Create infinite on scroll listener | |
* | |
* @param linearLayoutManager layout manager to be able to say when next loading is needed | |
* @return observeable to inform about needed next page loading | |
*/ | |
fun RecyclerView.onInfiniteLoading(linearLayoutManager: LinearLayoutManager): Observable<Int> { | |
val subscribers: MutableList<Subscriber<in Int>> = mutableListOf() | |
addOnScrollListener(InfiniteRecyclerOnScrollListener(linearLayoutManager, { page -> | |
subscribers.forEach { s -> s.onNext(page) } | |
})) | |
return Observable.create({ p -> subscribers.add(p) }) | |
} | |
/** | |
* Listener informs when another portion of data should be loaded what | |
* allows to provide infinite-scroll on UI lists | |
* | |
* @param linearLayoutManager layout manager to be able to say when next loading is needed | |
* @param onLoadMore logic for loading next page | |
* @param visibleThreshold the minimum number of items to have below current scroll position before loading more. | |
*/ | |
class InfiniteRecyclerOnScrollListener( | |
val linearLayoutManager: LinearLayoutManager, | |
val onLoadMore: (Int) -> Unit, | |
val visibleThreshold: Int = 5 | |
) : RecyclerView.OnScrollListener() { | |
private var previousTotal = 0 | |
private var loading = true | |
private var currentPage = 1 | |
override fun onScrolled(recyclerView: RecyclerView?, dx: Int, dy: Int) { | |
super.onScrolled(recyclerView, dx, dy) | |
val visibleItemCount = recyclerView!!.childCount | |
val totalItemCount = linearLayoutManager.itemCount | |
val firstVisibleItem = linearLayoutManager.findFirstVisibleItemPosition() | |
if (loading) { | |
if (totalItemCount > previousTotal) { | |
loading = false | |
previousTotal = totalItemCount | |
} | |
} | |
if (!loading && totalItemCount - visibleItemCount <= firstVisibleItem + visibleThreshold) { | |
currentPage++ | |
onLoadMore(currentPage) | |
loading = true | |
} | |
} | |
} |
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import android.content.Context | |
import android.support.v7.widget.RecyclerView | |
import android.view.View | |
import android.view.ViewGroup | |
/** | |
* Adapter for UI list | |
* @param viewFactory factory provide UI list items for view holder | |
* @param display decorator for displaying data on UI list item | |
* @param items current items in adapter (must be mutable due to android recycler view) | |
*/ | |
class ListAdapter<T, TU : View>( | |
val viewFactory: (Context) -> TU, | |
val display: (T?, ViewHolder<TU>) -> Unit, | |
val items: MutableList<T> = mutableListOf() | |
) | |
: RecyclerView.Adapter<ListAdapter.ViewHolder<TU>>() { | |
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder<TU> = ViewHolder(viewFactory(parent.context)) | |
override fun onBindViewHolder(holder: ViewHolder<TU>, position: Int) = display(items[position], holder) | |
override fun getItemCount(): Int = items.size | |
class ViewHolder<out TU : View>(val view: TU) : RecyclerView.ViewHolder(view) | |
fun add(t: T) { | |
items.add(t) | |
} | |
} |
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import android.support.v7.widget.LinearLayoutManager | |
import android.support.v7.widget.RecyclerView | |
class ResourcesActivity : AppCompatActivity() { | |
override fun onCreate(savedInstanceState: Bundle?) { | |
super.onCreate(savedInstanceState) | |
val listView: RecyclerView = findViewById(R.id.resource_list) as RecyclerView | |
val listAdapter = //create list adapter with proper factory and decorator | |
listView.adapter = listAdapter | |
val linearLayoutManager = LinearLayoutManager(this) | |
listView.layoutManager = linearLayoutManager | |
val generateItems: (Int) -> Unit = { page -> | |
(1 until 20).forEach { i -> | |
listAdapter.add(Resource("" + page + "-" + i + ".txt")) | |
} | |
listAdapter.notifyDataSetChanged() | |
} | |
listView.onInfiniteLoading(linearLayoutManager) | |
.subscribeOn(Schedulers.io()) | |
.observeOn(AndroidSchedulers.mainThread()) | |
.subscribe { page -> | |
info("[LazyLoading] NextPage: " + page) | |
generateItems(page) | |
} | |
generateItems(0) | |
} | |
} |
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