part 7: adding infinite scroll and updating news manager to allow pag…

…ination

app/src/main/java/com/droidcba/kedditbysteps/commons/InfiniteScrollListener.kt

@@ -0,0 +1,42 @@
+package com.droidcba.kedditbysteps.commons
+
+import android.support.v7.widget.LinearLayoutManager
+import android.support.v7.widget.RecyclerView
+import android.util.Log
+
+class InfiniteScrollListener(
+        val func: () -> Unit,
+        val layoutManager: LinearLayoutManager) : RecyclerView.OnScrollListener() {
+
+    private var previousTotal = 0
+    private var loading = true
+    private var visibleThreshold = 2
+    private var firstVisibleItem = 0
+    private var visibleItemCount = 0
+    private var totalItemCount = 0
+
+    override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
+        super.onScrolled(recyclerView, dx, dy)
+
+        if (dy > 0) {
+            visibleItemCount = recyclerView.childCount;
+            totalItemCount = layoutManager.itemCount;
+            firstVisibleItem = layoutManager.findFirstVisibleItemPosition();
+
+            if (loading) {
+                if (totalItemCount > previousTotal) {
+                    loading = false;
+                    previousTotal = totalItemCount;
+                }
+            }
+            if (!loading && (totalItemCount - visibleItemCount)
+                    <= (firstVisibleItem + visibleThreshold)) {
+                // End has been reached
+                Log.i("InfiniteScrollListener", "End reached");
+                func()
+                loading = true;
+            }
+        }
+    }
+
+}

app/src/main/java/com/droidcba/kedditbysteps/commons/Models.kt

@@ -3,6 +3,11 @@ package com.droidcba.kedditbysteps.commons
 import com.droidcba.kedditbysteps.commons.adapter.AdapterConstants
 import com.droidcba.kedditbysteps.commons.adapter.ViewType
 
+data class RedditNews(
+        val after: String,
+        val before: String,
+        val news: List<RedditNewsItem>)
+
 data class RedditNewsItem(
         val author: String,
         val title: String,

app/src/main/java/com/droidcba/kedditbysteps/features/news/NewsFragment.kt

@@ -7,6 +7,8 @@ import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import com.droidcba.kedditbysteps.R
+import com.droidcba.kedditbysteps.commons.InfiniteScrollListener
+import com.droidcba.kedditbysteps.commons.RedditNews
 import com.droidcba.kedditbysteps.commons.RxBaseFragment
 import com.droidcba.kedditbysteps.commons.extensions.inflate
 import com.droidcba.kedditbysteps.features.news.adapter.NewsAdapter
@@ -15,6 +17,7 @@ import rx.schedulers.Schedulers
 
 class NewsFragment : RxBaseFragment() {
 
+    private var redditNews: RedditNews? = null
     private val newsManager by lazy { NewsManager() }
 
     override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
@@ -25,7 +28,10 @@ class NewsFragment : RxBaseFragment() {
         super.onActivityCreated(savedInstanceState)
 
         news_list.setHasFixedSize(true)
-        news_list.layoutManager = LinearLayoutManager(context)
+        val linearLayout = LinearLayoutManager(context)
+        news_list.layoutManager = linearLayout
+        news_list.clearOnScrollListeners()
+        news_list.addOnScrollListener(InfiniteScrollListener({ requestNews() }, linearLayout))
         initAdapter()
 
         if (savedInstanceState == null) {
@@ -34,11 +40,17 @@ class NewsFragment : RxBaseFragment() {
     }
 
     private fun requestNews() {
-        val subscription = newsManager.getNews()
+        /**
+         * first time will send empty string for after parameter.
+         * Next time we will have redditNews set with the next page to
+         * navigate with the after param.
+         */
+        val subscription = newsManager.getNews(redditNews?.after ?: "")
                 .subscribeOn(Schedulers.io())
                 .subscribe (
                         { retrievedNews ->
-                            (news_list.adapter as NewsAdapter).addNews(retrievedNews)
+                            redditNews = retrievedNews
+                            (news_list.adapter as NewsAdapter).addNews(retrievedNews.news)
                         },
                         { e ->
                             Snackbar.make(news_list, e.message ?: "", Snackbar.LENGTH_LONG).show()

app/src/main/java/com/droidcba/kedditbysteps/features/news/NewsManager.kt

@@ -1,29 +1,43 @@
 package com.droidcba.kedditbysteps.features.news
 
 import com.droidcba.kedditbysteps.api.RestAPI
+import com.droidcba.kedditbysteps.commons.RedditNews
 import com.droidcba.kedditbysteps.commons.RedditNewsItem
 import rx.Observable
 
 /**
- * News Manager allows you to request more news from Reddit.
+ * News Manager allows you to request news from Reddit API.
  *
  * @author juancho
  */
 class NewsManager(private val api: RestAPI = RestAPI()) {
 
-    fun getNews(limit: String = "10"): Observable<List<RedditNewsItem>> {
+    /**
+     *
+     * Returns Reddit News paginated by the given limit.
+     *
+     * @param after indicates the next page to navigate.
+     * @param limit the number of news to request.
+     */
+    fun getNews(after: String, limit: String = "10"): Observable<RedditNews> {
         return Observable.create {
             subscriber ->
-            val callResponse = api.getNews("", limit)
+            val callResponse = api.getNews(after, limit)
             val response = callResponse.execute()
 
             if (response.isSuccessful) {
-                val news = response.body().data.children.map {
+                val dataResponse = response.body().data
+                val news = dataResponse.children.map {
                     val item = it.data
                     RedditNewsItem(item.author, item.title, item.num_comments,
                             item.created, item.thumbnail, item.url)
                 }
-                subscriber.onNext(news)
+                val redditNews = RedditNews(
+                        dataResponse.after ?: "",
+                        dataResponse.before ?: "",
+                        news)
+
+                subscriber.onNext(redditNews)
                 subscriber.onCompleted()
             } else {
                 subscriber.onError(Throwable(response.message()))