Add LoadMoreScrollListener.kt

app/src/main/java/chat/rocket/android/helper/LoadMoreScrollListener.kt

+package chat.rocket.android.helper
+
+import android.support.v7.widget.LinearLayoutManager
+import android.support.v7.widget.RecyclerView
+
+abstract class LoadMoreScrollListener(private val layoutManager: LinearLayoutManager, private val visibleThreshold: Int) : RecyclerView.OnScrollListener() {
+    private var isLoading: Boolean = false
+
+    override fun onScrolled(recyclerView: RecyclerView, deltaX: Int, deltaY: Int) {
+        super.onScrolled(recyclerView, deltaX, deltaY)
+
+        val visibleItemCount = recyclerView.childCount
+        val totalItemCount = layoutManager.itemCount
+        val firstVisibleItem = layoutManager.findFirstVisibleItemPosition()
+
+        if (!isLoading
+                && (firstVisibleItem + visibleItemCount) >= (totalItemCount - visibleThreshold)
+                && visibleItemCount < totalItemCount
+                && deltaY < 0) {
+            isLoading = true
+            requestMoreItem()
+        }
+    }
+
+    fun setLoadingDone() {
+        isLoading = false
+    }
+
+    abstract fun requestMoreItem()
+}
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