resolves #99

app/src/main/java/xyz/quaver/pupil/adapters/ThumbnailPageAdapter.kt

@@ -0,0 +1,50 @@
+/*
+ *     Pupil, Hitomi.la viewer for Android
+ *     Copyright (C) 2020  tom5079
+ *
+ *     This program is free software: you can redistribute it and/or modify
+ *     it under the terms of the GNU General Public License as published by
+ *     the Free Software Foundation, either version 3 of the License, or
+ *     (at your option) any later version.
+ *
+ *     This program is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *     GNU General Public License for more details.
+ *
+ *     You should have received a copy of the GNU General Public License
+ *     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package xyz.quaver.pupil.adapters
+
+import android.view.ViewGroup
+import androidx.recyclerview.widget.GridLayoutManager
+import androidx.recyclerview.widget.RecyclerView
+import com.bumptech.glide.RequestManager
+import kotlin.math.min
+
+class ThumbnailPageAdapter(private val glide: RequestManager, private val thumbnails: List<String>) : RecyclerView.Adapter<ThumbnailPageAdapter.ViewHolder>() {
+
+    class ViewHolder(val view: RecyclerView) : RecyclerView.ViewHolder(view)
+
+    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
+        return ViewHolder(RecyclerView(parent.context).apply {
+            layoutManager = GridLayoutManager(parent.context, 3)
+            adapter = ThumbnailAdapter(glide, listOf())
+            layoutParams = ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT)
+        })
+    }
+
+    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
+        (holder.view.adapter as ThumbnailAdapter).apply {
+            thumbnails = this@ThumbnailPageAdapter.thumbnails.slice(9*position until min(9*position+9, this@ThumbnailPageAdapter.thumbnails.size))
+            notifyDataSetChanged()
+
+            holder.view.layoutManager?.scrollToPosition(itemCount-1)
+        }
+    }
+
+    override fun getItemCount() = if (thumbnails.isEmpty()) 0 else thumbnails.size/9 + if (thumbnails.size%9 != 0) 1 else 0
+
+}