Merge pull request #530 from tzugen/diff

Use DiffUtil for better performance when refreshing the data..

core/domain/src/main/kotlin/org/moire/ultrasonic/domain/GenericEntry.kt

@@ -1,7 +1,19 @@
 package org.moire.ultrasonic.domain
 
 abstract class GenericEntry {
-    // TODO Should be non-null!
+    // TODO: Should be non-null!
     abstract val id: String?
     open val name: String? = null
+
+    // These are just a formality and will never be called,
+    // because Kotlin data classes will have autogenerated equals() and hashCode() functions
+    override operator fun equals(other: Any?): Boolean {
+        return this === other
+    }
+
+    override fun hashCode(): Int {
+        var result = id?.hashCode() ?: 0
+        result = 31 * result + (name?.hashCode() ?: 0)
+        return result
+    }
 }

ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/AlbumListFragment.kt

@@ -49,8 +49,9 @@ class AlbumListFragment : GenericListFragment<MusicDirectory.Entry, AlbumRowAdap
         if (args == null) throw IllegalArgumentException("Required arguments are missing")
 
         val refresh = args.getBoolean(Constants.INTENT_EXTRA_NAME_REFRESH)
+        val append = args.getBoolean(Constants.INTENT_EXTRA_NAME_APPEND)
 
-        return listModel.getAlbumList(refresh, refreshListView!!, args)
+        return listModel.getAlbumList(refresh or append, refreshListView!!, args)
     }
 
     /**

ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/AlbumListModel.kt

@@ -13,7 +13,8 @@ import org.moire.ultrasonic.util.Util
 
 class AlbumListModel(application: Application) : GenericListModel(application) {
 
-    val albumList: MutableLiveData<List<MusicDirectory.Entry>> = MutableLiveData()
+    val albumList: MutableLiveData<List<MusicDirectory.Entry>> = MutableLiveData(listOf())
+    var lastType: String? = null
     private var loadedUntil: Int = 0
 
     fun getAlbumList(
@@ -21,8 +22,14 @@ class AlbumListModel(application: Application) : GenericListModel(application) {
         swipe: SwipeRefreshLayout,
         args: Bundle
     ): LiveData<List<MusicDirectory.Entry>> {
+        // Don't reload the data if navigating back to the view that was active before.
+        // This way, we keep the scroll position
+        val albumListType = args.getString(Constants.INTENT_EXTRA_NAME_ALBUM_LIST_TYPE)!!
 
-        backgroundLoadFromServer(refresh, swipe, args)
+        if (refresh || albumList.value!!.isEmpty() || albumListType != lastType) {
+            lastType = albumListType
+            backgroundLoadFromServer(refresh, swipe, args)
+        }
         return albumList
     }
 

ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/ArtistListModel.kt

@@ -30,13 +30,17 @@ import org.moire.ultrasonic.service.MusicService
  * Provides ViewModel which contains the list of available Artists
  */
 class ArtistListModel(application: Application) : GenericListModel(application) {
-    private val artists: MutableLiveData<List<Artist>> = MutableLiveData()
+    private val artists: MutableLiveData<List<Artist>> = MutableLiveData(listOf())
 
     /**
      * Retrieves all available Artists in a LiveData
      */
     fun getItems(refresh: Boolean, swipe: SwipeRefreshLayout): LiveData<List<Artist>> {
-        backgroundLoadFromServer(refresh, swipe)
+        // Don't reload the data if navigating back to the view that was active before.
+        // This way, we keep the scroll position
+        if (artists.value!!.isEmpty() || refresh) {
+            backgroundLoadFromServer(refresh, swipe)
+        }
         return artists
     }
 

ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/GenericRowAdapter.kt

@@ -16,20 +16,24 @@ import android.widget.ImageView
 import android.widget.PopupMenu
 import android.widget.RelativeLayout
 import android.widget.TextView
+import androidx.recyclerview.widget.DiffUtil
+import androidx.recyclerview.widget.ListAdapter
 import androidx.recyclerview.widget.RecyclerView
 import org.moire.ultrasonic.R
 import org.moire.ultrasonic.data.ActiveServerProvider
+import org.moire.ultrasonic.domain.GenericEntry
 import org.moire.ultrasonic.domain.MusicFolder
 import org.moire.ultrasonic.view.SelectMusicFolderView
 
 /*
 * An abstract Adapter, which can be extended to display a List of <T> in a RecyclerView
 */
-abstract class GenericRowAdapter<T>(
+abstract class GenericRowAdapter<T : GenericEntry>(
     val onItemClick: (T) -> Unit,
     val onContextMenuClick: (MenuItem, T) -> Boolean,
     private val onMusicFolderUpdate: (String?) -> Unit
-) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
+) : ListAdapter<T, RecyclerView.ViewHolder>(GenericDiffCallback()) {
+
     open var itemList: List<T> = listOf()
     protected abstract val layout: Int
     protected abstract val contextMenuLayout: Int
@@ -40,11 +44,12 @@ abstract class GenericRowAdapter<T>(
     var selectedFolder: String? = null
 
     /**
-     * Sets the data to be displayed in the RecyclerView
+     * Sets the data to be displayed in the RecyclerView,
+     * using DiffUtil to efficiently calculate the minimum required changes..
      */
     open fun setData(data: List<T>) {
+        submitList(data)
         itemList = data
-        notifyDataSetChanged()
     }
 
     /**
@@ -136,5 +141,17 @@ abstract class GenericRowAdapter<T>(
     companion object {
         internal const val TYPE_HEADER = 0
         internal const val TYPE_ITEM = 1
+
+        /**
+         * Calculates the differences between data sets
+         */
+        class GenericDiffCallback<T : GenericEntry> : DiffUtil.ItemCallback<T>() {
+            override fun areContentsTheSame(oldItem: T, newItem: T): Boolean {
+                return oldItem == newItem
+            }
+            override fun areItemsTheSame(oldItem: T, newItem: T): Boolean {
+                return oldItem.id == newItem.id
+            }
+        }
     }
 }