From bc16b64be431a6600036ef2757f140f12bd8b3c4 Mon Sep 17 00:00:00 2001
From: tzugen <tzugen@riseup.net>
Date: Mon, 21 Jun 2021 13:41:39 +0200
Subject: [PATCH] Avoid unnecessary reloads when navigating back, this
 preserves the scroll position.

---
 .../moire/ultrasonic/fragment/AlbumListFragment.kt    |  3 ++-
 .../org/moire/ultrasonic/fragment/AlbumListModel.kt   | 11 +++++++++--
 .../org/moire/ultrasonic/fragment/ArtistListModel.kt  |  8 ++++++--
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/AlbumListFragment.kt b/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/AlbumListFragment.kt
index 75b93057..97285d68 100644
--- a/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/AlbumListFragment.kt
+++ b/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)
     }
 
     /**
diff --git a/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/AlbumListModel.kt b/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/AlbumListModel.kt
index 5a6e1ba8..31ae714e 100644
--- a/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/AlbumListModel.kt
+++ b/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
     }
 
diff --git a/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/ArtistListModel.kt b/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/ArtistListModel.kt
index d58e97ca..a774ebcd 100644
--- a/ultrasonic/src/main/kotlin/org/moire/ultrasonic/fragment/ArtistListModel.kt
+++ b/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
     }