From 798e16eab033d90baf966e74888a52a7acee9cee Mon Sep 17 00:00:00 2001
From: Syer10 <syer10@users.noreply.github.com>
Date: Fri, 28 May 2021 19:06:20 -0400
Subject: [PATCH] Save the scroll state for sources

---
 .../ca/gosyer/ui/sources/SourcesMenu.kt       | 11 +++++----
 .../ui/sources/components/SourceScreen.kt     | 13 +++++-----
 .../kotlin/ca/gosyer/util/compose/State.kt    | 24 +++++++++++++++++++
 3 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/src/main/kotlin/ca/gosyer/ui/sources/SourcesMenu.kt b/src/main/kotlin/ca/gosyer/ui/sources/SourcesMenu.kt
index 0da25636..b62b919e 100644
--- a/src/main/kotlin/ca/gosyer/ui/sources/SourcesMenu.kt
+++ b/src/main/kotlin/ca/gosyer/ui/sources/SourcesMenu.kt
@@ -33,6 +33,7 @@ import ca.gosyer.ui.sources.components.SourceHomeScreen
 import ca.gosyer.ui.sources.components.SourceScreen
 import ca.gosyer.util.compose.ThemedWindow
 import com.github.zsoltk.compose.savedinstancestate.Bundle
+import com.github.zsoltk.compose.savedinstancestate.BundleScope
 import com.github.zsoltk.compose.savedinstancestate.LocalSavedInstanceState
 
 fun openSourcesMenu() {
@@ -85,10 +86,12 @@ fun SourcesMenu(bundle: Bundle, onMangaClick: (Long) -> Unit) {
                 }
 
                 val selectedSource: Source? = selectedSourceTab
-                if (selectedSource != null) {
-                    SourceScreen(selectedSource, onMangaClick)
-                } else {
-                    SourceHomeScreen(isLoading, sources, serverUrl, vm::addTab)
+                BundleScope(selectedSource?.id.toString(), autoDispose = false) {
+                    if (selectedSource != null) {
+                        SourceScreen(selectedSource, onMangaClick)
+                    } else {
+                        SourceHomeScreen(isLoading, sources, serverUrl, vm::addTab)
+                    }
                 }
             }
         }
diff --git a/src/main/kotlin/ca/gosyer/ui/sources/components/SourceScreen.kt b/src/main/kotlin/ca/gosyer/ui/sources/components/SourceScreen.kt
index b4fd8090..ebfe5663 100644
--- a/src/main/kotlin/ca/gosyer/ui/sources/components/SourceScreen.kt
+++ b/src/main/kotlin/ca/gosyer/ui/sources/components/SourceScreen.kt
@@ -26,6 +26,7 @@ import ca.gosyer.data.models.Source
 import ca.gosyer.ui.base.components.LoadingScreen
 import ca.gosyer.ui.base.components.MangaGridItem
 import ca.gosyer.ui.base.vm.viewModel
+import ca.gosyer.util.compose.persistentLazyListState
 import com.github.zsoltk.compose.savedinstancestate.Bundle
 import com.github.zsoltk.compose.savedinstancestate.LocalSavedInstanceState
 
@@ -34,13 +35,8 @@ fun SourceScreen(
     source: Source,
     onMangaClick: (Long) -> Unit
 ) {
-    val upstream = LocalSavedInstanceState.current
-
+    val bundle = LocalSavedInstanceState.current
     val vm = viewModel<SourceScreenViewModel>()
-    val bundle = remember(source.id) {
-        upstream.getBundle(source.id.toString())
-            ?: Bundle().also { upstream.putBundle(source.id.toString(), it) }
-    }
     remember(source.id) {
         vm.init(source, bundle)
     }
@@ -51,6 +47,7 @@ fun SourceScreen(
     val serverUrl by vm.serverUrl.collectAsState()
 
     MangaTable(
+        bundle,
         mangas,
         loading,
         hasNextPage,
@@ -64,6 +61,7 @@ fun SourceScreen(
 
 @Composable
 private fun MangaTable(
+    bundle: Bundle,
     mangas: List<Manga>,
     isLoading: Boolean = false,
     hasNextPage: Boolean = false,
@@ -95,7 +93,8 @@ private fun MangaTable(
                 }
             }
 
-            LazyVerticalGrid(GridCells.Adaptive(160.dp)) {
+            val persistentState = persistentLazyListState(bundle)
+            LazyVerticalGrid(GridCells.Adaptive(160.dp), state = persistentState) {
                 items(mangas) { manga ->
                     MangaGridItem(
                         title = manga.title,
diff --git a/src/main/kotlin/ca/gosyer/util/compose/State.kt b/src/main/kotlin/ca/gosyer/util/compose/State.kt
index 9920eb8f..77af242c 100644
--- a/src/main/kotlin/ca/gosyer/util/compose/State.kt
+++ b/src/main/kotlin/ca/gosyer/util/compose/State.kt
@@ -6,11 +6,35 @@
 
 package ca.gosyer.util.compose
 
+import androidx.compose.foundation.lazy.LazyListState
+import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.State
+import androidx.compose.runtime.remember
+import com.github.zsoltk.compose.savedinstancestate.Bundle
 import com.github.zsoltk.compose.savedinstancestate.LocalSavedInstanceState
 
 @Composable
 fun <T> State<T>.persistent(key: String) {
     val bundle = LocalSavedInstanceState.current
 }
+
+const val LAZY_LIST_ITEM = "lazy_list_item"
+const val LAZY_LIST_OFFSET = "lazy_list_offset"
+
+@Composable
+fun persistentLazyListState(bundle: Bundle = LocalSavedInstanceState.current): LazyListState {
+    val state = rememberLazyListState(
+        remember { bundle.getInt(LAZY_LIST_ITEM, 0) },
+        remember { bundle.getInt(LAZY_LIST_OFFSET, 0) }
+    )
+    DisposableEffect(Unit) {
+        onDispose {
+            bundle.putInt(LAZY_LIST_ITEM, state.firstVisibleItemIndex)
+            bundle.putInt(LAZY_LIST_OFFSET, state.firstVisibleItemScrollOffset)
+        }
+    }
+
+    return state
+}