From 941dde341eb11703eadae543f351c9284617541c Mon Sep 17 00:00:00 2001
From: perokhe <81130286+perokhe@users.noreply.github.com>
Date: Thu, 27 Mar 2025 08:25:25 -0600
Subject: [PATCH] Fix next chapter button occasionally jumping to the last page
 of the current chapter (#1920)

---
 CHANGELOG.md                                  |  1 +
 .../ui/reader/viewer/pager/PagerViewer.kt     | 33 +++++++++++--------
 2 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3efc2ed27..ef67c5aaa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ The format is a modified version of [Keep a Changelog](https://keepachangelog.co
 
 ### Fixes
 - Fix Bangumi search results including novels ([@MajorTanya](https://github.com/MajorTanya)) ([#1885](https://github.com/mihonapp/mihon/pull/1885))
+- Fix next chapter button occasionally jumping to the last page of the current chapter ([@perokhe](https://github.com/perokhe)) ([#1920](https://github.com/mihonapp/mihon/pull/1920))
 
 ## [v0.18.0] - 2025-03-20
 ### Added
diff --git a/app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewer.kt b/app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewer.kt
index ffa38bfba..cdd92a9f1 100644
--- a/app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewer.kt
+++ b/app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewer.kt
@@ -80,6 +80,19 @@ abstract class PagerViewer(val activity: ReaderActivity) : Viewer {
             }
         }
 
+    private val pagerListener = object : ViewPager.SimpleOnPageChangeListener() {
+        override fun onPageSelected(position: Int) {
+            if (!activity.isScrollingThroughPages) {
+                activity.hideMenu()
+            }
+            onPageChange(position)
+        }
+
+        override fun onPageScrollStateChanged(state: Int) {
+            isIdle = state == ViewPager.SCROLL_STATE_IDLE
+        }
+    }
+
     init {
         pager.isVisible = false // Don't layout the pager yet
         pager.layoutParams = LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT)
@@ -87,20 +100,7 @@ abstract class PagerViewer(val activity: ReaderActivity) : Viewer {
         pager.offscreenPageLimit = 1
         pager.id = R.id.reader_pager
         pager.adapter = adapter
-        pager.addOnPageChangeListener(
-            object : ViewPager.SimpleOnPageChangeListener() {
-                override fun onPageSelected(position: Int) {
-                    if (!activity.isScrollingThroughPages) {
-                        activity.hideMenu()
-                    }
-                    onPageChange(position)
-                }
-
-                override fun onPageScrollStateChanged(state: Int) {
-                    isIdle = state == ViewPager.SCROLL_STATE_IDLE
-                }
-            },
-        )
+        pager.addOnPageChangeListener(pagerListener)
         pager.tapListener = { event ->
             val viewPosition = IntArray(2)
             pager.getLocationOnScreen(viewPosition)
@@ -275,6 +275,9 @@ abstract class PagerViewer(val activity: ReaderActivity) : Viewer {
      * Sets the active [chapters] on this pager.
      */
     private fun setChaptersInternal(chapters: ViewerChapters) {
+        // Remove listener so the change in item doesn't trigger it
+        pager.removeOnPageChangeListener(pagerListener)
+
         val forceTransition = config.alwaysShowChapterTransition ||
             adapter.items.getOrNull(pager.currentItem) is ChapterTransition
         adapter.setChapters(chapters, forceTransition)
@@ -286,6 +289,8 @@ abstract class PagerViewer(val activity: ReaderActivity) : Viewer {
             moveToPage(pages[min(chapters.currChapter.requestedPage, pages.lastIndex)])
             pager.isVisible = true
         }
+
+        pager.addOnPageChangeListener(pagerListener)
     }
 
     /**