fix: btnTop scroll didn't work in replies

app/src/main/java/com/github/libretube/ui/fragments/CommentsMainFragment.kt

@@ -4,6 +4,7 @@ import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.view.ViewTreeObserver
 import androidx.core.view.isVisible
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.activityViewModels
@@ -25,6 +26,8 @@ class CommentsMainFragment : Fragment() {
     private val binding get() = _binding!!
     private val viewModel: CommentsViewModel by activityViewModels()
 
+    private var scrollListener: ViewTreeObserver.OnScrollChangedListener? = null
+
     override fun onCreateView(
         inflater: LayoutInflater,
         container: ViewGroup?,
@@ -45,17 +48,19 @@ class CommentsMainFragment : Fragment() {
         val commentsSheet = parentFragment as? CommentsSheet
         commentsSheet?.binding?.btnScrollToTop?.setOnClickListener {
             // scroll back to the top / first comment
-            _binding?.commentsRV?.smoothScrollToPosition(0)
+            _binding?.commentsRV?.smoothScrollToPosition(POSITION_START)
-            viewModel.currentCommentsPosition = 0
+            viewModel.setCommentsPosition(POSITION_START)
         }
 
-        binding.commentsRV.viewTreeObserver.addOnScrollChangedListener {
+        scrollListener = ViewTreeObserver.OnScrollChangedListener {
             // save the last scroll position to become used next time when the sheet is opened
-            viewModel.currentCommentsPosition = layoutManager.findFirstVisibleItemPosition()
+            viewModel.setCommentsPosition(layoutManager.findFirstVisibleItemPosition())
-
             // hide or show the scroll to top button
-            commentsSheet?.binding?.btnScrollToTop?.isVisible = viewModel.currentCommentsPosition != 0
+            commentsSheet?.binding?.btnScrollToTop?.isVisible =
+                viewModel.currentCommentsPosition.value != 0
         }
+        binding.commentsRV.viewTreeObserver.addOnScrollChangedListener(scrollListener)
+
         commentsSheet?.updateFragmentInfo(false, getString(R.string.comments))
 
         val commentPagingAdapter = CommentPagingAdapter(
@@ -97,8 +102,18 @@ class CommentsMainFragment : Fragment() {
         }
     }
 
+    override fun onPause() {
+        super.onPause()
+        binding.commentsRV.viewTreeObserver.removeOnScrollChangedListener(scrollListener)
+        scrollListener = null
+    }
+
     override fun onDestroyView() {
         super.onDestroyView()
         _binding = null
     }
+
+    companion object {
+        private const val POSITION_START = 0
+    }
 }

app/src/main/java/com/github/libretube/ui/fragments/CommentsRepliesFragment.kt

@@ -4,6 +4,7 @@ import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.view.ViewTreeObserver
 import androidx.core.view.isGone
 import androidx.core.view.isVisible
 import androidx.core.view.updatePadding
@@ -31,6 +32,8 @@ class CommentsRepliesFragment : Fragment() {
 
     private val viewModel: CommentsViewModel by activityViewModels()
 
+    private var scrollListener: ViewTreeObserver.OnScrollChangedListener? = null
+
     override fun onCreateView(
         inflater: LayoutInflater,
         container: ViewGroup?,
@@ -66,9 +69,37 @@ class CommentsRepliesFragment : Fragment() {
         )
 
         binding.commentsRV.updatePadding(top = 0)
-        binding.commentsRV.layoutManager = LinearLayoutManager(context)
+
+        val layoutManager = LinearLayoutManager(context)
+        binding.commentsRV.layoutManager = layoutManager
+
         binding.commentsRV.adapter = repliesAdapter
 
+        // init scroll position
+        if (viewModel.currentRepliesPosition.value != null) {
+            if (viewModel.currentRepliesPosition.value!! > POSITION_START) {
+                layoutManager.scrollToPosition(viewModel.currentRepliesPosition.value!!)
+            } else {
+                layoutManager.scrollToPosition(POSITION_START)
+            }
+        }
+
+        commentsSheet?.binding?.btnScrollToTop?.setOnClickListener {
+            // scroll back to the top / first comment
+            layoutManager.scrollToPosition(POSITION_START)
+            viewModel.setRepliesPosition(POSITION_START)
+        }
+
+        scrollListener = ViewTreeObserver.OnScrollChangedListener {
+            // save the last scroll position to become used next time when the sheet is opened
+            viewModel.setRepliesPosition(layoutManager.findFirstVisibleItemPosition())
+            // hide or show the scroll to top button
+            commentsSheet?.binding?.btnScrollToTop?.isVisible =
+                viewModel.currentRepliesPosition.value != 0
+        }
+
+        binding.commentsRV.viewTreeObserver.addOnScrollChangedListener(scrollListener)
+
         viewModel.selectedCommentLiveData.postValue(comment.repliesPage)
 
         viewLifecycleOwner.lifecycleScope.launch {
@@ -88,8 +119,18 @@ class CommentsRepliesFragment : Fragment() {
         }
     }
 
+    override fun onPause() {
+        super.onPause()
+        binding.commentsRV.viewTreeObserver.removeOnScrollChangedListener(scrollListener)
+        scrollListener = null
+    }
+
     override fun onDestroyView() {
         super.onDestroyView()
         _binding = null
     }
+
+    companion object {
+        const val POSITION_START = 0
+    }
 }

app/src/main/java/com/github/libretube/ui/models/CommentsViewModel.kt

@@ -1,5 +1,6 @@
 package com.github.libretube.ui.models
 
+import androidx.lifecycle.LiveData
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.asFlow
@@ -41,7 +42,12 @@ class CommentsViewModel : ViewModel() {
     var channelAvatar: String? = null
     var handleLink: ((url: String) -> Unit)? = null
 
-    var currentCommentsPosition = 0
+    private val _currentCommentsPosition = MutableLiveData(0)
+    val currentCommentsPosition: LiveData<Int> = _currentCommentsPosition
+
+    private val _currentRepliesPosition = MutableLiveData(0)
+    val currentRepliesPosition: LiveData<Int> = _currentRepliesPosition
+
     var commentsSheetDismiss: (() -> Unit)? = null
 
     fun setCommentSheetExpand(value: Boolean?) {
@@ -52,6 +58,18 @@ class CommentsViewModel : ViewModel() {
 
     fun reset() {
         setCommentSheetExpand(null)
-        currentCommentsPosition = 0
+        _currentCommentsPosition.value = 0
+    }
+
+    fun setCommentsPosition(position: Int) {
+        if (position != currentCommentsPosition.value) {
+            _currentCommentsPosition.postValue(position)
+        }
+    }
+
+    fun setRepliesPosition(position: Int) {
+        if (position != currentRepliesPosition.value) {
+            _currentRepliesPosition.postValue(position)
+        }
     }
 }