Fix media viewer rail items jumping around while paging.

app/src/main/java/org/thoughtcrime/securesms/mediapreview/MediaPreviewV2Fragment.kt

@@ -165,11 +165,14 @@ class MediaPreviewV2Fragment : LoggingFragment(R.layout.fragment_media_preview_v
         { media -> jumpViewPagerToMedia(media) },
         object : ImageLoadingListener() {
           override fun onAllRequestsFinished() {
-            crossfadeViewIn(this@apply)
+            val willAnimateIn = crossfadeViewIn(this@apply)
+            if (!willAnimateIn) {
+              visible = true
+            }
           }
         }
       )
-      this.adapter = albumRailAdapter
+      adapter = albumRailAdapter
     }
   }
 
@@ -303,41 +306,30 @@ class MediaPreviewV2Fragment : LoggingFragment(R.layout.fragment_media_preview_v
   private fun bindAlbumRail(albumThumbnailMedia: List<Media>, currentItem: MediaTable.MediaRecord) {
     val albumRail: RecyclerView = binding.mediaPreviewPlaybackControls.recyclerView
     if (albumThumbnailMedia.size > 1) {
-      val albumPosition = albumThumbnailMedia.indexOfFirst { it.uri == currentItem.attachment?.uri }
       if (albumRail.visibility == GONE) {
         albumRail.visibility = View.INVISIBLE
       }
-
-      albumRailAdapter.currentItemPosition = albumPosition
-      albumRailAdapter.submitList(albumThumbnailMedia)
-      scrollAlbumRailToCurrentAdapterPosition()
+      val railItems = albumThumbnailMedia.map { MediaRailAdapter.MediaRailItem(it, it.uri == currentItem.attachment?.uri) }
+      albumRailAdapter.submitList(railItems) { albumRail.post { scrollAlbumRailToCurrentAdapterPosition() } }
     } else {
       albumRail.visibility = View.GONE
       albumRailAdapter.submitList(emptyList())
-      albumRailAdapter.imageLoadingListener.reset()
     }
   }
 
   private fun scrollAlbumRailToCurrentAdapterPosition() {
-    val currentItemPosition = albumRailAdapter.currentItemPosition
-    val currentList = albumRailAdapter.currentList
+    val currentItemPosition = albumRailAdapter.findSelectedItemPosition()
     val albumRail: RecyclerView = binding.mediaPreviewPlaybackControls.recyclerView
     albumRail.scrollToPosition(currentItemPosition)
-    for (i in currentList.indices) {
-      val isSelected = i == currentItemPosition
-      val stableId = albumRailAdapter.getItemId(i)
-      val viewHolder = albumRail.findViewHolderForItemId(stableId) as? MediaRailAdapter.MediaRailViewHolder
-      viewHolder?.setSelectedItem(isSelected)
-    }
     val offsetFromStart = (albumRail.width - individualItemWidth) / 2
     val smoothScroller = OffsetSmoothScroller(requireContext(), offsetFromStart)
     smoothScroller.targetPosition = currentItemPosition
     val layoutManager = albumRail.layoutManager as LinearLayoutManager
     layoutManager.startSmoothScroll(smoothScroller)
   }
 
-  private fun crossfadeViewIn(view: View, duration: Long = 200) {
-    if (!view.isVisible && !fullscreenHelper.isSystemUiVisible) {
+  private fun crossfadeViewIn(view: View, duration: Long = 200): Boolean {
+    return if (!view.isVisible && !fullscreenHelper.isSystemUiVisible) {
       val viewPropertyAnimator = view.animate()
         .alpha(1f)
         .setDuration(duration)
@@ -353,6 +345,9 @@ class MediaPreviewV2Fragment : LoggingFragment(R.layout.fragment_media_preview_v
         viewPropertyAnimator.interpolator = PathInterpolator(0.17f, 0.17f, 0f, 1f)
       }
       viewPropertyAnimator.start()
+      true
+    } else {
+      false
     }
   }
 

app/src/main/java/org/thoughtcrime/securesms/mediapreview/mediarail/MediaRailAdapter.kt

@@ -1,12 +1,8 @@
 package org.thoughtcrime.securesms.mediapreview.mediarail
 
 import android.graphics.drawable.Drawable
-import android.view.LayoutInflater
 import android.view.View
-import android.view.ViewGroup
 import android.widget.ImageView
-import androidx.recyclerview.widget.DiffUtil
-import androidx.recyclerview.widget.ListAdapter
 import androidx.recyclerview.widget.RecyclerView
 import com.bumptech.glide.load.DataSource
 import com.bumptech.glide.load.engine.GlideException
@@ -16,45 +12,59 @@ import org.thoughtcrime.securesms.R
 import org.thoughtcrime.securesms.components.ThumbnailView
 import org.thoughtcrime.securesms.mediasend.Media
 import org.thoughtcrime.securesms.mms.GlideRequests
-import org.thoughtcrime.securesms.util.adapter.StableIdGenerator
+import org.thoughtcrime.securesms.util.adapter.mapping.MappingAdapter
+import org.thoughtcrime.securesms.util.adapter.mapping.MappingModel
+import org.thoughtcrime.securesms.util.adapter.mapping.MappingViewHolder
 import org.thoughtcrime.securesms.util.visible
 import java.util.concurrent.atomic.AtomicInteger
 
 /**
  * This is the RecyclerView.Adapter for the row of thumbnails present in the media viewer screen.
  */
-class MediaRailAdapter(private val glideRequests: GlideRequests, listener: RailItemListener, imageLoadingListener: ImageLoadingListener) : ListAdapter<Media, MediaRailAdapter.MediaRailViewHolder>(MediaDiffer()) {
-  val imageLoadingListener: ImageLoadingListener
-
-  var currentItemPosition: Int = -1
-
-  private val listener: RailItemListener
-  private val stableIdGenerator: StableIdGenerator<Media>
+class MediaRailAdapter(
+  private val glideRequests: GlideRequests,
+  private val onRailItemSelected: (Media) -> Unit,
+  private val imageLoadingListener: ImageLoadingListener
+) : MappingAdapter() {
 
   init {
-    this.listener = listener
-    stableIdGenerator = StableIdGenerator()
-    this.imageLoadingListener = imageLoadingListener
-    setHasStableIds(true)
+    registerFactory(MediaRailItem::class.java, ::MediaRailViewHolder, R.layout.mediarail_media_item)
   }
 
-  override fun onCreateViewHolder(viewGroup: ViewGroup, type: Int): MediaRailViewHolder {
-    return MediaRailViewHolder(LayoutInflater.from(viewGroup.context).inflate(R.layout.mediarail_media_item, viewGroup, false))
+  override fun onAttachedToRecyclerView(recyclerView: RecyclerView) {
+    super.onAttachedToRecyclerView(recyclerView)
+    recyclerView.itemAnimator = null
+  }
+
+  override fun submitList(list: List<MappingModel<*>>?) {
+    super.submitList(list)
+    if (list?.isEmpty() == true) {
+      imageLoadingListener.reset()
+    }
   }
 
-  override fun onBindViewHolder(viewHolder: MediaRailViewHolder, i: Int) {
-    viewHolder.bind(getItem(i), i == currentItemPosition, glideRequests, listener, imageLoadingListener)
+  override fun submitList(list: List<MappingModel<*>>?, commitCallback: Runnable?) {
+    super.submitList(list, commitCallback)
+    if (list?.isEmpty() == true) {
+      imageLoadingListener.reset()
+    }
   }
 
-  override fun onViewRecycled(holder: MediaRailViewHolder) {
-    holder.recycle()
+  fun findSelectedItemPosition(): Int {
+    return indexOfFirst(MediaRailItem::class.java) { it.isSelected }.coerceAtLeast(0)
   }
 
-  override fun getItemId(position: Int): Long {
-    return stableIdGenerator.getId(getItem(position))
+  data class MediaRailItem(val media: Media, val isSelected: Boolean) : MappingModel<MediaRailItem> {
+    override fun areItemsTheSame(newItem: MediaRailItem): Boolean {
+      return media.uri == newItem.media.uri
+    }
+
+    override fun areContentsTheSame(newItem: MediaRailItem): Boolean {
+      return this == newItem
+    }
   }
 
-  class MediaRailViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
+  private inner class MediaRailViewHolder(itemView: View) : MappingViewHolder<MediaRailItem>(itemView) {
     private val image: ThumbnailView
     private val outline: View
     private val captionIndicator: View
@@ -67,36 +77,17 @@ class MediaRailAdapter(private val glideRequests: GlideRequests, listener: RailI
       overlay = itemView.findViewById(R.id.rail_item_overlay)
     }
 
-    fun bind(
-      media: Media,
-      isCurrentlySelected: Boolean,
-      glideRequests: GlideRequests,
-      railItemListener: RailItemListener,
-      listener: ImageLoadingListener
-    ) {
-      listener.onRequest()
-      image.setImageResource(glideRequests, media.uri, 0, 0, false, listener)
-      image.setOnClickListener { railItemListener.onRailItemClicked(media) }
-      captionIndicator.visibility = if (media.caption.isPresent) View.VISIBLE else View.GONE
-      setSelectedItem(isCurrentlySelected)
-    }
-
-    fun recycle() {
-      image.setOnClickListener(null)
-    }
-
-    fun setSelectedItem(isActive: Boolean) {
-      outline.visible = isActive
+    override fun bind(model: MediaRailItem) {
+      imageLoadingListener.onRequest()
+      image.setImageResource(glideRequests, model.media.uri, 0, 0, false, imageLoadingListener)
+      image.setOnClickListener { onRailItemSelected(model.media) }
+      captionIndicator.visibility = if (model.media.caption.isPresent) View.VISIBLE else View.GONE
 
-      val resId = if (isActive) R.drawable.mediapreview_rail_item_overlay_selected else R.drawable.mediapreview_rail_item_overlay_unselected
-      overlay.setImageResource(resId)
+      outline.visible = model.isSelected
+      overlay.setImageResource(if (model.isSelected) R.drawable.mediapreview_rail_item_overlay_selected else R.drawable.mediapreview_rail_item_overlay_unselected)
     }
   }
 
-  fun interface RailItemListener {
-    fun onRailItemClicked(media: Media)
-  }
-
   abstract class ImageLoadingListener : RequestListener<Drawable?> {
     private val activeJobs = AtomicInteger()
     fun onRequest() {
@@ -125,14 +116,4 @@ class MediaRailAdapter(private val glideRequests: GlideRequests, listener: RailI
 
     abstract fun onAllRequestsFinished()
   }
-
-  class MediaDiffer : DiffUtil.ItemCallback<Media>() {
-    override fun areItemsTheSame(oldItem: Media, newItem: Media): Boolean {
-      return oldItem.uri == newItem.uri
-    }
-
-    override fun areContentsTheSame(oldItem: Media, newItem: Media): Boolean {
-      return oldItem == newItem
-    }
-  }
 }