チャットのスクロール制御リファクタ

app/src/main/kotlin/com/cyder/android/syncpod/util/CustomBinder.kt

@@ -1,6 +1,8 @@
 package com.cyder.android.syncpod.util
 
 import android.databinding.BindingAdapter
+import android.databinding.InverseBindingAdapter
+import android.databinding.InverseBindingListener
 import android.support.v7.widget.LinearLayoutManager
 import android.support.v7.widget.RecyclerView
 import android.support.v7.widget.SwitchCompat
@@ -39,10 +41,11 @@ fun TextView.setLinksNavigable(flag: Boolean) {
 @BindingAdapter("onEnterClick")
 fun EditText.setKeyboardClick(listener: TextView.OnEditorActionListener) = setOnEditorActionListener(listener)
 
-@BindingAdapter(value = ["onScrolled", "onScrollStateChanged"], requireAll = false)
+@BindingAdapter(value = ["onScrolled", "onScrollStateChanged", "scrollAttrChanged"], requireAll = false)
 fun RecyclerView.setOnScrollChangedListeners(
         onScrolled: OnScrolledListener?,
-        onScrollStateChanged: OnScrollStateChangedListener?
+        onScrollStateChanged: OnScrollStateChangedListener?,
+        scrollAttrChanged: InverseBindingListener?
 ) {
     val OFFSET = 5
     val listener = object : RecyclerView.OnScrollListener() {
@@ -57,6 +60,7 @@ fun RecyclerView.setOnScrollChangedListeners(
             val nowHeadPos = layoutManager.findFirstVisibleItemPosition()
             val lastPos = layoutManager.findLastCompletelyVisibleItemPosition()
             onScrolled?.onScrolled(totalCount <= childCount + nowHeadPos + OFFSET)
+            scrollAttrChanged?.onChange()
         }
     }
 
@@ -71,6 +75,21 @@ interface OnScrollStateChangedListener {
     fun onScrollStateChanged(recycler: RecyclerView, newState: Int)
 }
 
+@BindingAdapter("scrollToEnd")
+fun RecyclerView.setScrollToEnd(flag: Boolean) {
+    if (flag && !isScrollToEnd()) {
+        smoothScrollToPosition(adapter.itemCount)
+    }
+}
+
+@InverseBindingAdapter(attribute = "scrollToEnd", event = "scrollAttrChanged")
+fun RecyclerView.isScrollToEnd(): Boolean {
+    val manager = layoutManager as LinearLayoutManager
+    val lastVisiblePosition = manager.findLastVisibleItemPosition()
+    val lastListPosition = adapter.itemCount - 1
+    return lastListPosition == lastVisiblePosition
+}
+
 @BindingAdapter(value = ["animatedVisibility", "originalHeight", "animationDuration"])
 fun View.setAnimatedVisibility(
         visibility: Int,

app/src/main/kotlin/com/cyder/android/syncpod/view/fragment/ChatFragment.kt

@@ -44,8 +44,6 @@ class ChatFragment : BaseFragment() {
         val manager = LinearLayoutManager(activity)
         manager.stackFromEnd = true
         val adapter = ChatAdapter(viewModel.chatViewModels)
-        val dataObserver = AutoScrollDataObserver(manager, adapter)
-        adapter.registerAdapterDataObserver(dataObserver)
         binding.chatList.adapter = adapter
         binding.chatList.layoutManager = manager
         binding.chatList.addItemDecoration(DividerItemDecoration(binding.chatList.context, manager.orientation))
@@ -61,20 +59,6 @@ class ChatFragment : BaseFragment() {
         }
     }
 
-    inner class AutoScrollDataObserver(
-            private val manager: LinearLayoutManager,
-            private val adapter: ChatAdapter
-    ) : RecyclerView.AdapterDataObserver() {
-        override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
-            super.onItemRangeInserted(positionStart, itemCount)
-            val lastVisiblePosition = manager.findLastVisibleItemPosition()
-            val lastListPosition = adapter.itemCount - 1
-            if (lastListPosition - 1 == lastVisiblePosition) {
-                binding.chatList.smoothScrollToPosition(lastListPosition + 1)
-            }
-        }
-    }
-
     companion object {
         fun createInstance() = ChatFragment()
     }

app/src/main/kotlin/com/cyder/android/syncpod/viewmodel/ChatFragmentViewModel.kt

@@ -1,6 +1,7 @@
 package com.cyder.android.syncpod.viewmodel
 
 import android.databinding.ObservableArrayList
+import android.databinding.ObservableBoolean
 import android.databinding.ObservableField
 import android.databinding.ObservableList
 import com.cyder.android.syncpod.model.Chat
@@ -22,6 +23,7 @@ class ChatFragmentViewModel @Inject constructor(
         private val repository: ChatRepository
 ) : FragmentViewModel() {
     var chatViewModels: ObservableList<ChatViewModel> = ObservableArrayList()
+    var scrolledToEnd = ObservableBoolean()
     private val onPauseSubject = PublishSubject.create<Unit>()
 
     override fun onStart() {
@@ -45,7 +47,7 @@ class ChatFragmentViewModel @Inject constructor(
                     ChatViewModel(ObservableField(it))
                 }
                 .subscribe {
-                    chatViewModels.add(it)
+                    addChat(it)
                 }
     }
 
@@ -60,6 +62,15 @@ class ChatFragmentViewModel @Inject constructor(
         return chats.map { ChatViewModel(ObservableField(it)) }
     }
 
+    private fun addChat(chatViewModel: ChatViewModel) {
+        val isScrolledToEnd = scrolledToEnd.get()
+        scrolledToEnd.set(false)
+        chatViewModels.add(chatViewModel)
+        if (isScrolledToEnd) {
+            scrolledToEnd.set(true)
+        }
+    }
+
     companion object {
         val INVOCATION = Unit
     }

app/src/main/res/layout/fragment_chat.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<layout xmlns:android="http://schemas.android.com/apk/res/android">
+<layout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto">
 
     <data>
 
@@ -15,6 +16,7 @@
         <android.support.v7.widget.RecyclerView
             android:id="@+id/chat_list"
             android:layout_width="match_parent"
-            android:layout_height="match_parent" />
+            android:layout_height="match_parent"
+            app:scrollToEnd="@={viewModel.scrolledToEnd}" />
     </LinearLayout>
 </layout>