Fix scroll to bottom button visibility logic

app/src/main/java/org/thoughtcrime/securesms/conversation/v2/ConversationActivityV2.kt

@@ -9,6 +9,7 @@ import android.graphics.Rect
 import android.graphics.Typeface
 import android.os.AsyncTask
 import android.os.Bundle
+import android.util.Log
 import android.util.TypedValue
 import android.view.*
 import android.widget.RelativeLayout
@@ -17,6 +18,7 @@ import androidx.lifecycle.ViewModelProviders
 import androidx.loader.app.LoaderManager
 import androidx.loader.content.Loader
 import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
 import kotlinx.android.synthetic.main.activity_conversation_v2.*
 import kotlinx.android.synthetic.main.activity_conversation_v2.view.*
 import kotlinx.android.synthetic.main.activity_conversation_v2_action_bar.*
@@ -62,9 +64,7 @@ import kotlin.math.*
 // price we pay is a bit of back and forth between the input bar and the conversation activity.
 
 class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDelegate,
-    InputBarRecordingViewDelegate, ConversationRecyclerViewDelegate {
+    InputBarRecordingViewDelegate {
-    private val scrollButtonFullVisibilityThreshold by lazy { toPx(120.0f, resources) }
-    private val scrollButtonNoVisibilityThreshold by lazy { toPx(20.0f, resources) }
     private val screenWidth = Resources.getSystem().displayMetrics.widthPixels
     private var linkPreviewViewModel: LinkPreviewViewModel? = null
     private var threadID: Long = -1
@@ -142,7 +142,6 @@ class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDe
         conversationRecyclerView.adapter = adapter
         val layoutManager = LinearLayoutManager(this, LinearLayoutManager.VERTICAL, true)
         conversationRecyclerView.layoutManager = layoutManager
-        conversationRecyclerView.delegate = this
         // Workaround for the fact that CursorRecyclerViewAdapter doesn't auto-update automatically (even though it says it will)
         LoaderManager.getInstance(this).restartLoader(0, null, object : LoaderManager.LoaderCallbacks<Cursor> {
 
@@ -158,6 +157,12 @@ class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDe
                 adapter.changeCursor(null)
             }
         })
+        conversationRecyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
+
+            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
+                handleRecyclerViewScrolled()
+            }
+        })
     }
 
     private fun setUpToolBar() {
@@ -417,12 +422,11 @@ class ConversationActivityV2 : PassphraseRequiredActionBarActivity(), InputBarDe
         animation.start()
     }
 
-    override fun handleConversationRecyclerViewBottomOffsetChanged(bottomOffset: Int) {
+    private fun handleRecyclerViewScrolled() {
-        val rawAlpha = (bottomOffset.toFloat() - scrollButtonNoVisibilityThreshold) /
+        val position = layoutManager.findFirstCompletelyVisibleItemPosition()
-            (scrollButtonFullVisibilityThreshold - scrollButtonNoVisibilityThreshold)
+        val alpha = if (position > 0) 1.0f else 0.0f
-        val alpha = max(min(rawAlpha, 1.0f), 0.0f)
         scrollToBottomButton.alpha = alpha
-        unreadCount = layoutManager.findFirstVisibleItemPosition()
+        unreadCount = min(unreadCount, layoutManager.findFirstVisibleItemPosition())
         updateUnreadCountIndicator()
     }
 

app/src/main/java/org/thoughtcrime/securesms/conversation/v2/ConversationRecyclerView.kt

@@ -17,7 +17,6 @@ class ConversationRecyclerView : RecyclerView {
     private val maxLongPressVelocityY = toPx(10, resources)
     private val minSwipeVelocityX = toPx(10, resources)
     private var velocityTracker: VelocityTracker? = null
-    var delegate: ConversationRecyclerViewDelegate? = null
 
     constructor(context: Context) : super(context) { initialize() }
     constructor(context: Context, attrs: AttributeSet) : super(context, attrs) { initialize() }
@@ -25,18 +24,6 @@ class ConversationRecyclerView : RecyclerView {
 
     private fun initialize() {
         disableClipping()
-        addOnScrollListener(object : RecyclerView.OnScrollListener() {
-            private var bottomOffset = 0
-
-            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
-                // Do nothing
-            }
-
-            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
-                bottomOffset += dy // FIXME: Not sure this is fully accurate, but it seems close enough
-                delegate?.handleConversationRecyclerViewBottomOffsetChanged(abs(bottomOffset))
-            }
-        })
     }
 
     override fun onInterceptTouchEvent(e: MotionEvent): Boolean {
@@ -66,8 +53,3 @@ class ConversationRecyclerView : RecyclerView {
         return super.dispatchTouchEvent(e)
     }
 }
-
-interface ConversationRecyclerViewDelegate {
-
-    fun handleConversationRecyclerViewBottomOffsetChanged(bottomOffset: Int)
-}