Close #22402: Add top placeholder for home

app/src/androidTest/java/org/mozilla/fenix/perf/StartupExcessiveResourceUseTest.kt

@@ -25,7 +25,7 @@ private const val EXPECTED_SUPPRESSION_COUNT = 19
 @Suppress("TopLevelPropertyNaming") // it's silly this would have a different naming convention b/c no const
 private val EXPECTED_RUNBLOCKING_RANGE = 0..1 // CI has +1 counts compared to local runs: increment these together
 private const val EXPECTED_RECYCLER_VIEW_CONSTRAINT_LAYOUT_CHILDREN = 4
-private const val EXPECTED_NUMBER_OF_INFLATION = 12
+private const val EXPECTED_NUMBER_OF_INFLATION = 13
 
 private val failureMsgStrictMode = getErrorMessage(
     shortName = "StrictMode suppression",

app/src/main/java/org/mozilla/fenix/home/HomeFragment.kt

@@ -377,8 +377,7 @@ class HomeFragment : Fragment() {
             homeFragmentStore,
             binding.sessionControlRecyclerView,
             viewLifecycleOwner,
-            sessionControlInteractor,
-            homeViewModel
+            sessionControlInteractor
         )
 
         updateSessionControlView()
@@ -546,8 +545,6 @@ class HomeFragment : Fragment() {
         if (bundleArgs.getBoolean(FOCUS_ON_ADDRESS_BAR)) {
             navigateToSearch()
         } else if (bundleArgs.getLong(FOCUS_ON_COLLECTION, -1) >= 0) {
-            // No need to scroll to async'd loaded TopSites if we want to scroll to collections.
-            homeViewModel.shouldScrollToTopSites = false
             /* Triggered when the user has added a tab to a collection and has tapped
             * the View action on the [TabsTrayDialogFragment] snackbar.*/
             scrollAndAnimateCollection(bundleArgs.getLong(FOCUS_ON_COLLECTION, -1))

app/src/main/java/org/mozilla/fenix/home/HomeScreenViewModel.kt

@@ -11,9 +11,4 @@ class HomeScreenViewModel : ViewModel() {
      * Used to delete a specific session once the home screen is resumed
      */
     var sessionToDelete: String? = null
-
-    /**
-     * Used to remember if we need to scroll to top of the homeFragment's recycleView (top sites) see #8561
-     * */
-    var shouldScrollToTopSites: Boolean = true
 }

app/src/main/java/org/mozilla/fenix/home/TopPlaceholderViewHolder.kt

@@ -0,0 +1,24 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.fenix.home
+
+import android.view.View
+import org.mozilla.fenix.R
+import org.mozilla.fenix.utils.view.ViewHolder
+
+/**
+ * View holder for a synchronous, unconditional and invisible placeholder.  This is to anchor home to
+ * the top when home is created.
+ */
+class TopPlaceholderViewHolder(
+    view: View
+) : ViewHolder(view) {
+
+    fun bind() = Unit
+
+    companion object {
+        const val LAYOUT_ID = R.layout.top_placeholder_item
+    }
+}

app/src/main/java/org/mozilla/fenix/home/sessioncontrol/SessionControlAdapter.kt

@@ -23,6 +23,7 @@ import org.mozilla.fenix.components.tips.Tip
 import org.mozilla.fenix.historymetadata.view.HistoryMetadataGroupViewHolder
 import org.mozilla.fenix.historymetadata.view.HistoryMetadataHeaderViewHolder
 import org.mozilla.fenix.home.HomeFragmentStore
+import org.mozilla.fenix.home.TopPlaceholderViewHolder
 import org.mozilla.fenix.home.OnboardingState
 import org.mozilla.fenix.home.recentbookmarks.view.RecentBookmarksViewHolder
 import org.mozilla.fenix.home.recenttabs.view.RecentTabViewHolder
@@ -49,6 +50,7 @@ import org.mozilla.fenix.home.topsites.TopSitePagerViewHolder
 import mozilla.components.feature.tab.collections.Tab as ComponentTab
 
 sealed class AdapterItem(@LayoutRes val viewType: Int) {
+    object TopPlaceholderItem : AdapterItem(TopPlaceholderViewHolder.LAYOUT_ID)
     data class TipItem(val tip: Tip) : AdapterItem(
         ButtonTipViewHolder.LAYOUT_ID
     )
@@ -255,6 +257,7 @@ class SessionControlAdapter(
 
         val view = LayoutInflater.from(parent.context).inflate(viewType, parent, false)
         return when (viewType) {
+            TopPlaceholderViewHolder.LAYOUT_ID -> TopPlaceholderViewHolder(view)
             ButtonTipViewHolder.LAYOUT_ID -> ButtonTipViewHolder(view, interactor)
             TopSitePagerViewHolder.LAYOUT_ID -> TopSitePagerViewHolder(view, interactor)
             PrivateBrowsingDescriptionViewHolder.LAYOUT_ID -> PrivateBrowsingDescriptionViewHolder(
@@ -350,6 +353,9 @@ class SessionControlAdapter(
                 val tipItem = item as AdapterItem.TipItem
                 holder.bind(tipItem.tip)
             }
+            is TopPlaceholderViewHolder -> {
+                holder.bind()
+            }
             is TopSitePagerViewHolder -> {
                 holder.bind((item as AdapterItem.TopSitePager).topSites)
             }

app/src/main/java/org/mozilla/fenix/home/sessioncontrol/SessionControlView.kt

@@ -20,7 +20,6 @@ import org.mozilla.fenix.ext.settings
 import org.mozilla.fenix.historymetadata.HistoryMetadataGroup
 import org.mozilla.fenix.home.HomeFragmentState
 import org.mozilla.fenix.home.HomeFragmentStore
-import org.mozilla.fenix.home.HomeScreenViewModel
 import org.mozilla.fenix.home.Mode
 import org.mozilla.fenix.home.OnboardingState
 import org.mozilla.fenix.home.recenttabs.RecentTab
@@ -46,6 +45,9 @@ internal fun normalModeAdapterItems(
     val items = mutableListOf<AdapterItem>()
     var shouldShowCustomizeHome = false
 
+    // Add a synchronous, unconditional and invisible placeholder so home is anchored to the top when created.
+    items.add(AdapterItem.TopPlaceholderItem)
+
     tip?.let { items.add(AdapterItem.TipItem(it)) }
 
     if (showSetAsDefaultBrowserCard) {
@@ -182,8 +184,7 @@ class SessionControlView(
     store: HomeFragmentStore,
     val containerView: View,
     viewLifecycleOwner: LifecycleOwner,
-    internal val interactor: SessionControlInteractor,
-    private var homeScreenViewModel: HomeScreenViewModel
+    internal val interactor: SessionControlInteractor
 ) {
 
     val view: RecyclerView = containerView as RecyclerView
@@ -222,20 +223,6 @@ class SessionControlView(
 
         if (shouldReportMetrics) interactor.reportSessionMetrics(state)
 
-        val stateAdapterList = state.toAdapterList()
-        if (homeScreenViewModel.shouldScrollToTopSites) {
-            sessionControlAdapter.submitList(stateAdapterList) {
-
-                val loadedTopSites = stateAdapterList.find { adapterItem ->
-                    adapterItem is AdapterItem.TopSitePager && adapterItem.topSites.isNotEmpty()
-                }
-                loadedTopSites?.run {
-                    homeScreenViewModel.shouldScrollToTopSites = false
-                    view.scrollToPosition(0)
-                }
-            }
-        } else {
-            sessionControlAdapter.submitList(stateAdapterList)
-        }
+        sessionControlAdapter.submitList(state.toAdapterList())
     }
 }

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

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+<View xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="0dp"/>

app/src/test/java/org/mozilla/fenix/home/sessioncontrol/SessionControlViewTest.kt

@@ -14,6 +14,7 @@ import mozilla.components.feature.tab.collections.TabCollection
 import mozilla.components.feature.top.sites.TopSite
 import mozilla.components.service.pocket.PocketRecommendedStory
 import mozilla.components.support.test.robolectric.testContext
+import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Assert.assertFalse
 import org.junit.Test
@@ -96,8 +97,7 @@ class SessionControlViewTest {
             mockk(relaxed = true),
             view,
             mockk(relaxed = true),
-            interactor,
-            mockk(relaxed = true)
+            interactor
         )
         val recentTabs = listOf<RecentTab>(mockk(relaxed = true))
 
@@ -118,8 +118,7 @@ class SessionControlViewTest {
             mockk(relaxed = true),
             view,
             mockk(relaxed = true),
-            interactor,
-            mockk(relaxed = true)
+            interactor
         )
 
         val state = HomeFragmentState()
@@ -155,8 +154,9 @@ class SessionControlViewTest {
             pocketArticles
         )
 
-        assertTrue(results[0] is AdapterItem.RecentBookmarks)
-        assertTrue(results[1] is AdapterItem.CustomizeHomeButton)
+        assertTrue(results[0] is AdapterItem.TopPlaceholderItem)
+        assertTrue(results[1] is AdapterItem.RecentBookmarks)
+        assertTrue(results[2] is AdapterItem.CustomizeHomeButton)
     }
 
     @Test
@@ -182,9 +182,10 @@ class SessionControlViewTest {
             pocketArticles
         )
 
-        assertTrue(results[0] is AdapterItem.RecentTabsHeader)
-        assertTrue(results[1] is AdapterItem.RecentTabItem)
-        assertTrue(results[2] is AdapterItem.CustomizeHomeButton)
+        assertTrue(results[0] is AdapterItem.TopPlaceholderItem)
+        assertTrue(results[1] is AdapterItem.RecentTabsHeader)
+        assertTrue(results[2] is AdapterItem.RecentTabItem)
+        assertTrue(results[3] is AdapterItem.CustomizeHomeButton)
     }
 
     @Test
@@ -210,9 +211,10 @@ class SessionControlViewTest {
             pocketArticles
         )
 
-        assertTrue(results[0] is AdapterItem.HistoryMetadataHeader)
-        assertTrue(results[1] is AdapterItem.HistoryMetadataGroup)
-        assertTrue(results[2] is AdapterItem.CustomizeHomeButton)
+        assertTrue(results[0] is AdapterItem.TopPlaceholderItem)
+        assertTrue(results[1] is AdapterItem.HistoryMetadataHeader)
+        assertTrue(results[2] is AdapterItem.HistoryMetadataGroup)
+        assertTrue(results[3] is AdapterItem.CustomizeHomeButton)
     }
 
     @Test
@@ -238,8 +240,9 @@ class SessionControlViewTest {
             pocketArticles
         )
 
-        assertTrue(results[0] is AdapterItem.PocketStoriesItem)
-        assertTrue(results[1] is AdapterItem.CustomizeHomeButton)
+        assertTrue(results[0] is AdapterItem.TopPlaceholderItem)
+        assertTrue(results[1] is AdapterItem.PocketStoriesItem)
+        assertTrue(results[2] is AdapterItem.CustomizeHomeButton)
     }
 
     @Test
@@ -264,6 +267,36 @@ class SessionControlViewTest {
             historyMetadata,
             pocketArticles
         )
-        assertTrue(results.isEmpty())
+        assertEquals(results.size, 1)
+        assertTrue(results[0] is AdapterItem.TopPlaceholderItem)
+    }
+
+    @Test
+    fun `GIVEN all items THEN top placeholder item is always the first item`() {
+        val collection = mockk<TabCollection> {
+            every { id } returns 123L
+        }
+        val topSites = listOf<TopSite>(mockk())
+        val collections = listOf(collection)
+        val expandedCollections = emptySet<Long>()
+        val recentBookmarks = listOf<BookmarkNode>(mockk())
+        val recentTabs = listOf<RecentTab.Tab>(mockk())
+        val historyMetadata = listOf<HistoryMetadataGroup>(mockk())
+        val pocketArticles = listOf<PocketRecommendedStory>(mockk())
+
+        val results = normalModeAdapterItems(
+            topSites,
+            collections,
+            expandedCollections,
+            null,
+            recentBookmarks,
+            false,
+            false,
+            recentTabs,
+            historyMetadata,
+            pocketArticles
+        )
+
+        assertTrue(results[0] is AdapterItem.TopPlaceholderItem)
     }
 }