For #11660: added prefetch for topsites and update in onCreateView()

app/src/main/java/org/mozilla/fenix/FenixApplication.kt

@@ -142,6 +142,7 @@ open class FenixApplication : LocaleAwareApplication() {
             }
         }
 
+        prefetchForHomeFragment()
         setupLeakCanary()
         if (settings().isTelemetryEnabled) {
             components.analytics.metrics.start(MetricServiceType.Data)
@@ -228,6 +229,13 @@ open class FenixApplication : LocaleAwareApplication() {
         // no-op, LeakCanary is disabled by default
     }
 
+    // This is for issue https://github.com/mozilla-mobile/fenix/issues/11660. We prefetch our info for startup
+    // so that we're sure that we have all the data available as our fragment is launched.
+    private fun prefetchForHomeFragment() {
+        StrictMode.allowThreadDiskReads().resetPoliciesAfter {
+            components.core.topSiteStorage.prefetch()
+        }
+    }
     private fun setupPush() {
         // Sets the PushFeature as the singleton instance for push messages to go to.
         // We need the push feature setup here to deliver messages in the case where the service

app/src/main/java/org/mozilla/fenix/components/TopSiteStorage.kt

@@ -14,6 +14,7 @@ import mozilla.components.feature.top.sites.TopSite
 import mozilla.components.feature.top.sites.TopSiteStorage
 import mozilla.components.support.locale.LocaleManager
 import org.mozilla.fenix.R
+import org.mozilla.fenix.ext.observeOnce
 import org.mozilla.fenix.ext.settings
 import org.mozilla.fenix.settings.SupportUtils
 import org.mozilla.fenix.settings.advanced.getSelectedLocale
@@ -86,4 +87,10 @@ class TopSiteStorage(private val context: Context) {
             context.settings().defaultTopSitesAdded = true
         }
     }
+
+    fun prefetch() {
+        getTopSites().observeOnce {
+            cachedTopSites = it
+        }
+    }
 }

app/src/main/java/org/mozilla/fenix/ext/LiveData.kt

@@ -0,0 +1,20 @@
+/* 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.ext
+
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.Observer
+
+/**
+ * Observe a LiveData once and unregister from it as soon as the live data returns a value
+ */
+fun <T> LiveData<T>.observeOnce(observer: (T) -> Unit) {
+    observeForever(object : Observer<T> {
+        override fun onChanged(value: T) {
+            removeObserver(this)
+            observer(value)
+        }
+    })
+}

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

@@ -215,11 +215,10 @@ class HomeFragment : Fragment() {
             sessionControlInteractor,
             homeViewModel
         )
-        activity.themeManager.applyStatusBarTheme(activity)
 
-        view.consumeFrom(homeFragmentStore, viewLifecycleOwner) {
-            sessionControlView?.update(it)
-        }
+        updateSessionControlView(view)
+
+        activity.themeManager.applyStatusBarTheme(activity)
 
         view.consumeFrom(requireComponents.core.store, viewLifecycleOwner) {
             val tabCount = if (currentMode.getCurrentMode() == Mode.Normal) {
@@ -234,6 +233,20 @@ class HomeFragment : Fragment() {
         return view
     }
 
+    /**
+     * The [SessionControlView] is forced to update with our current state when we call
+     * [HomeFragment.onCreateView] in order to be able to draw everything at once with the current
+     * data in our store. The [View.consumeFrom] coroutine dispatch
+     * doesn't get run right away which means that we won't draw on the first layout pass.
+     */
+    fun updateSessionControlView(view: View) {
+        sessionControlView?.update(homeFragmentStore.state)
+
+        view.consumeFrom(homeFragmentStore, viewLifecycleOwner) {
+            sessionControlView?.update(it)
+        }
+    }
+
     private fun updateLayout(view: View) {
         val shouldUseBottomToolbar = view.context.settings().shouldUseBottomToolbar
 

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

@@ -4,7 +4,6 @@
 
 package org.mozilla.fenix.home.sessioncontrol
 
-import android.os.Build
 import android.view.View
 import androidx.recyclerview.widget.ItemTouchHelper
 import androidx.recyclerview.widget.LinearLayoutManager
@@ -142,13 +141,8 @@ class SessionControlView(
     }
 
     fun update(state: HomeFragmentState) {
-        // Workaround for list not updating until scroll on Android 5 + 6
-        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N) {
-            sessionControlAdapter.submitList(null)
-        }
 
         val stateAdapterList = state.toAdapterList()
-
         if (homeScreenViewModel.shouldScrollToTopSites) {
             sessionControlAdapter.submitList(stateAdapterList) {