Minor perf improvements (#1112)

lib/ui/home/memories/full_screen_memory.dart

@@ -1,3 +1,4 @@
+import "dart:async";
 import "dart:io";
 
 import "package:flutter/cupertino.dart";
@@ -56,6 +57,7 @@ class _FullScreenMemoryState extends State<FullScreenMemory> {
 
   @override
   Widget build(BuildContext context) {
+    _pageController ??= PageController(initialPage: _index);
     final file = widget.memories[_index].file;
     return Scaffold(
       appBar: AppBar(
@@ -140,6 +142,12 @@ class _FullScreenMemoryState extends State<FullScreenMemory> {
     );
   }
 
+  @override
+  void dispose() {
+    _pageController?.dispose();
+    super.dispose();
+  }
+
   Future<void> onFileDeleted(Memory removedMemory) async {
     if (!mounted) {
       return;
@@ -268,7 +276,6 @@ class _FullScreenMemoryState extends State<FullScreenMemory> {
   }
 
   Widget _buildSwiper() {
-    _pageController = PageController(initialPage: _index);
     return ExtentsPageView.extents(
       itemBuilder: (BuildContext context, int index) {
         if (index < widget.memories.length - 1) {
@@ -294,7 +301,9 @@ class _FullScreenMemoryState extends State<FullScreenMemory> {
       itemCount: widget.memories.length,
       controller: _pageController,
       onPageChanged: (index) async {
-        await MemoriesService.instance.markMemoryAsSeen(widget.memories[index]);
+        unawaited(
+          MemoriesService.instance.markMemoryAsSeen(widget.memories[index]),
+        );
         if (mounted) {
           setState(() {
             _index = index;

lib/ui/viewer/file/detail_page.dart

@@ -77,16 +77,17 @@ class _DetailPageState extends State<DetailPage> {
 
   @override
   void initState() {
+    super.initState();
     _files = [
       ...widget.config.files
     ]; // Make a copy since we append preceding and succeeding entries to this
     _selectedIndex = widget.config.selectedIndex;
     _preloadEntries();
-    super.initState();
   }
 
   @override
   void dispose() {
+    _pageController?.dispose();
     SystemChrome.setEnabledSystemUIMode(
       SystemUiMode.manual,
       overlays: SystemUiOverlay.values,
@@ -140,6 +141,8 @@ class _DetailPageState extends State<DetailPage> {
 
   Widget _buildPageView() {
     _logger.info("Building with " + _selectedIndex.toString());
+    // todo: perf.. fix this
+    _pageController?.dispose();
     _pageController = PageController(initialPage: _selectedIndex);
     return PageView.builder(
       itemBuilder: (context, index) {