From 21d3a262628b9a0373cb9831106d92437c3deae9 Mon Sep 17 00:00:00 2001
From: Yinsee <yinsee@3b.my>
Date: Fri, 2 Oct 2020 18:45:00 +0800
Subject: [PATCH] Update page_turn.dart

- fix exception when going Prev() at the first page
- optimize rendering by hiding invisible pages using Offstage
---
 lib/page_turn.dart | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/page_turn.dart b/lib/page_turn.dart
index 077987f..c54a686 100644
--- a/lib/page_turn.dart
+++ b/lib/page_turn.dart
@@ -113,7 +113,7 @@ class PageTurnState extends State<PageTurn> with TickerProviderStateMixin {
         } else {
           await _controllers[pageNumber].forward();
         }
-      } else {
+      } else if (pageNumber > 0) {
         print(
             'Val:${_controllers[pageNumber - 1].value} -> ${widget.cutoff + 0.28}');
         if (!_isFirstPage &&
@@ -170,6 +170,7 @@ class PageTurnState extends State<PageTurn> with TickerProviderStateMixin {
 
   @override
   Widget build(BuildContext context) {
+    int i = 0;
     return Material(
       child: LayoutBuilder(
         builder: (context, dimens) => GestureDetector(
@@ -184,7 +185,13 @@ class PageTurnState extends State<PageTurn> with TickerProviderStateMixin {
                 widget.lastPage,
               ],
               if (pages != null)
-                ...pages
+                ...pages.map((p) {
+                  i++;
+                  final pn = pages.length - pageNumber;
+                  final ret = Offstage(
+                      offstage: !(i >= pn - 1 && i <= pn + 1), child: p);
+                  return ret;
+                }).toList()
               else ...[
                 Container(child: CircularProgressIndicator()),
               ],