Fix #2.

CHANGELOG.md

@@ -1,3 +1,7 @@
+## [1.0.2] - 2021-02-08
+
+* Fix #2 (https://github.com/deakjahn/huge_listview/issues/2).
+
 ## [1.0.1] - 2020-10-29
 
 * Different scroll thumbs.

lib/src/draggable_scrollbar.dart

@@ -11,6 +11,7 @@ class DraggableScrollbar extends StatefulWidget {
   final EdgeInsetsGeometry padding;
   final int totalCount;
   final int initialScrollIndex;
+  final int currentFirstIndex;
   final ValueChanged<double> onChange;
   final ScrollThumbBuilder scrollThumbBuilder;
 
@@ -23,6 +24,7 @@ class DraggableScrollbar extends StatefulWidget {
     this.padding,
     this.totalCount = 1,
     this.initialScrollIndex = 0,
+    this.currentFirstIndex = 0,
     @required this.scrollThumbBuilder,
     this.onChange,
   })  : assert(child != null),
@@ -79,7 +81,7 @@ class DraggableScrollbarState extends State<DraggableScrollbar> with TickerProvi
           alignment: Alignment.topRight,
           margin: EdgeInsets.only(top: thumbOffset),
           padding: widget.padding,
-          child: widget.scrollThumbBuilder?.call(widget.backgroundColor, widget.drawColor, widget.heightScrollThumb),
+          child: widget.scrollThumbBuilder?.call(widget.backgroundColor, widget.drawColor, widget.heightScrollThumb, widget.currentFirstIndex),
         ),
       );
 

lib/src/draggable_scrollbar_thumbs.dart

@@ -1,9 +1,9 @@
 import 'package:flutter/material.dart';
 
-typedef ScrollThumbBuilder = Widget Function(Color backgroundColor, Color drawColor, double height);
+typedef ScrollThumbBuilder = Widget Function(Color backgroundColor, Color drawColor, double height, int index);
 
 class DraggableScrollbarThumbs {
-  static Widget RoundedRectThumb(Color backgroundColor, Color drawColor, double height) {
+  static Widget RoundedRectThumb(Color backgroundColor, Color drawColor, double height, int index) {
     return Material(
       elevation: 4.0,
       child: Container(
@@ -14,7 +14,7 @@ class DraggableScrollbarThumbs {
     );
   }
 
-  static Widget ArrowThumb(Color backgroundColor, Color drawColor, double height) {
+  static Widget ArrowThumb(Color backgroundColor, Color drawColor, double height, int index) {
     return ClipPath(
       child: Container(
         width: 20.0,
@@ -28,7 +28,7 @@ class DraggableScrollbarThumbs {
     );
   }
 
-  static Widget SemicircleThumb(Color backgroundColor, Color drawColor, double height) {
+  static Widget SemicircleThumb(Color backgroundColor, Color drawColor, double height, int index) {
     return CustomPaint(
       foregroundPainter: _ArrowCustomPainter(drawColor),
       child: Material(

lib/src/huge_listview.dart

@@ -118,11 +118,20 @@ class HugeListViewState<T> extends State<HugeListView<T>> {
   }
 
   void _sendScroll() {
-    int current = listener.itemPositions.value.first.index;
+    int current = _currentFirst();
     widget.firstShown?.call(current);
     scrollKey.currentState?.setPosition(current / widget.totalCount);
   }
 
+  int _currentFirst() {
+    try {
+      return listener.itemPositions.value.first.index;
+    }
+    catch (e) {
+      return 0;
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     if (error != null && widget.errorBuilder != null) return widget.errorBuilder(context, error);
@@ -142,6 +151,7 @@ class HugeListViewState<T> extends State<HugeListView<T>> {
           backgroundColor: widget.thumbBackgroundColor,
           drawColor: widget.thumbDrawColor,
           heightScrollThumb: widget.thumbHeight,
+          currentFirstIndex: _currentFirst(),
           child: ScrollablePositionedList.builder(
             itemScrollController: widget.controller,
             itemPositionsListener: listener,

pubspec.lock

@@ -94,14 +94,14 @@ packages:
       name: quiver
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.4+1"
+    version: "2.1.5"
   scrollable_positioned_list:
     dependency: "direct main"
     description:
       name: scrollable_positioned_list
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.1.8"
+    version: "0.1.9"
   sky_engine:
     dependency: transitive
     description: flutter

pubspec.yaml

@@ -1,6 +1,6 @@
 name: huge_listview
 description: A performant list with any number of items.
-version: 1.0.1
+version: 1.0.2
 homepage: https://github.com/deakjahn/huge_listview
 
 environment: