[英]How to keep the scrolling position when adding a new elements in the top using ListView or CustomScrollView in Flutter
是否可以将新元素添加到 ListVeiw 或 CustomScrollView 的顶部并保持滚动 position 与 Flutter 一样
我试过以下
extentAfter = _scrollController.position.extentAfter;
_scrollController.jumpTo(_scrollController.position.maxScrollExtent - extentAfter);
但这不适用于 SliverAppBar - 浮动且实际上不是最佳解决方案。
实际上,最干净的方法是仅在用户滚动回 ListView 顶部时才添加这些项目。 您可以将它们缓存在 memory 中,因为用户距离列表顶部(在您的情况下)足够远。
添加physics: const AllwaysScrollableFixedPositionScrollPhysics(),
到您的CustomScrollView
如果用户在列表的边缘,新项目会自动滚动到
import 'package:flutter/material.dart';
class AllwaysScrollableFixedPositionScrollPhysics extends ScrollPhysics {
/// Creates scroll physics that always lets the user scroll.
const AllwaysScrollableFixedPositionScrollPhysics({ScrollPhysics? parent})
: super(parent: parent);
@override
AllwaysScrollableFixedPositionScrollPhysics applyTo(ScrollPhysics? ancestor) {
return AllwaysScrollableFixedPositionScrollPhysics(parent: buildParent(ancestor));
}
@override
double adjustPositionForNewDimensions({
required ScrollMetrics oldPosition,
required ScrollMetrics newPosition,
required bool isScrolling,
required double velocity,
}) {
if (newPosition.extentBefore == 0) {
return super.adjustPositionForNewDimensions(
oldPosition: oldPosition,
newPosition: newPosition,
isScrolling: isScrolling,
velocity: velocity,
);
}
return newPosition.maxScrollExtent - oldPosition.extentAfter;
}
@override
bool shouldAcceptUserOffset(ScrollMetrics position) => true;
}
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