Flutter开发 Swiper报错【_positions.is

使用Swiper控件的时候，更换Swiper数据源，需要加入 key: ValueKey(listWidget.length),

避免在Swiper控件出现的问题。

flutter: ══╡ EXCEPTION CAUGHT BY FOUNDATION LIBRARY ╞════════════════════════════════════════════════════════

flutter: The following assertion was thrown while dispatching notifications for SwiperController:

flutter: ScrollController not attached to any scroll views.

flutter: 'package:flutter/src/widgets/scroll_controller.dart':

package:flutter/…/widgets/scroll_controller.dart:1

flutter: Failed assertion: line 107 pos 12: '_positions.isNotEmpty'

flutter:

flutter: Either the assertion indicates an error in the framework itself, or we should provide substantially

flutter: more information in this error message to help you determine and fix the underlying cause.

flutter: In either case, please report this assertion by filing a bug on GitHub:

flutter:  https://github.com/flutter/flutter/issues/new?template=2_bug.md

以上方法可以解决，出现_positions.isNotEmpty的问题。顺便解释下解决方法的原理

static bool canUpdate(Widget oldWidget, Widget newWidget) {

return oldWidget.runtimeType == newWidget.runtimeType

&& oldWidget.key == newWidget.key;

}

本身是一个抽象类，有一个工厂程构造方法 ValueKey()。

直接子类主要有：LocalKey 跟 GlobalKey。

LocalKey 是增量算法的核心，决定哪个Element要保留，哪个Element要删除。以下是LocalKey的三个子类。

ValueKey：以值作为参数（数字、字符串）；

ObjectKey：以对象作为参数；

UniqueKey：创建唯一标识；

对应某一个  或者 State 或者 。

参考文献：https://baijiahao.baidu.com/s?id=1718959148055142446&wfr=spider&for=pc