只有当Widget发生结构变化,导致可滚动组件的State销毁或重新构建时才会丢失状态,这种情况就需要显式指定PageStorageKey,通过PageStorage来存储滚动位置,一个典型的场景是在使用TabBarView时,在Tab发生切换时,Tab页中的可滚动组件的State就会销毁,这时如果想恢复滚动位置就需要指定PageStorageKey。 ScrollPosition 真正保存滑动位...
import'package:flutter/material.dart';voidmain(){runApp(newMaterialApp(title:'Flutter Tutorial',home:newTutorialHome(),));}// 这里创建的为一个无状态的widgetclassTutorialHomeextendsStatelessWidget{@overrideWidgetbuild(BuildContextcontext){//Scaffold是Material中主要的布局组件.returnnewScaffold(appBar:newAp...
// inside a setState call to trigger a rebuild. The framework then calls // build, below, which updates the visual appearance of the app. if (inCart) _shoppingCart.add(product); else _shoppingCart.remove(product); }); } @override Widget build(BuildContext context) { return new Scaffold...
❝实例代码可见:https://github.com/CarGuo/gsy_flutter_demo/blob/master/lib/widget/chat_list_scroll_demo_page_2.dart
('While the widget tree was being built, laid out, and painted, ''a new frame was scheduled to rebuild the widget tree.',),ErrorHint('This might be because setState() was called from a layout or ''paint callback. ''If a change is needed to the widget tree, it should be applied...
Widget第一次被加载(Widget 第一次被加入到 Widget Tree 中 ,更准确地说是其对应的 Element 被加入到 Element Tree 时,即 Element 被挂载(mount)时) Parent Widget 修改了其配置信息; 该Widget 依赖的Inherited Widget发生变化时。 当Parent Widget或 依赖的Inherited Widget频繁变化时,build方法也会频繁被调用。
The url i open has a content that reproduce some sounds, but when Widget is closed (onNavigationRequest if clause is satisfied or user press back button on Android), i can still hear sounds from webview, like the StatefulWidget is not disposed correctly....
1.由于您希望为maxLines添加条件 maxLines: MediaQuery.of(context).size.width < 389 ? 6 : 5 1....
一个widget的构建函数应该是没有副作用的。每当函数被要求构建时,widget应该返回一个新的widgets树1,不管widget之前返回的是什么。框架会做繁重的工作,根据渲染对象树来决定哪些构建方法需要被调用(后面会详细介绍)。关于这个过程的更多信息可以在Inside Flutter主题中找到。
But what if I need to get the size during the build! What can I do? There's one cool widget that can help: Overlay and its OverlayEntry. They are used to display widgets on top of everything else (similar to the stack). But the coolest thing is that they are on a different buil...