setstate

问题 I have a root class RootPage which is a StatefulWidget which is always in view. I would like to change the body in RootPage which is controlled by RootPage\'s currentPage Widget from different classes such as my FeedPage class and any other class that I make? Example code import \'package:flutter/material.dart\'; class RootPage extends StatefulWidget { @override _RootPageState createState() => new _RootPageState(); } class _RootPageState extends State<RootPage> { FeedPage feedPage; Widget

问题 I\'m working on a todo application. This is a very simplified version of the offending code. I have a checkbox: <p><input type=\"checkbox\" name=\"area\" checked={this.state.Pencil} onChange={this.checkPencil}/> Writing Item </p> Here\'s the function that calls the checkbox: checkPencil(){ this.setState({ pencil:!this.state.pencil, }); this.props.updateItem(this.state); } updateItem is a function that\'s mapped to dispatch to redux function mapDispatchToProps(dispatch){ return

问题 I know that React may perform state updates asynchronously and in batch for performance optimization. Therefore you can never trust the state to be updated after having called setState . But can you trust React to update the state in the same order as setState is called for the same component? different components? Consider clicking the button in the following examples: 1. Is there ever a possibility that a is false and b is true for: class Container extends React.Component { constructor

问题 I\'m trying to organize my state by using nested property like this: this.state = { someProperty: { flag:true } } But updating state like this, this.setState({ someProperty.flag: false }); doesn\'t work. How can this be done correctly? 回答1: In order to setState for a nested object you can follow the below approach as I think setState doesn't handle nested updates. var someProperty = {...this.state.someProperty} someProperty.flag = true; this.setState({someProperty}) The idea is to create a