reactjs —解决setState异步问题

Question

I've read this post: React setState not Updating Immediately

and realized that setState is async and may require a second arg as a function to deal with the new state.

Now I have a checkbox

class CheckBox extends Component {
    constructor() {
        super();
        this.state = {
            isChecked: false,
            checkedList: []
        };
        this.handleChecked = this.handleChecked.bind(this);
    }

    handleChecked () {
        this.setState({isChecked: !this.state.isChecked}, this.props.handler(this.props.txt));
    }

    render () {
        return (
            <div>
                <input type="checkbox" onChange={this.handleChecked} />
                {`   ${this.props.txt}`}
            </div>
            )
    }
}

And is being used by another app

class AppList extends Component {
    constructor() {
        super();
        this.state = {
            checked: [],
            apps: []
        };
        this.handleChecked = this.handleChecked.bind(this);
        this.handleDeleteKey = this.handleDeleteKey.bind(this);
    }
    handleChecked(client_id) {
        if (!this.state.checked.includes(client_id)) {
            let new_apps = this.state.apps;
            if (new_apps.includes(client_id)) {
                new_apps = new_apps.filter(m => {
                    return (m !== client_id);
                });
            } else {
                new_apps.push(client_id);
            }
            console.log('new apps', new_apps);
            this.setState({apps: new_apps});
            // this.setState({checked: [...checked_key, client_id]});
            console.log(this.state);
        }
    }
    render () {
        const apps = this.props.apps.map((app) =>
            <CheckBox key={app.client_id} txt={app.client_id} handler={this.handleChecked}/>
        );

        return (
            <div>
                <h4>Client Key List:</h4>
                {this.props.apps.length > 0 ? <ul>{apps}</ul> : <p>No Key</p>}
            </div> 
        );
    }


}

So every time the checkbox status changes, I update the this.state.apps in AppList

when I console.log new_apps , everything works accordingly, but console.log(this.state) shows that the state is not updated immediately, which is expected. What I need to know is how I can ensure the state is updated when I need to do further actions (like register all these selected strings or something)

Answer 1

setState enables you to make a callback function after you set the state so you can get the real state

this.setState({stateYouWant}, () => console.log(this.state.stateYouWant))

in your case:

this.setState({apps: new_apps}, () => console.log(this.state))

Answer 2

The others have the right answer regarding the setState callback, but I would also suggest making CheckBox stateless and pass isChecked from MyApp as a prop. This way you're only keeping one record of whether the item is checked, and don't need to synchronise between the two.

Answer 3

Actually there shouldn't be two states keeping the same thing. Instead, the checkbox should be stateless, the state should only be kept at the AppList and then passed down:

 const CheckBox = ({ text, checked, onChange }) => (<span><input type="checkbox" checked={checked} onChange={() => onChange(text)} />{text}</span>); class AppList extends React.Component { constructor() { super(); this.state = { apps: [ {name: "One", checked: false }, { name: "Two", checked: false } ], }; } onChange(app) { this.setState( previous => ({ apps: previous.apps.map(({ name, checked }) => ({ name, checked: checked !== (name === app) })), }), () => console.log(this.state) ); } render() { return <div> {this.state.apps.map(({ name, checked }) => (<CheckBox text={name} checked={checked} onChange={this.onChange.bind(this)} />))} </div>; } } ReactDOM.render(<AppList />, document.body); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>