React JS 组件在 Meteor 中多次渲染

Question

I using Meteor 1.3 for this application together with react js and Tracker React. I have a page to view all available users in the application. This page require user to login to view the data. If user not logged in, it will shows the login form and once logged-in the component will render the user's data.

Main component for the logic.

export default class MainLayout extends TrackerReact(React.Component) {
    
    isLogin() {
        return Meteor.userId() ? true : false
    }
    render() {
    
        if(!this.isLogin()){
            return (<Login />)
        }else{
        return (
            <div className="container">
                <AllUserdata  />            
            </div>
          )
        }
    }
}

And in the AllUserdata component:

export default class Users extends TrackerReact(React.Component) {

    constructor() {
        super();

        this.state ={
            subscription: {
                Allusers : Meteor.subscribe("AllUsers")
            }
        }

    }

    componentWillUnmount(){
        this.state.subscription.Allusers.stop();
    }

    allusers() {
        return Meteor.users.find().fetch();
    }

    render() {
        console.log('User objects ' + this.allusers());
        return (
                <div className="row">
                    {
                    this.allusers().map( (user, index)=> {
                            return <UserSinlge key={user._id} user={user} index={index + 1}/>
                            })
                     }

                        
                </div>
                
            )
    }   
};

The problem is when logged in, it only shows the current user's data. All other user objects are not rendered. If I check on the console, console.log('User objects ' + this.allusers()); show objects being rendered 3 times: the first render only shows the current user's data, the second one renders data for all users (the desired result), and the third one again renders only the current user's data.

If I refresh the page, the user data will be rendered properly.

Any idea why?

Answer 1

React calls the render() method of components many times when it's running. If you're experiencing unexpected calls, it's usually the case that something is triggering changes to your component and initiating a re-render. It seems like something might be overwriting the call to Meteor.users.find().fetch() , which is probably happening because you're calling that function on each render. Try inspecting the value outside of the render method or, better yet, rely on tests to ensure that your component is doing what it should be :)

From https://facebook.github.io/react/docs/component-specs.html#render

The render() function should be pure, meaning that it does not modify component state, it returns the same result each time it's invoked, and it does not read from or write to the DOM or otherwise interact with the browser (eg, by using setTimeout). If you need to interact with the browser, perform your work in componentDidMount() or the other lifecycle methods instead. Keeping render() pure makes server rendering more practical and makes components easier to think about.

See also:

• https://facebook.github.io/react/docs/advanced-performance.html
• https://facebook.github.io/react/docs/top-level-api.html#reactdom
• https://ifelse.io/2016/04/04/testing-react-components-with-enzyme-and-mocha/