为什么我的 onClick 在渲染时被调用？ - 反应.js

Question

I have a component that I have created:

class Create extends Component {
  constructor(props) {
    super(props);
  }

  render() {
    var playlistDOM = this.renderPlaylists(this.props.playlists);
    return (
      <div>
        {playlistDOM}
      </div>
    )
  }

  activatePlaylist(playlistId) {
    debugger;
  }

  renderPlaylists(playlists) {
    return playlists.map(playlist => {
      return <div key={playlist.playlist_id} onClick={this.activatePlaylist(playlist.playlist_id)}>{playlist.playlist_name}</div>
    });
  }
}

function mapStateToProps(state) {
  return {
    playlists: state.playlists
  }
}

export default connect(mapStateToProps)(Create);

When I render this page, activatePlaylist is called for each playlist in my map . If I bind activatePlaylist like:

activatePlaylist.bind(this, playlist.playlist_id)

I can also use an anonymous function:

onClick={() => this.activatePlaylist(playlist.playlist_id)}

then it works as expected. Why does this happen?

Answer 1

You need pass to onClick reference to function, when you do like this activatePlaylist( .. ) you call function and pass to onClick value that returned from activatePlaylist . You can use one of these three options:

1 . using .bind

activatePlaylist.bind(this, playlist.playlist_id)

2 . using arrow function

onClick={ () => this.activatePlaylist(playlist.playlist_id) }

3 . or return function from activatePlaylist

activatePlaylist(playlistId) {
  return function () {
     // you code 
  }
}

Answer 2

I know this post is a few years old already, but just to reference the latest React tutorial/documentation about this common mistake (I made it too) from https://reactjs.org/tutorial/tutorial.html :

Note

To save typing and avoid the confusing behavior of this, we will use the arrow function syntax for event handlers here and further below:

class Square extends React.Component {
 render() {
   return (
     <button className="square" onClick={() => alert('click')}>
       {this.props.value}
     </button>
   );
 }
}

Notice how with onClick={() => alert('click')}, we're passing a function as the onClick prop. React will only call this function after a click. Forgetting () => and writing onClick={alert('click')} is a common mistake, and would fire the alert every time the component re-renders.

Answer 3

This behaviour was documented when React announced the release of class based components.

https://facebook.github.io/react/blog/2015/01/27/react-v0.13.0-beta-1.html

Autobinding

React.createClass has a built-in magic feature that bound all methods to this automatically for you. This can be a little confusing for JavaScript developers that are not used to this feature in other classes, or it can be confusing when they move from React to other classes.

Therefore we decided not to have this built-in into React's class model. You can still explicitly prebind methods in your constructor if you want.

Answer 4

The way you passing the method this.activatePlaylist(playlist.playlist_id) , will call the method immediately. You should pass the reference of the method to the onClick event. Follow one of the below-mentioned implementation to resolve your problem.

1.

onClick={ (event) => { this.activatePlaylist.(playlist.playlist_id)}}

Here bind property is used to create a reference of the this.activatePlaylist method by passing this context and argument playlist.playlist_id

2.

 onClick={ (event) => { this.activatePlaylist.(playlist.playlist_id)}}

This will attach a function to the onClick event which will get triggered on user click action only. When this code exectues the this.activatePlaylist method will be called.

Answer 5

import React from 'react';
import { Page ,Navbar, Popup} from 'framework7-react';

class AssignmentDashboard extends React.Component {
    constructor(props) {
      super(props);
      this.state = {

    }

    
      onSelectList=(ProjectId)=>{
          return(

            console.log(ProjectId,"projectid")
          )

      }
            
render() {
       
    return (   
      
 <li key={index} onClick={()=> this.onSelectList(item.ProjectId)}></li>
                       
                       )}