React.js child state not re-rendering even after calling setState?

Question

I have an app with one child component that I would like to re-render when setState updates the bookInput in the parent's state. I am using axios to request info from google's book api. For some reason, even though the state is updating, the child is not re-rendering. Please help if you can! Thank you!

import React, { Component } from 'react';
import axios from 'axios';

class App extends Component {
  constructor(props) {
    super(props);

    this.state = {
      bookInput: 'ender',
      bookSubmitted: 'initial'
    }

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
    this.handleSubmitEmpty = this.handleSubmitEmpty.bind(this);
  }

    handleChange(e) {
    this.setState({bookInput: e.target.value});
    console.log(this.state.bookInput);
    //this.setState({bookSubmitted: false});
  }

  handleSubmit(e) {
    e.preventDefault();
    //this.setState({bookSubmitted: true})
    const name = this.state.bookInput;
    this.setState({bookInput: name});
    console.log(this.state);
    this.setState({bookSubmitted: 'userSub'});
  }

  handleSubmitEmpty(e) {
    alert('please enter an item to search for');
    e.preventDefault();
  }

  render() {

    return (

      <div className="App">
        <header className = "App-header">
          <h1>Book Search App</h1>
        </header>

        <form className = "form-style" onSubmit = {this.state.bookInput ? this.handleSubmit: this.handleSubmitEmpty}>
          <label>
            <input type="text" className = "input-style" 
              value = {this.state.bookInput} onChange = {this.handleChange}>
            </input>
          </label>
          <button type="submit">search books</button>
        </form>
        {/* <Book bookInput = {this.state.bookInput}/> */}
        {/*this.state.bookSubmitted && <Book bookInput = {this.state.bookInput}/>*/}
        {
          (this.state.bookSubmitted === 'initial' || this.state.bookSubmitted === 'userSub') && 
          <Book bookInput = {this.state.bookInput}/>
        } 
      </div>
    );
  }
}

export default App;


class Book extends Component {
  constructor(props) {
    super(props);

    this.state = {
      //bookInput2: "ender",
      bookTitles: [],
      bookExample: '',
      isLoading: false
    }

    this.bookClick = this.bookClick.bind(this);
  }

  bookClick(book) {
    console.log(book);
    console.log(book.volumeInfo.infoLink);
    const bookURL = book.volumeInfo.infoLink;
    window.open(bookURL);
  }

  componentDidMount() {
    //this.setState({ isLoading: true });
    this.setState({isLoading: true});
    axios.get(`https://www.googleapis.com/books/v1/volumes?q=${this.props.bookInput}`)
      .then((response) => {
        const bookExample1 = response.data.items;
        console.log(bookExample1);
        this.setState({bookTitles: bookExample1, isLoading: false});
      })
      .catch((error) => {
        console.error('ERROR!', error);
        this.setState({isLoading: false});
      });
  }

  render() {
    return (
      <div>
        { this.state.bookTitles ? (
          <div>
            <h2>book list</h2>
            {<ul className = 'list-style'>
              {this.state.isLoading && 
                (<div>
                  loading book list
                </div>)
              }
              {this.state.bookTitles.map(book => (
                <li key={book.id}>
                  <span className = 'book-details book-title' onClick = {() => this.bookClick(book)}> {book.volumeInfo.title}</span>
                  <br/>
                  {book.volumeInfo.imageLinks && 
                    <img src = {book.volumeInfo.imageLinks.thumbnail}/>
                  }
                  { book.volumeInfo.description && 
                    <span className = 'book-details'>{book.volumeInfo.description}</span>
                  }
                  <br/>
                  <span className = 'book-details'>Categories {book.volumeInfo.categories}</span>
                </li>
              ))}
            </ul>}
        </div>) :
        (<p>sorry, that search did not return anything</p>)}
      </div>
    );
  }
}

Answer 1

May be you are looking for something similar to this? https://stackblitz.com/edit/react-snoqkt?file=index.js

The above code can be simplified more and organized but it gives you some idea.

Main changes in the code.

1. Changed Api call from componentDidMount lifecycle event to a new method named getInitialdata which is called in handleSubmit.

   getInitialdata(name){
    axios.get(`https://www.googleapis.com/books/v1/volumes?q=${name}`)
     .then((response) => {
       const bookExample1 = response.data.items;
       console.log(bookExample1);
       this.setState({bookTitles: bookExample1, isLoading: false, bookSubmitted: 'userSub'});
     })
     .catch((error) => {
       console.error('ERROR!', error);
       this.setState({isLoading: false, bookSubmitted: 'userSub'});
     });
   

   }

2. Changed the way how Child component is used.

   <Book bookTitles={this.state.bookTitles} isLoading={this.state.isLoading}/>
   

Issue with your code is you are making an API call in your component's didMount method. This lifecycle event will be invoked only when the component is mounted. Not when it is updated. When you enter some input in your textbox and click on "Search books", componentDidMount event doesnt fire. And this is the reason why API calls are not happening from the second time.

More on the lifecycle events at https://reactjs.org/docs/react-component.html#componentdidmount

Answer 2

I've taken your code and extrapolated it into this sandbox. Just as you said, your parent component state is updating as it should, but the problem is that the child component doesn't change its state.

A state change will always trigger a re-render in React. The only problem is, your child component is managing it's own state, which isn't directly changing. Instead, it's just receiving new props again and again, but not doing anything with them.

If you look at your code for the <Book /> component, you only modify its state on componentDidMount, which only happens once. If you'd like to programmatically make it update, you can do one of two things.

1. Remove state from the child component, and make it rely entirely on props, so that it stays in sync with the parent
2. Use the componentDidUpdate lifecycle method (docs) to choose when to change the state of the child (which will trigger the re-render)