为什么我不断收到此错误？ 未捕获的类型错误：无法读取 null 的属性（读取“术语”）

Question

this is my code but I keep getting this error

Uncaught TypeError: Cannot read properties of null (reading 'term')

import React from "react";


class SearchBar extends React. Component{
   State = { term: ''};

  onInputChange = event => {
     this.setState({ term: event.target.value});

 };
  onFormSubmit = event => {
    event.preventDefault();
      this.props.onSubmit(this.state.term)
  }

    render(){
        return(
            <div className="Search-bar ui segment ">
                <form  onSubmit={this.onFormSubmit} className="ui form">
                    <div className="field">
                        <label>Video Search</label>
                        <input className="ui input"
                         type="text" 
                         value={this.state.term}
                         onChange={this.onInputChange}
                         />
                    </div>
                </form>
            </div>
        );
    }
}

export default SearchBar;

Answer 1

The proper way to use state in class component is to declare state in the constructor, and use this.setState to modify state.

Also, you need to declare functions not as a variable, but a class instance method and bind them inside the constructor.

The code would be:

import React from 'react';

class SearchBar extends React.component {
  constructor(props) {
    super(props);
    this.state = {
      term: ''
    };
    this.onInputChange = this.onInputChange.bind(this);
    this.onFormSubmit = this.onFormSubmit.bind(this);
  }
  onInputChange(event) {
    this.setState({ term: event.target.value });
  }
  onFormSubmit(event) {
    event.preventDefault();
    this.props.onSubmit(this.state.term);
  }
  render() {
    return (
      <div className="Search-bar ui segment ">
        <form  onSubmit={this.onFormSubmit} className="ui form">
          <div className="field">
            <label>Video Search</label>
            <input className="ui input"
              type="text" 
              value={this.state.term}
              onChange={this.onInputChange}
            />
          </div>
        </form>
      </div>
    );
  }
}
export default SearchBar;