How to toggle boolean state of react component?

问题

I'd like to know how to toggle a boolean state of a react component. For instance:

I have boolean state check in the constructor of my component:

constructor(props, context) { 
   super(props, context);

   this.state = {
      check: false
   };
};

I am trying to toggle the state each time my checkbox is clicked, using the this.setState method:

<label><input type=checkbox" value="check" onChange = {(e) => this.setState({check: !check.value})}/> Checkbox </label>

Of course I get a Uncaught ReferenceError: check is not defined. So how can I achieve this?

Many thanks in advance.

回答1:

Since nobody posted this, I am posting the correct answer. If your new state update depends on the previous state, always use the functional form of setState which accepts as argument a function that returns a new state.

In your case:

this.setState(prevState => ({
  check: !prevState.check
}));

See docs

回答2:

You should use this.state.check instead of check.value here:

this.setState({check: !this.state.check})

But anyway it is bad practice to do it this way. Much better to move it to separate method and don't write callbacks directly in markup.

回答3:

Use checked to get the value. During onChange, checked will be true and it will be a type of boolean.

Hope this helps!

class A extends React.Component {
  constructor() {
    super()
    this.handleCheckBox = this.handleCheckBox.bind(this)
    this.state = {
      checked: false
    }
  }
  
  handleCheckBox(e) {
    this.setState({
      checked: e.target.checked
    })
  }
  
  render(){
    return <input type="checkbox" onChange={this.handleCheckBox} checked={this.state.checked} />
  }
}

ReactDOM.render(<A/>, document.getElementById('app'))

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

回答4:

Try:

<label><input type=checkbox" value="check" onChange = {(e) => this.setState({check: !this.state.check.value})}/> Checkbox </label>

Using check: !check.value means it is looking for the check object, which you haven't declared.

You need to specify that you want the opposite value of this.state.check.

回答5:

Depending on your context; this will allow you to update state given the mouseEnter function. Either way, by setting a state value to either true:false you can update that state value given any function by setting it to the opposing value with !this.state.variable

state = {
  hover: false
}

onMouseEnter = () => {
  this.setState({
    hover: !this.state.hover
  });
};

回答6:

You could also use React's useState hook to declare local state for a function component. The initial state of the variable toggled has been passed as an argument to the method .useState.

import { render } from 'react-dom';
import React from "react";

type Props = {
  text: string,
  onClick(event: React.MouseEvent<HTMLButtonElement>): void,
};

export function HelloWorldButton(props: Props) {
  const [toggled, setToggled] = React.useState(false); // returns a stateful value, and a function to update it
  return <button
  onClick={(event) => {
    setToggled(!toggled);
    props.onClick(event);
  }}
  >{props.text} (toggled: {toggled.toString()})</button>;
}


render(<HelloWorldButton text='Hello World' onClick={() => console.log('clicked!')} />, document.getElementById('root'));

https://stackblitz.com/edit/react-ts-qga3vc

回答7:

I found this the most simple when toggling boolean values. Simply put if the value is already true then it sets it to false and vice versa. Beware of undefined errors, make sure your property was defined before executing

this.setState({
   propertyName: this.propertyName = !this.propertyName
});

回答8:

Here's an example using hooks (requires React >= 16.8.0)

// import React, { useState } from 'react';
const { useState } = React;

function App() {
  const [checked, setChecked] = useState(false);
  const toggleChecked = () => setChecked(value => !value);
  return (
    <input
      type="checkbox"
      checked={checked}
      onChange={toggleChecked}
    />
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

<script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>

<div id="root"><div>

回答9:

I was landed in this page when I am searching to use toggle state in React component using Redux but I don't find here any approach using the same.

So, I think it might help someone who was struggling to implement toggle state using Redux.

My reducer file goes here. I get the initial state false by default.

const INITIAL_STATE = { popup: false };
export default (state = INITIAL_STATE, action) => {
    switch (action.type) {
        case "POPUP":
            return {
                ...state,
                popup: action.value
            };
        default:
            return state;
    }
    return state;
};

I change state on clicking the image. So, my img tag goes here with onClick function.

<img onClick={togglePopup} src={props.currentUser.image} className="avatar-image avatar-image--icon" />

My Toggle Popup function goes below, which call Dispatcher.

const togglePopup = ev => {
    ev.preventDefault();
    props.handlePopup(!props.popup);
};

This call goes to below mapDispatchToProps function which reflects back the toggled state.

const mapDispatchToProps = dispatch => ({
    handlePopup: value => dispatch({ type: "POPUP", value })
});

Thank you.

来源：https://stackoverflow.com/questions/40359800/how-to-toggle-boolean-state-of-react-component

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