React hooks: How do I update state on a nested object with useState()?

问题

I have a component that receives a prop that looks like this:

const styles = {
    font: {
        size: {
            value: '22',
            unit: 'px'
        },
        weight: 'bold',
        color: '#663300',
        family: 'arial',
        align: 'center'
    }
};

I'm trying to update the align property, but when I try to update the object, I wind up replacing the whole object with just the align property.

this is how I'm updating it:

const { ...styling } = styles;
const [style, setStyle] = useState(styling);

return (
        <RadioButtonGroup
            onChange={(event) => {
                setStyle({ ...style, font: { align: event.target.value } });
                console.log(style);
            }}
        />);

When I console.log style I just get {"font":{"align":"left"}} back. I expected to see the whole object with the updated value for align. I'm new to destructuring so what am I doing wrong here?

回答1:

You need to use spread syntax to copy the font object properties too. Also while trying to update current state based on previous, use the callback pattern

<RadioButtonGroup
  onChange={(event) => { 
    setStyle(prevStyle => ({
        ...prevStyle,
        font: { ...prevStyle.font, align: event.target.value }
    }));
    console.log(style);
  }}
/>

回答2:

This is your mistake

setStyle({
    ...style,
    font: { align: event.target.value } // This code replace the font object
});

To preserve the all font object values, you can do like this

const onChange = (event) => {
    const s = {...style};
    s.font.align = event.target.value;
    setStyle(s);
}

const onChange = (event) => {
    setStyle({ 
        ...style,
        font: {
            ...style.font, // Spread the font object to preserve all values
            align: event.target.value
        }
    });
}

回答3:

you can update the styles in this manner

onChange={(event) => {
    const s = {...styles};
    s.font.align = event.target.value;
    setStyle(s);
    console.log(style);
}}

回答4:

If you have multiple values in a nested object, try this method below:

setPost({
  ...post,
  postDetails: {
    ...post.postDetails,
    [event.target.name]: event.target.value,
  },
});

回答5:

Your code for default useState is invalid. You should write like below for default useState:

  const { ...styling } = styles;
  const [style, setStyle] = useState({ styling }); // styling should be use in {}

return (
        <RadioButtonGroup
          onChange={event => {
            setStyle({
              ...styling,
              font: { ...styling.font, align: event.target.value }
            });
            console.log(style);
          }}
        />);

Demo: check this demo with console.log.

回答6:

First: const { ...styling } = styles; is the same as: const styling = styles;

But you may skip that altogether, just use [...] = useState(styles)

setStyle() accepts a function which receives the current state, in your case style. So you may use the spread operator ... to create new object and add values to it.

setStyle(style => ({ ...style, font: { ...style.font, align: event.target.value } ) ) );

Above code uses Arrow function, this could also be written as a normal function, but probably easier to understand:

setStyle( function (style) {
    return  {
        ...style,
        font: {
            ...style.font,
            align: 'center'
        }
    }
});

Your console.log in setStyle displays current style, as changed style will be seen on next render. So I've moved the console.log before return.

const [style, setStyle] = useState(styles);

console.log(style);

return (
        <RadioButtonGroup
            onChange={(event) => {
                setStyle(style => ({ ...style, font: { ...style.font, align: event.target.value } ) ) );
            }}
        />);

Here are some links to help you understand all that:

Spread operator: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax
useState hook: https://reactjs.org/docs/hooks-state.html
Arrow functions: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions

来源：https://stackoverflow.com/questions/56802815/react-hooks-how-do-i-update-state-on-a-nested-object-with-usestate

标签

javascript

reactjs

destructuring