arrays - SetState 在数组中的对象属性上

Question

在我的状态下，我想更新对象数组中第一项的对象属性。对象属性没有改变，即使我正在采取措施确保不变性。

this.state = { 
    myFruits: [{a: false, b: 2, c: 'apple'}, {'a': false, b: 4, c: 'kiwi'}, ...],
    otherCategory: {} 
}

/// further down the code in componentDidUpdate

{ myFruits } = this.state;

let copyFruits = [...myFruits];
let newFruit = { ...copyFruits[0], a : true };
// console.log(newFruit): {a: true, b: 2, c: 'apple'}
copyFruits[0] = newFruit;
// console.log(copyFruits[0)] = {a: true, b: 2, c: 'apple'}
this.setState({ myFruits: copyFruits  });

// the end result is the same as the original state, where the first item, apple, has a : false instead of expected a : true

此更改正在 componentDidUpdate 中进行，我不确定这是否有任何影响。

标签： arraysreactjsobjectstate

Answer 1

我想问题是您的 componetDidUpdate 方法没有被调用。您在这里编写的代码非常好。

class SolutionExample extends React.Component {
constructor(){
    super()
    this.state = { 
myFruits: [{a: false, b: 2, c: 'apple'}, {'a': true, b: 4, c: 'kiwi'}],
otherCategory: {} 
}
}
changeKey =() =>{
    let { myFruits } = this.state;
    let copyFruits = [...myFruits]
    let newFruit = { ...copyFruits[0], a : true };

copyFruits[0] = newFruit;
this.setState({ myFruits: copyFruits  });
}
componentDidUpdate()
    {
        // this method is called whenever the state is changed  }
render() {
    let { myFruits  }  = this.state;
    return (
        <div>

            <h1>Solution</h1>
            {myFruits.map((item) =>{
                if(item.a){
                    return(<h2>{item.b + '-' + item.c}</h2>)
                }   
            })}
            <button onClick={this.changeKey}>Change state</button>
        </div>
    );
}
}

ReactDOM.render(<SolutionExample />, document.getElementById('example')); 

这是链接：https ://codepen.io/anon/pen/pXYdWQ