React Hooks(useState)中的推送方法?

2022-01-31 00:00:00 reactjs javascript react-hooks

如何在 useState 数组 React 钩子中推送元素?这是反应状态下的旧方法吗?还是新的东西?

How to push element inside useState array React hook? Is that as an old method in react state? Or something new?

例如setState 推送示例 ?

推荐答案

当你使用 useState，可以获取状态项的更新方法:

When you use useState, you can get an update method for the state item:

const [theArray, setTheArray] = useState(initialArray);

然后，当您想添加一个新元素时，您可以使用该函数并传入新数组或将创建新数组的函数.通常是后者，因为状态更新是异步的，有时是批处理的:

then, when you want to add a new element, you use that function and pass in the new array or a function that will create the new array. Normally the latter, since state updates are asynchronous and sometimes batched:

setTheArray(oldArray => [...oldArray, newElement]);

如果您仅为某些特定的用户事件(如 click(但不像 鼠标移动):

Sometimes you can get away without using that callback form, if you only update the array in handlers for certain specific user events like click (but not like mousemove):

setTheArray([...theArray, newElement]);

React 确保刷新渲染的事件是离散事件".此处列出.

The events for which React ensures that rendering is flushed are the "discrete events" listed here.

实时示例(将回调传递给 setTheArray):

Live Example (passing a callback into setTheArray):

const {useState, useCallback} = React;
function Example() {
    const [theArray, setTheArray] = useState([]);
    const addEntryClick = () => {
        setTheArray(oldArray => [...oldArray, `Entry ${oldArray.length}`]);
    };
    return [
        <input type="button" onClick={addEntryClick} value="Add" />,
        <div>{theArray.map(entry =>
          <div>{entry}</div>
        )}
        </div>
    ];
}

ReactDOM.render(
    <Example />,
    document.getElementById("root")
);

<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.1/umd/react-dom.production.min.js"></script>

因为对 theArray 的唯一更新是 click 事件(离散"事件之一)中的更新，所以我可以直接使用在 addEntry 中更新:

Because the only update to theArray in there is the one in a click event (one of the "discrete" events), I could get away with a direct update in addEntry:

const {useState, useCallback} = React;
function Example() {
    const [theArray, setTheArray] = useState([]);
    const addEntryClick = () => {
        setTheArray([...theArray, `Entry ${theArray.length}`]);
    };
    return [
        <input type="button" onClick={addEntryClick} value="Add" />,
        <div>{theArray.map(entry =>
          <div>{entry}</div>
        )}
        </div>
    ];
}

ReactDOM.render(
    <Example />,
    document.getElementById("root")
);

<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.1/umd/react-dom.production.min.js"></script>

相关文章