我有一个外部(组件)，可观察对象，我想监听的变化。当对象更新时，它会发出更改事件，然后我希望在检测到任何更改时重新呈现组件。
使用顶级React。渲染这是可能的，但在组件中它不起作用(这是有意义的，因为渲染方法只返回一个对象)。
下面是一个代码示例:
export default class MyComponent extends React.Component {
handleButtonClick() {
this.render();
}
render() {
return (
<div>
{Math.random()}
<button onClick={this.handleButtonClick.bind(this)}>
Click me
</button>
</div>
)
}
}
在内部单击按钮会调用this.render()，但这并不是真正导致呈现发生的原因(您可以在操作中看到这一点，因为由{Math.random()}创建的文本没有改变)。但是，如果我简单地调用this.setState()而不是this.render()，它就可以正常工作。
所以我想我的问题是:React组件需要有状态才能渲染吗?是否有一种方法可以在不改变状态的情况下强制组件按需更新?
在2021年和2022年，这将是强制更新React功能组件的官方方式。
const [, forceUpdate] = useReducer(x => x + 1, 0);
function handleClick() {
forceUpdate();
}
我知道OP是一个类组件。但这个问题是在2015年提出的，现在钩子可用，许多人可能会在功能组件中搜索forceUpdate。这一点是给他们的。
编辑2022年4月18日
强制更新组件通常是不好的做法。
有几个原因可能导致需要使用强制更新。
Not using state variables where you have to - local, redux, context.
The field from the state object you are trying to access and expecting to update/change is too deeply nested in objects or arrays. Even Redux advises to maintain flat objects or arrays. If only one field value changes in a complex object, React may not figure out that the state object has changed, thus it does not update the component. Keep your state flat and simple.
The key on your list items, as mentioned in another answer. In fact, this can cause other unexpected behaviors as well. I've seen lists where items are repeatedly rendered (duplicates) because the keys aren't identical or the keys are just missing altogether. Always request the backend team to send unique ids everywhere possible! Avoid using array indexes for keys. Do not try to create unique ids on the front-end by using nanoid, uuid or random. Because ids created using above methods change each time the component updates (keys provided to a list need to be static and the same on each render). Creating unique ids is usually a backend concern. Try your best to not bring that requirement to the front-end. The front-end's responsibility is only to paint what data the backend returns and not create data on the fly.
If your useEffect, useCallback dependency arrays do not have the proper values set. Use ESLint to help you with this one! Also, this is one of the biggest causes for memory leaks in React. Clean up your state and event listeners in the return callback to avoid memory leaks. Because such memory leaks are awfully difficult to debug.
Always keep an eye on the console. It's your best friend at work. Solving warning and errors that show up in the console can fix a whole lot of nasty things - bugs and issues that you aren't even aware off.
我记得我做错的几件事。万一有用的话…
