Sometimes, you want the state of two components to always change together. To do it, remove state from both of them, move it to their closest common parent, and then pass it down to them via props. This is known as lifting state up, and it’s one of the most common things you will do writing React code. 有时候，你希望两个组件的状态始终同步更改。要实现这一点，可以将相关 state 从这两个组件上移除，并把 state 放到它们的公共父级，再通过 props 将 state 传递给这两个组件。这被称为“状态提升”，这是编写 React 代码时常做的事。
你将会学习到
- How to share state between components by lifting it up
- 如何使用状态提升在组件之间共享状态
- What are controlled and uncontrolled components
- 什么是受控组件和非受控组件
举例说明一下状态提升 | Lifting state up by example
In this example, a parent Accordion component renders two separate Panels:
在这个例子中，父组件 Accordion 渲染了 2 个独立的 Panel 组件。
AccordionPanelPanel
Each Panel component has a boolean isActive state that determines whether its content is visible.
每个 Panel 组件都有一个布尔值 isActive，用于控制其内容是否可见。
Press the Show button for both panels: 请点击 2 个面板中的显示按钮：
import { useState } from 'react'; function Panel({ title, children }) { const [isActive, setIsActive] = useState(false); return ( <section className="panel"> <h3>{title}</h3> {isActive ? ( <p>{children}</p> ) : ( <button onClick={() => setIsActive(true)}> 显示 </button> )} </section> ); } export default function Accordion() { return ( <> <h2>哈萨克斯坦，阿拉木图</h2> <Panel title="关于"> 阿拉木图人口约200万，是哈萨克斯坦最大的城市。它在 1929 年到 1997 年间都是首都。 </Panel> <Panel title="词源"> 这个名字来自于 <span lang="kk-KZ">алма</span>，哈萨克语中“苹果”的意思，经常被翻译成“苹果之乡”。事实上，阿拉木图的周边地区被认为是苹果的发源地，<i lang="la">Malus sieversii</i> 被认为是现今苹果的祖先。 </Panel> </> ); }
Notice how pressing one panel’s button does not affect the other panel—they are independent. 我们发现点击其中一个面板中的按钮并不会影响另外一个，他们是独立的。
Initially, each Panel’s isActive state is false, so they both appear collapsed
由于一开始所有 Panel 内部的 isActive 都是 false，因此它们的内容都不会显示。
Clicking either Panel’s button will only update that Panel’s isActive state alone
此时，点击任意一个 Panel 组件中的按钮都只会更新当前 Panel 组件内的 isActive 值
But now let’s say you want to change it so that only one panel is expanded at any given time. With that design, expanding the second panel should collapse the first one. How would you do that? 假设现在你想改变这种行为，以便在任何时候只展开一个面板。在这种设计下，展开第 2 个面板应会折叠第 1 个面板。你该如何做到这一点呢？“
To coordinate these two panels, you need to “lift their state up” to a parent component in three steps: 要协调好这两个面板，我们需要分 3 步将状态“提升”到他们的父组件中。
- Remove state from the child components.
- 从子组件中 移除 state 。
- Pass hardcoded data from the common parent.
- 从父组件 传递 硬编码数据。
- Add state to the common parent and pass it down together with the event handlers.
- 为共同的父组件添加 state ，并将其与事件处理函数一起向下传递。
This will allow the Accordion component to coordinate both Panels and only expand one at a time.
这样，Accordion 组件就可以控制 2 个 Panel 组件，保证同一时间只能展开一个。
第 1 步: 从子组件中移除状态 | Step 1: Remove state from the child components
You will give control of the Panel’s isActive to its parent component. This means that the parent component will pass isActive to Panel as a prop instead. Start by removing this line from the Panel component:
你将把 Panel 组件对 isActive 的控制权交给他们的父组件。这意味着，父组件会将 isActive 作为 prop 传给子组件 Panel。我们先从 Panel 组件中 删除下面这一行：
const [isActive, setIsActive] = useState(false);And instead, add isActive to the Panel’s list of props:
然后，把 isActive 加入 Panel 组件的 props 中：
function Panel({ title, children, isActive }) {Now the Panel’s parent component can control isActive by passing it down as a prop. Conversely, the Panel component now has no control over the value of isActive—it’s now up to the parent component!
现在 Panel 的父组件就可以通过 向下传递 prop 来 控制 isActive。但相反地，Panel 组件对 isActive 的值 没有控制权 —— 现在完全由父组件决定！
第 2 步: 从公共父组件传递硬编码数据 | Step 2: Pass hardcoded data from the common parent
To lift state up, you must locate the closest common parent component of both of the child components that you want to coordinate: 为了实现状态提升，必须定位到你想协调的 两个 子组件最近的公共父组件：
Accordion(最近的公共父组件) | (closest common parent)PanelPanel
In this example, it’s the Accordion component. Since it’s above both panels and can control their props, it will become the “source of truth” for which panel is currently active. Make the Accordion component pass a hardcoded value of isActive (for example, true) to both panels:
在这个例子中，公共父组件是 Accordion。因为它位于两个面板之上，可以控制它们的 props，所以它将成为当前激活面板的“控制之源”。通过 Accordion 组件将硬编码值 isActive（例如 true ）传递给两个面板：
import { useState } from 'react'; export default function Accordion() { return ( <> <h2>哈萨克斯坦，阿拉木图</h2> <Panel title="关于" isActive={true}> 阿拉木图人口约200万，是哈萨克斯坦最大的城市。它在 1929 年到 1997 年间都是首都。 </Panel> <Panel title="词源" isActive={true}> 这个名字来自于 <span lang="kk-KZ">алма</span>，哈萨克语中“苹果”的意思，经常被翻译成“苹果之乡”。事实上，阿拉木图的周边地区被认为是苹果的发源地，<i lang="la">Malus sieversii</i> 被认为是现今苹果的祖先。 </Panel> </> ); } function Panel({ title, children, isActive }) { return ( <section className="panel"> <h3>{title}</h3> {isActive ? ( <p>{children}</p> ) : ( <button onClick={() => setIsActive(true)}> 显示 </button> )} </section> ); }
Try editing the hardcoded isActive values in the Accordion component and see the result on the screen.
你可以尝试修改 Accordion 组件中 isActive 的值，并在屏幕上查看结果。
第 3 步: 为公共父组件添加状态 | Step 3: Add state to the common parent
Lifting state up often changes the nature of what you’re storing as state. 状态提升通常会改变原状态的数据存储类型。
In this case, only one panel should be active at a time. This means that the Accordion common parent component needs to keep track of which panel is the active one. Instead of a boolean value, it could use a number as the index of the active Panel for the state variable:
在这个例子中，一次只能激活一个面板。这意味着 Accordion 这个父组件需要记录 哪个 面板是被激活的面板。我们可以用数字作为当前被激活 Panel 的索引，而不是 boolean 值：
const [activeIndex, setActiveIndex] = useState(0);When the activeIndex is 0, the first panel is active, and when it’s 1, it’s the second one.
当 activeIndex 为 0 时，激活第一个面板，为 1 时，激活第二个面板。
Clicking the “Show” button in either Panel needs to change the active index in Accordion. A Panel can’t set the activeIndex state directly because it’s defined inside the Accordion. The Accordion component needs to explicitly allow the Panel component to change its state by passing an event handler down as a prop:
在任意一个 Panel 中点击“显示”按钮都需要更改 Accordion 中的激活索引值。 Panel 中无法直接设置状态 activeIndex 的值，因为该状态是在 Accordion 组件内部定义的。 Accordion 组件需要 显式允许 Panel 组件通过 将事件处理程序作为 prop 向下传递 来更改其状态：
<>
<Panel
isActive={activeIndex === 0}
onShow={() => setActiveIndex(0)}
>
...
</Panel>
<Panel
isActive={activeIndex === 1}
onShow={() => setActiveIndex(1)}
>
...
</Panel>
</>The <button> inside the Panel will now use the onShow prop as its click event handler:
现在 Panel 组件中的 <button> 将使用 onShow 这个属性作为其点击事件的处理程序：
import { useState } from 'react'; export default function Accordion() { const [activeIndex, setActiveIndex] = useState(0); return ( <> <h2>哈萨克斯坦，阿拉木图</h2> <Panel title="关于" isActive={activeIndex === 0} onShow={() => setActiveIndex(0)} > 阿拉木图人口约200万，是哈萨克斯坦最大的城市。它在 1929 年到 1997 年间都是首都。 </Panel> <Panel title="词源" isActive={activeIndex === 1} onShow={() => setActiveIndex(1)} > 这个名字来自于 <span lang="kk-KZ">алма</span>，哈萨克语中“苹果”的意思，经常被翻译成“苹果之乡”。事实上，阿拉木图的周边地区被认为是苹果的发源地，<i lang="la">Malus sieversii</i> 被认为是现今苹果的祖先。 </Panel> </> ); } function Panel({ title, children, isActive, onShow }) { return ( <section className="panel"> <h3>{title}</h3> {isActive ? ( <p>{children}</p> ) : ( <button onClick={onShow}> 显示 </button> )} </section> ); }
This completes lifting state up! Moving state into the common parent component allowed you to coordinate the two panels. Using the active index instead of two “is shown” flags ensured that only one panel is active at a given time. And passing down the event handler to the child allowed the child to change the parent’s state.
这样，我们就完成了对状态的提升！将状态移至公共父组件中可以让你更好的管理这两个面板。使用激活索引值代替之前的 是否显示 标识确保了一次只能激活一个面板。而通过向下传递事件处理函数可以让子组件修改父组件的状态。
Initially, Accordion’s activeIndex is 0, so the first Panel receives isActive = true
一开始, Accordion 组件中的 activeIndex 是 0，此时第一个 Panel 组件接受到的属性为 isActive = true
When Accordion’s activeIndex state changes to 1, the second Panel receives isActive = true instead
当 Accordion 组件中的 activeIndex 变为 1 时，第二个 Panel 组件接受到的属性变为 isActive = true，第一个 Panel 组件接受到的属性变为 isActive = false
深入探讨
It is common to call a component with some local state “uncontrolled”. For example, the original Panel component with an isActive state variable is uncontrolled because its parent cannot influence whether the panel is active or not.
通常我们把包含“不受控制”状态的组件称为“非受控组件”。例如，最开始带有 isActive 状态变量的 Panel 组件就是不受控制的，因为其父组件无法控制面板的激活状态。
In contrast, you might say a component is “controlled” when the important information in it is driven by props rather than its own local state. This lets the parent component fully specify its behavior. The final Panel component with the isActive prop is controlled by the Accordion component.
相反，当组件中的重要信息是由 props 而不是其自身状态驱动时，就可以认为该组件是“受控组件”。这就允许父组件完全指定其行为。最后带有 isActive 属性的 Panel 组件是由 Accordion 组件控制的。
Uncontrolled components are easier to use within their parents because they require less configuration. But they’re less flexible when you want to coordinate them together. Controlled components are maximally flexible, but they require the parent components to fully configure them with props.
非受控组件通常很简单，因为它们不需要太多配置。但是当你想把它们组合在一起使用时，就不那么灵活了。受控组件具有最大的灵活性，但它们需要父组件使用 props 对其进行配置。
In practice, “controlled” and “uncontrolled” aren’t strict technical terms—each component usually has some mix of both local state and props. However, this is a useful way to talk about how components are designed and what capabilities they offer.
在实践中，“受控”和“非受控”并不是严格的技术术语——通常每个组件都同时拥有内部状态和 props。然而，这对于组件该如何设计和提供什么样功能的讨论是有帮助的。
When writing a component, consider which information in it should be controlled (via props), and which information should be uncontrolled (via state). But you can always change your mind and refactor later.
当编写一个组件时，你应该考虑哪些信息应该受控制（通过 props），哪些信息不应该受控制（通过 state）。当然，你可以随时改变主意并重构代码。
每个状态都对应唯一的数据源 | A single source of truth for each state
In a React application, many components will have their own state. Some state may “live” close to the leaf components (components at the bottom of the tree) like inputs. Other state may “live” closer to the top of the app. For example, even client-side routing libraries are usually implemented by storing the current route in the React state, and passing it down by props!
在 React 应用中，很多组件都有自己的状态。一些状态可能“活跃”在叶子组件（树形结构最底层的组件）附近，例如输入框。另一些状态可能在应用程序顶部“活动”。例如，客户端路由库也是通过将当前路由存储在 React 状态中，利用 props 将状态层层传递下去来实现的！
For each unique piece of state, you will choose the component that “owns” it. This principle is also known as having a “single source of truth”. It doesn’t mean that all state lives in one place—but that for each piece of state, there is a specific component that holds that piece of information. Instead of duplicating shared state between components, lift it up to their common shared parent, and pass it down to the children that need it. 对于每个独特的状态，都应该存在且只存在于一个指定的组件中作为 state。这一原则也被称为拥有 “可信单一数据源”。它并不意味着所有状态都存在一个地方——对每个状态来说，都需要一个特定的组件来保存这些状态信息。你应该 将状态提升 到公共父级，或 将状态传递 到需要它的子级中，而不是在组件之间复制共享的状态。
Your app will change as you work on it. It is common that you will move state down or back up while you’re still figuring out where each piece of the state “lives”. This is all part of the process! 你的应用会随着你的操作而变化。当你将状态上下移动时，你依然会想要确定每个状态在哪里“活跃”。这都是过程的一部分！
To see what this feels like in practice with a few more components, read Thinking in React. 想了解在更多组件中的实践，请阅读 React 思维.
摘要
- When you want to coordinate two components, move their state to their common parent.
- 当你想要整合两个组件时，将它们的 state 移动到共同的父组件中。
- Then pass the information down through props from their common parent.
- 然后在父组件中通过
props把信息传递下去。 - Finally, pass the event handlers down so that the children can change the parent’s state.
- 最后，向下传递事件处理程序，以便子组件可以改变父组件的 state 。
- It’s useful to consider components as “controlled” (driven by props) or “uncontrolled” (driven by state).
- 考虑该将组件视为“受控”（由 prop 驱动）或是“不受控”（由 state 驱动）是十分有益的。
第 1 个挑战 共 2 个挑战: 同步输入状态 | Synced inputs
These two inputs are independent. Make them stay in sync: editing one input should update the other input with the same text, and vice versa. 现在有两个独立的输入框。为了让它们保持同步：即编辑一个输入框时，另一个输入框也会更新相同的文本，反之亦然。
import { useState } from 'react'; export default function SyncedInputs() { return ( <> <Input label="第一个输入框" /> <Input label="第二个输入框" /> </> ); } function Input({ label }) { const [text, setText] = useState(''); function handleChange(e) { setText(e.target.value); } return ( <label> {label} {' '} <input value={text} onChange={handleChange} /> </label> ); }