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Expand Up @@ -4,25 +4,25 @@ title: Render Props
permalink: docs/render-props.html
---

The term ["render prop"](https://cdb.reacttraining.com/use-a-render-prop-50de598f11ce) refers to a technique for sharing code between React components using a prop whose value is a function.
术语 ["render prop"](https://cdb.reacttraining.com/use-a-render-prop-50de598f11ce) 是指一种在 React 组件之间使用一个值为函数的 prop 共享代码的简单技术

A component with a render prop takes a function that returns a React element and calls it instead of implementing its own render logic.
具有 render prop 的组件接受一个函数，该函数返回一个 React 元素并调用它而不是实现自己的渲染逻辑。

```jsx
<DataProvider render={data => (
<h1>Hello {data.target}</h1>
)}/>
```

Libraries that use render props include [React Router](https://reacttraining.com/react-router/web/api/Route/render-func) and [Downshift](https://github.com/paypal/downshift).
使用 render prop 的库有 [React Router](https://reacttraining.com/react-router/web/api/Route/render-func) 和 [Downshift](https://github.com/paypal/downshift).

In this document, we’ll discuss why render props are useful, and how to write your own.
在这个文档中，我们将讨论为什么 render prop 是有用的，以及如何写一个自己的 render prop 组件。

## Use Render Props for Cross-Cutting Concerns {#use-render-props-for-cross-cutting-concerns}
## 使用 Render Props 解决来横切关注点（Cross-Cutting Concerns） {#use-render-props-for-cross-cutting-concerns}

Components are the primary unit of code reuse in React, but it's not always obvious how to share the state or behavior that one component encapsulates to other components that need that same state.
组件是 React 代码复用的主要单元，但如何分享一个组件封装到其他需要相同 state 组件的状态或行为并不总是很容易。

For example, the following component tracks the mouse position in a web app:
例如，以下组件跟踪 Web 应用程序中的鼠标位置：

```js
class MouseTracker extends React.Component {
Expand All @@ -42,22 +42,22 @@ class MouseTracker extends React.Component {
render() {
return (
<div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>
<h1>Move the mouse around!</h1>
<p>The current mouse position is ({this.state.x}, {this.state.y})</p>
<h1>移动鼠标!</h1>
<p>当前的鼠标位置是 ({this.state.x}, {this.state.y})</p>
</div>
);
}
}
```

As the cursor moves around the screen, the component displays its (x, y) coordinates in a `<p>`.
当光标在屏幕上移动时，组件在 `<p>` 中显示其（x，y）坐标。

Now the question is: How can we reuse this behavior in another component? In other words, if another component needs to know about the cursor position, can we encapsulate that behavior so that we can easily share it with that component?
现在的问题是：我们如何在另一个组件中复用这个行为？换个说法，若另一个组件需要知道鼠标位置，我们能否封装这一行为，以便轻松地与其他组件共享它？？

Since components are the basic unit of code reuse in React, let's try refactoring the code a bit to use a `<Mouse>` component that encapsulates the behavior we need to reuse elsewhere.
由于组件是 React 中最基础的代码复用单元，现在尝试重构一部分代码使其能够在 `<Mouse>` 组件中封装我们需要共享的行为。

```js
// The <Mouse> component encapsulates the behavior we need...
// <Mouse> 组件封装了我们需要的行为...
class Mouse extends React.Component {
constructor(props) {
super(props);
Expand All @@ -76,7 +76,7 @@ class Mouse extends React.Component {
return (
<div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>

{/* ...but how do we render something other than a <p>? */}
{/* ...但我们如何渲染 <p> 以外的东西? */}
<p>The current mouse position is ({this.state.x}, {this.state.y})</p>
</div>
);
Expand All @@ -87,19 +87,19 @@ class MouseTracker extends React.Component {
render() {
return (
<div>
<h1>Move the mouse around!</h1>
<h1>移动鼠标!</h1>
<Mouse />
</div>
);
}
}
```

Now the `<Mouse>` component encapsulates all behavior associated with listening for `mousemove` events and storing the (x, y) position of the cursor, but it's not yet truly reusable.
现在 `<Mouse>` 组件封装了所有关于监听 `mousemove` 事件和存储鼠标 (x, y) 位置的行为，但其仍不是真正的可复用。

For example, let's say we have a `<Cat>` component that renders the image of a cat chasing the mouse around the screen. We might use a `<Cat mouse={{ x, y }}>` prop to tell the component the coordinates of the mouse so it knows where to position the image on the screen.
举个例子，假设我们有一个 <Cat> 组件，它可以呈现一张在屏幕上追逐鼠标的猫的图片。我们或许会使用 `<Cat mouse={{ x, y }}` prop 来告诉组件鼠标的坐标以让它知道图片应该在屏幕哪个位置。

As a first pass, you might try rendering the `<Cat>` *inside `<Mouse>`'s `render` method*, like this:
首先, 你或许会像这样，尝试在 `<Mouse>` 内部的渲染方法渲染 `<Cat>` 组件：:

```js
class Cat extends React.Component {
Expand Down Expand Up @@ -130,10 +130,9 @@ class MouseWithCat extends React.Component {
<div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>

{/*
We could just swap out the <p> for a <Cat> here ... but then
we would need to create a separate <MouseWithSomethingElse>
component every time we need to use it, so <MouseWithCat>
isn't really reusable yet.
我们可以在这里换掉 <p> 的 <Cat> ......
但是接着我们需要创建一个单独的 <MouseWithSomethingElse>
每次我们需要使用它时，<MouseWithCat> 是不是真的可以重复使用.
*/}
<Cat mouse={this.state} />
</div>
Expand All @@ -145,17 +144,17 @@ class MouseTracker extends React.Component {
render() {
return (
<div>
<h1>Move the mouse around!</h1>
<h1>移动鼠标!</h1>
<MouseWithCat />
</div>
);
}
}
```

This approach will work for our specific use case, but we haven't achieved the objective of truly encapsulating the behavior in a reusable way. Now, every time we want the mouse position for a different use case, we have to create a new component (i.e. essentially another `<MouseWithCat>`) that renders something specifically for that use case.
这种方法适用于我们的特定用例，但我们还没有达到以可复用的方式真正封装行为的目标。现在，每当我们想要鼠标位置用于不同的用例时，我们必须创建一个新的组件（本质上是另一个 `<MouseWithCat>` ），它专门为该用例呈现一些东西.

Here's where the render prop comes in: Instead of hard-coding a `<Cat>` inside a `<Mouse>` component, and effectively changing its rendered output, we can provide `<Mouse>` with a function prop that it uses to dynamically determine what to render–a render prop.
这也是 render prop 的来历：我们可以提供一个带有函数 prop 的 `<Mouse>` 组件，它能够动态决定什么需要渲染的，而不是将 `<Cat>` 硬编码到 `<Mouse>` 组件里，并有效地改变它的渲染结果。

```js
class Cat extends React.Component {
Expand Down Expand Up @@ -199,7 +198,7 @@ class MouseTracker extends React.Component {
render() {
return (
<div>
<h1>Move the mouse around!</h1>
<h1>移动鼠标!</h1>
<Mouse render={mouse => (
<Cat mouse={mouse} />
)}/>
Expand All @@ -209,17 +208,17 @@ class MouseTracker extends React.Component {
}
```

Now, instead of effectively cloning the `<Mouse>` component and hard-coding something else in its `render` method to solve for a specific use case, we provide a `render` prop that `<Mouse>` can use to dynamically determine what it renders.
现在，我们提供了一个 `render` 方法 让 `<Mouse>` 能够动态决定什么需要渲染，而不是克隆 `<Mouse>` 组件然后硬编码来解决特定的用例。

More concretely, **a render prop is a function prop that a component uses to know what to render.**
更具体地说，**render prop 是一个用于告知组件需要渲染什么内容的函数 prop。**

This technique makes the behavior that we need to share extremely portable. To get that behavior, render a `<Mouse>` with a `render` prop that tells it what to render with the current (x, y) of the cursor.
这项技术使我们共享行为非常容易。要获得这个行为，只要渲染一个带有 `render` prop 的 `<Mouse>` 组件就能够告诉它当前鼠标坐标 (x, y) 要渲染什么。

One interesting thing to note about render props is that you can implement most [higher-order components](/docs/higher-order-components.html) (HOC) using a regular component with a render prop. For example, if you would prefer to have a `withMouse` HOC instead of a `<Mouse>` component, you could easily create one using a regular `<Mouse>` with a render prop:
关于 render prop 一个有趣的事情是你可以使用带有 render prop 的常规组件来实现大多数[高阶组件](/docs/higher-order-components.html) (HOC)。 例如，如果你更喜欢使用 `withMouse` HOC而不是 `<Mouse>` 组件，你可以使用带有 render prop 的常规 `<Mouse>` 轻松创建一个：

```js
// If you really want a HOC for some reason, you can easily
// create one using a regular component with a render prop!
// 如果你出于某种原因真的想要 HOC，那么你可以轻松实现
// 使用具有 render prop 的普通组件创建一个！
function withMouse(Component) {
return class extends React.Component {
render() {
Expand All @@ -233,51 +232,51 @@ function withMouse(Component) {
}
```

So using a render prop makes it possible to use either pattern.
因此，你可以将任一模式与 render prop 一起使用。

## Using Props Other Than `render` {#using-props-other-than-render}
## 使用 Props 而非 `render` {#using-props-other-than-render}

It's important to remember that just because the pattern is called "render props" you don't *have to use a prop named `render` to use this pattern*. In fact, [*any* prop that is a function that a component uses to know what to render is technically a "render prop"](https://cdb.reacttraining.com/use-a-render-prop-50de598f11ce).
重要的是要记住，render prop 是因为模式才被称为 *render* prop ，你不一定要用名为 `render` 的 prop 来使用这种模式。事实上， [*任何*被用于告知组件需要渲染什么内容的函数 prop 在技术上都可以被称为 “render prop”](https://cdb.reacttraining.com/use-a-render-prop-50de598f11ce).

Although the examples above use `render`, we could just as easily use the `children` prop!
尽管之前的例子使用了 `render`，我们也可以简单地使用 `children` prop！

```js
<Mouse children={mouse => (
<p>The mouse position is {mouse.x}, {mouse.y}</p>
<p>鼠标的位置是 {mouse.x}，{mouse.y}</p>
)}/>
```

And remember, the `children` prop doesn't actually need to be named in the list of "attributes" in your JSX element. Instead, you can put it directly *inside* the element!
记住，`children` prop 并不真正需要添加到 JSX 元素的 “attributes” 列表中。相反，你可以直接放置到元素的*内部*！

```js
<Mouse>
{mouse => (
<p>The mouse position is {mouse.x}, {mouse.y}</p>
<p>鼠标的位置是 {mouse.x}，{mouse.y}</p>
)}
</Mouse>
```

You'll see this technique used in the [react-motion](https://github.com/chenglou/react-motion) API.
你将在 [react-motion](https://github.com/chenglou/react-motion) 的 API 中看到此技术。

Since this technique is a little unusual, you'll probably want to explicitly state that `children` should be a function in your `propTypes` when designing an API like this.
由于这一技术的特殊性，当你在设计一个类似的 API 时，你或许会要直接地在你的 propTypes 里声明 children 的类型应为一个函数。

```js
Mouse.propTypes = {
children: PropTypes.func.isRequired
};
```

## Caveats {#caveats}
## 注意事项 {#caveats}

### Be careful when using Render Props with React.PureComponent {#be-careful-when-using-render-props-with-reactpurecomponent}
### 将 Render Props 与 React.PureComponent 一起使用时要小心 {#be-careful-when-using-render-props-with-reactpurecomponent}

Using a render prop can negate the advantage that comes from using [`React.PureComponent`](/docs/react-api.html#reactpurecomponent) if you create the function inside a `render` method. This is because the shallow prop comparison will always return `false` for new props, and each `render` in this case will generate a new value for the render prop.
如果你在 render 方法里创建函数，那么使用 render prop 会抵消使用 [`React.PureComponent`](/docs/react-api.html#reactpurecomponent) 带来的优势。因为浅比较 props 的时候总会得到 false，并且在这种情况下每一个 `render` 对于 render prop 将会生成一个新的值。

For example, continuing with our `<Mouse>` component from above, if `Mouse` were to extend `React.PureComponent` instead of `React.Component`, our example would look like this:
例如，继续我们之前使用的 `<Mouse>` 组件，如果 `Mouse` 继承自 `React.PureComponent` 而不是 `React.Component`，我们的例子看起来就像这样：

```js
class Mouse extends React.PureComponent {
// Same implementation as above...
// 与上面相同的代码......
}

class MouseTracker extends React.Component {
Expand All @@ -287,8 +286,8 @@ class MouseTracker extends React.Component {
<h1>Move the mouse around!</h1>

{/*
This is bad! The value of the `render` prop will
be different on each render.
这是不好的！
每个渲染的 `render` prop的值将会是不同的。
*/}
<Mouse render={mouse => (
<Cat mouse={mouse} />
Expand All @@ -299,14 +298,14 @@ class MouseTracker extends React.Component {
}
```

In this example, each time `<MouseTracker>` renders, it generates a new function as the value of the `<Mouse render>` prop, thus negating the effect of `<Mouse>` extending `React.PureComponent` in the first place!
在这样例子中，每次 `<MouseTracker>` 渲染，它会生成一个新的函数作为 `<Mouse render>` 的 prop，因而在同时也抵消了继承自 `React.PureComponent` 的 `<Mouse>` 组件的效果！

To get around this problem, you can sometimes define the prop as an instance method, like so:
为了绕过这一问题，有时你可以定义一个 prop 作为实例方法，类似这样：

```js
class MouseTracker extends React.Component {
// Defined as an instance method, `this.renderTheCat` always
// refers to *same* function when we use it in render
// 定义为实例方法，`this.renderTheCat`始终
  // 当我们在渲染中使用它时，它指的是相同的函数
renderTheCat(mouse) {
return <Cat mouse={mouse} />;
}
Expand All @@ -322,4 +321,4 @@ class MouseTracker extends React.Component {
}
```

In cases where you cannot define the prop statically (e.g. because you need to close over the component's props and/or state) `<Mouse>` should extend `React.Component` instead.
如果你无法静态定义 prop（例如，因为你需要关闭组件的 props 和/或 state），则 `<Mouse>` 应该扩展 `React.Component`。

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