Expo 字体

一个允许在运行时加载字体并在 React Native 组件中使用它们的库。

Android

iOS

tvOS

Web

expo-font 允许从网络加载字体并在 React Native 组件中使用它们。请参阅字体指南中更详细的使用信息。

¥expo-font allows loading fonts from the web and using them in React Native components. See more detailed usage information in the Fonts guide.

安装

¥Installation

Terminal

- npx expo install expo-font

If you are installing this in an existing React Native app, start by installing expo in your project. Then, follow the additional instructions as mentioned by the library's README under "Installation in bare React Native projects" section.

应用配置中的配置

¥Configuration in app config

如果你在项目中使用配置插件（EAS 构建或 npx expo run: [android|ios]），则推荐通过 expo-font 内置配置插件向你的应用添加字体。该插件允许你在构建时嵌入字体文件，这比使用 loadAsync 更有效率。查看字体指南以了解如何使用它。

¥The recommended way to add fonts to your app is through expo-font built-in config plugin if you use config plugins in your project (EAS Build or npx expo run: [android|ios]). The plugin allows you to embed font files at build time which is more efficient than using loadAsync. See the Fonts guide on how to use it.

Example app.json with config plugin

app.json

{
"expo": {
  "plugins": [
    [
      "expo-font",
      {
        "fonts": ["path/to/file.ttf"]
      }
    ]
  ]
}
}

Configurable properties

Name	Default	Description
`fonts`	`[]`	An array of font files to link to the native project. The paths should be relative to the project root. The file names will become the font family names on Android. On iOS, the font family name may not be the same as the file name — use `getLoadedFonts` to see what fonts are available.

Are you using this library in a bare React Native app?

安卓：将字体文件复制到 android/app/src/main/assets/fonts。

¥Android: Copy font files to android/app/src/main/assets/fonts.
iOS：请参阅 Apple 开发者文档中的向你的应用添加自定义字体。

¥iOS: See Adding a Custom Font to Your App in the Apple Developer documentation.

用法

¥Usage

Minimal example of using a custom font

import { useFonts } from 'expo-font';
import * as SplashScreen from 'expo-splash-screen';
import { useEffect } from 'react';
import { Text, View, StyleSheet } from 'react-native';

SplashScreen.preventAutoHideAsync();

export default function App() {
const [loaded, error] = useFonts({
  'Inter-Black': require('./assets/fonts/Inter-Black.otf'),
});

useEffect(() => {
  if (loaded || error) {
    SplashScreen.hideAsync();
  }
}, [loaded, error]);

if (!loaded && !error) {
  return null;
}

return (
  <View style={styles.container}>
    <Text style={{ fontFamily: 'Inter-Black', fontSize: 30 }}>Inter Black</Text>
    <Text style={{ fontSize: 30 }}>Platform Default</Text>
  </View>
);
}

const styles = StyleSheet.create({
container: {
  flex: 1,
  justifyContent: 'center',
  alignItems: 'center',
},
});

API

import * as Font from 'expo-font';

Hooks

`useFonts(map)`

Android

iOS

tvOS

Web

Parameter	Type	Description
map	`string \| Record<string, FontSource>`	A map of `fontFamily`s to `FontSource`s. After loading the font you can use the key in the `fontFamily` style prop of a `Text` element.

Load a map of fonts with loadAsync. This returns a boolean if the fonts are loaded and ready to use. It also returns an error if something went wrong, to use in development.

Note, the fonts are not "reloaded" when you dynamically change the font map.

Returns:

[boolean, null | Error]

loaded (boolean) - A boolean to detect if the font for fontFamily has finished loading.
error (Error | null) - An error encountered when loading the fonts.

Example

const [loaded, error] = useFonts({ ... });

Methods

`getLoadedFonts()`

Android

iOS

tvOS

Web

Synchronously get all the fonts that have been loaded. This includes fonts that were bundled at build time using the config plugin, as well as those loaded at runtime using loadAsync.

Returns:

string[]

Returns array of strings which you can use as fontFamily style prop.

`isLoaded(fontFamily)`

Android

iOS

tvOS

Web

Parameter	Type	Description
fontFamily	`string`	The name used to load the `FontResource`.

Synchronously detect if the font for fontFamily has finished loading.

Returns:

boolean

Returns true if the font has fully loaded.

`isLoading(fontFamily)`

Android

iOS

tvOS

Web

Parameter	Type	Description
fontFamily	`string`	The name used to load the `FontResource`.

Synchronously detect if the font for fontFamily is still being loaded.

Returns:

boolean

Returns true if the font is still loading.

`loadAsync(fontFamilyOrFontMap, source)`

Android

iOS

tvOS

Web

Parameter	Type	Description
fontFamilyOrFontMap	`string \| Record<string, FontSource>`	String or map of values that can be used as the `fontFamily` style prop with React Native `Text` elements.
source(optional)	`FontSource`	The font asset that should be loaded into the `fontFamily` namespace.

An efficient method for loading fonts from static or remote resources which can then be used with the platform's native text elements. In the browser, this generates a @font-face block in a shared style sheet for fonts. No CSS is needed to use this method.

Note: We recommend using the config plugin instead whenever possible.

Returns:

Promise<void>

Returns a promise that fulfils when the font has loaded. Often you may want to wrap the method in a try/catch/finally to ensure the app continues if the font fails to load.

Types

`FontResource`

Android

iOS

tvOS

Web

An object used to dictate the resource that is loaded into the provided font namespace when used with loadAsync.

Property	Type	Description
default(optional)	`string`	-
display(optional)	`FontDisplay`	Only for: Web Sets the `font-display` property for a given typeface in the browser.
uri(optional)	`string \| number`	-

`FontSource`

Android

iOS

tvOS

Web

Literal Type: multiple types

The different types of assets you can provide to the loadAsync() function. A font source can be a URI, a module ID, or an Expo Asset.

Acceptable values are: string | number | Asset | FontResource

Enums

`FontDisplay`

Web

Sets the font-display for a given typeface. The default font value on web is FontDisplay.AUTO. Even though setting the fontDisplay does nothing on native platforms, the default behavior emulates FontDisplay.SWAP on flagship devices like iOS, Samsung, Pixel, etc. Default functionality varies on One Plus devices. In the browser this value is set in the generated @font-face CSS block and not as a style property meaning you cannot dynamically change this value based on the element it's used in.

`AUTO`

FontDisplay.AUTO ＝ "auto"

(Default) The font display strategy is defined by the user agent or platform. This generally defaults to the text being invisible until the font is loaded. Good for buttons or banners that require a specific treatment.

`BLOCK`

FontDisplay.BLOCK ＝ "block"

The text will be invisible until the font has loaded. If the font fails to load then nothing will appear - it's best to turn this off when debugging missing text.

`FALLBACK`

FontDisplay.FALLBACK ＝ "fallback"

Splits the behavior between SWAP and BLOCK. There will be a 100ms timeout where the text with a custom font is invisible, after that the text will either swap to the styled text or it'll show the unstyled text and continue to load the custom font. This is good for buttons that need a custom font but should also be quickly available to screen-readers.

`OPTIONAL`

FontDisplay.OPTIONAL ＝ "optional"

This works almost identically to FALLBACK, the only difference is that the browser will decide to load the font based on slow connection speed or critical resource demand.

`SWAP`

FontDisplay.SWAP ＝ "swap"

Fallback text is rendered immediately with a default font while the desired font is loaded. This is good for making the content appear to load instantly and is usually preferred.

错误代码

¥Error codes

代码	描述
ERR_FONT_API	如果传递给 `loadAsync` 的参数无效。
ERR_FONT_SOURCE	提供的资源类型不正确。
ERR_WEB_ENVIRONMENT	浏览器的 `document` 元素不支持注入字体。
错误 _ 下载	无法下载提供的资源。
ERR_FONT_FAMILY	提供的字体系列名称无效。
错误 _ 卸载	尝试卸载尚未完成加载的字体。