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

Included in Expo Go

GitHub

npm

更新日志

Recommended version:

~57.0.4

expo-font 允许从网页加载字体，并在 React Native 组件中使用它们。更多详细的用法信息请参见字体指南。

安装

Terminal

- npx expo install expo-font

- yarn expo install expo-font

- pnpm expo install expo-font

- bun expo install expo-font

If you are installing this in an existing React Native app, make sure to install expo in your project.

应用配置中的配置

有两种方式可以将字体添加到你的应用中：使用 expo-font 配置插件（推荐用于 Android 和 iOS）或在运行时加载它们（这在包括 web 在内的所有平台上都可用）。

在 Android 和 iOS 上，该插件允许你在构建时嵌入字体文件，这比 useFonts 或 loadAsync 更高效。设置好配置插件并运行 prebuild 后，你就可以立即渲染自定义字体。该插件可以通过不同方式进行配置，参见字体指南了解如何使用它。

Example app.json with config plugin

app.json

{
  "expo": {
    "plugins": [
      [
        "expo-font",
        {
          "fonts": ["./path/to/file.ttf"],
          "android": {
            "fonts": [
              {
                "fontFamily": "Source Serif 4",
                "fontDefinitions": [
                  {
                    "path": "./path/to/SourceSerif4-ExtraBold.ttf",
                    "weight": 800
                  }
                ]
              }
            ]
          },
          "ios": {
            "fonts": ["./path/to/SourceSerif4-ExtraBold.ttf"]
          }
        }
      ]
    ]
  }
}

Configurable properties

Name	Default	Description
`fonts`	`[]`	一个要链接到原生项目的字体定义数组。路径应相对于项目根目录。在 Android 上，文件名会成为字体族名称。在 iOS 上，字体族名称始终直接取自字体文件，并且可能与文件名不同——请遵循命名建议，或使用 `getLoadedFonts` 查看可用的字体。
`android`	`{}`	一个包含 `fonts` 字体定义数组的对象，用于将字体链接到 Android 上的原生项目。在 `fonts` 中使用对象语法，以嵌入带有自定义字体族名称的 xml 字体。
`ios`	`{}`	一个包含 `fonts` 字体文件路径数组的对象，用于将字体链接到 iOS 上的原生项目。字体族名称直接取自字体文件。

Are you using this library in an existing React Native app?

Android: 将字体文件复制到 android/app/src/main/assets/fonts。
iOS: 请参阅 Apple Developer 文档中的将自定义字体添加到你的应用。

用法

如果你不想使用配置插件，你可以在运行时使用 useFonts Hook 加载字体，如下所示：

加载并使用自定义字体的示例

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() {
  // 只有在不能使用配置插件时才使用 `useFonts`。
  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 }}>平台默认字体</Text>
    </View>
  );
}

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

API

import * as Font from 'expo-font';

Constants

`useFonts`

Android

iOS

tvOS

Web

Type: UseFontHook

Load a map of fonts at runtime with loadAsync. This returns true 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.

Example

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

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.

`renderToImageAsync(glyphs, options)`

Android

iOS

Parameter	Type	Description
glyphs	`string`	Text to be exported.
options(optional)	`RenderToImageOptions`	RenderToImageOptions.

Creates an image with provided text.

Returns:

Promise<RenderToImageResult>

Promise which fulfils with image metadata.

Interfaces

`RenderToImageOptions`

Android

iOS

tvOS

Web

Property	Type	Description
color(optional)	`string`	Font color Default:`'black'`
fontFamily(optional)	`string`	Font family name. Default:`system default`
lineHeight(optional)	`number`	Line height of the text. Accepts number in dp units.
size(optional)	`number`	Size of the font. Default:`24`

`RenderToImageResult`

Android

iOS

tvOS

Web

Property	Type	Description
height	`number`	Image height in dp.
scale	`number`	Scale factor of the image. Multiply the dp dimensions by this value to get the dimensions in pixels.
uri	`string`	The file uri to the image.
width	`number`	Image width in dp.

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.
testString(optional)	`string`	Only for: Web Sets a custom test string passed to the FontFace Observer.
uri(optional)	`string \| number`	-

`FontSource`

Android

iOS

tvOS

Web

Literal type: union

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

`ServerFontResourceDescriptor`

Android

iOS

tvOS

Web

Type: object shaped as below:

Property	Type	Description
css	`string`	-
id	`string`	-
type	`'style'`	-

Or object shaped as below:

Property	Type	Description
as	`'font'`	-
crossOrigin(optional)	`'anonymous' \| 'use-credentials' \| undefined`	-
href	`string`	-
rel	`'preload'`	-
type	`'link'`	-

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

代码	描述
ERR_FONT_API	如果传递给 `loadAsync` 的参数无效。
ERR_FONT_SOURCE	所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。
ERR_DOWNLOAD	无法下载所提供的资源。
ERR_FONT_FAMILY	提供的字体族名称无效。
ERR_UNLOAD	尝试卸载尚未完成加载的字体。