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请求权限并获取推送令牌

使用 expo-notifications 请求通知权限，获取 Expo 推送令牌，并将令牌发送到后端服务器保存。

请求权限并获取推送令牌 是 CoddyKit 上的免费 React Native Academy 课时。 这是第 1 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 React Native Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 React Native Academy 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

What Are Push Notifications?

Push notifications are messages sent from your server to a user's device even when the app is closed. They appear in the device's notification center, show on the lock screen, and can trigger a badge count on the app icon. On mobile they are one of the most powerful re-engagement tools available.

The flow for push notifications involves three parties: your app (registers the device), your server (decides when to send), and a push gateway (Apple APNs for iOS, Google FCM for Android). Expo wraps both gateways with a unified push service.

Installing expo-notifications

The expo-notifications package provides a unified API for push notifications on both iOS and Android. Install it with the Expo CLI, which handles installing the correct native version for your Expo SDK.

Push notifications require a development build (not Expo Go) because they need APNs entitlements embedded in the iOS app binary. Android push works in Expo Go but iOS does not. For production, EAS Build handles the certificate configuration automatically.

// Install:
// npx expo install expo-notifications

// In app.json, configure notification appearance:
{
  'expo': {
    'notification': {
      'icon': './assets/notification-icon.png',
      'color': '#ffffff',
      'androidMode': 'default',
      'androidCollapsedTitle': '#{unread_notifications} new updates'
    }
  }
}

Requesting Notification Permission

Before sending or receiving notifications, you must request permission from the user. On iOS this shows the system permission dialog the first time. On Android 13+ (API 33+) you must also explicitly request permission; on older Android versions it's granted automatically.

Use Notifications.requestPermissionsAsync() and check the returned status. The status is 'granted', 'denied', or 'undetermined'. If denied, the user must manually re-enable in Settings — you cannot show the dialog again.

import * as Notifications from 'expo-notifications';

async function requestPushPermission() {
  const { status: existingStatus } = await Notifications.getPermissionsAsync();

  let finalStatus = existingStatus;
  if (existingStatus !== 'granted') {
    const { status } = await Notifications.requestPermissionsAsync();
    finalStatus = status;
  }

  if (finalStatus !== 'granted') {
    console.log('Push permission denied');
    return false;
  }
  return true;
}

Getting the Expo Push Token

An Expo Push Token is a unique identifier for the app+device+user combination. It looks like ExponentPushToken[xxxxxxxxxxxxxxxxxxxxxx]. You pass this token to your server so it can send notifications to this specific device later.

Use Notifications.getExpoPushTokenAsync() to retrieve the token. This must be called after permission is granted. For production (non-Expo) builds you also need to provide the projectId from your Expo project.

import * as Notifications from 'expo-notifications';
import Constants from 'expo-constants';

async function getExpoPushToken() {
  const token = await Notifications.getExpoPushTokenAsync({
    projectId: Constants.expoConfig.extra.eas.projectId,
  });
  console.log('Push token:', token.data);
  // 'ExponentPushToken[AbCdEfGhIjKl...]'
  return token.data;
}

Storing the Token on Your Server

The push token is only useful if your server has it. After retrieving the token, send it to your backend via an API call and store it associated with the user account. A user might use multiple devices — store one token per device per user.

Tokens can change — when a user reinstalls the app or resets their device. Build your server to handle token updates: either overwrite the old token for the same user, or store multiple tokens per user and handle invalid token responses from the push gateway by removing stale tokens.

async function registerForPushNotifications(userId) {
  const hasPermission = await requestPushPermission();
  if (!hasPermission) return;

  const token = await getExpoPushToken();

  // Send to your backend:
  await fetch('https://api.myapp.com/users/' + userId + '/push-token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ token }),
  });
}

Calling Registration at the Right Time

Call the registration function at an appropriate moment in the user journey — typically right after the user logs in or completes onboarding. Requesting push permission too early (on app first launch) before the user understands the app's value reduces acceptance rates.

Use a useEffect in your authenticated root component to trigger registration once when the user is authenticated. Persist the registration status in AsyncStorage to avoid requesting permission on every launch.

import { useEffect } from 'react';
import AsyncStorage from '@react-native-async-storage/async-storage';

function usePostLoginPushRegistration(userId) {
  useEffect(() => {
    if (!userId) return;

    AsyncStorage.getItem('pushRegistered').then((registered) => {
      if (!registered) {
        registerForPushNotifications(userId).then(() => {
          AsyncStorage.setItem('pushRegistered', 'true');
        });
      }
    });
  }, [userId]);
}

Android-Specific: Notification Channels

Android 8+ requires notification channels — logical groupings that give users fine-grained control over which types of notifications they receive. Create channels with Notifications.setNotificationChannelAsync() before sending any notifications. On iOS this is not needed.

Use descriptive channel IDs and names that mean something to users in the Settings notification page. For example, messages, promotions, and system. Assign appropriate importance levels — HIGH for urgent notifications, DEFAULT for standard ones.

import * as Notifications from 'expo-notifications';
import { Platform } from 'react-native';

async function setupNotificationChannels() {
  if (Platform.OS === 'android') {
    await Notifications.setNotificationChannelAsync('messages', {
      name: 'Messages',
      importance: Notifications.AndroidImportance.HIGH,
      vibrationPattern: [0, 250, 250, 250],
      lightColor: '#FF231F7C',
    });

    await Notifications.setNotificationChannelAsync('promotions', {
      name: 'Promotions',
      importance: Notifications.AndroidImportance.DEFAULT,
    });
  }
}

Configuring Notification Presentation

By default, expo-notifications does not show notifications when the app is in the foreground. Configure the default notification handler with Notifications.setNotificationHandler to control this behavior. Set at the top level of your app, before any components mount.

The handler function receives each notification and returns a config object specifying whether to play a sound, show an alert, and set the badge count. Set up this handler once in your app entry file (App.js or index.js).

import * as Notifications from 'expo-notifications';

// At app root level (outside components):
Notifications.setNotificationHandler({
  handleNotification: async () => ({
    shouldShowAlert: true,
    shouldPlaySound: true,
    shouldSetBadge: true,
  }),
});

export default function App() {
  return <NavigationContainer>...</NavigationContainer>;
}

Getting a Native Device Token

For production apps not using Expo's push service (e.g., integrating directly with APNs or FCM), use Notifications.getDevicePushTokenAsync() instead of the Expo push token. This returns the raw APNs or FCM device token that you can pass directly to those services.

The native token is a hexadecimal string (iOS) or registration token (Android). Handle both cases on your server. When using native tokens you must also handle the certificate/key setup for APNs and the google-services.json for FCM separately.

// For direct APNs/FCM integration (not Expo push service):
const nativeToken = await Notifications.getDevicePushTokenAsync();
console.log('Native token type:', nativeToken.type); // 'ios' or 'android'
console.log('Native token data:', nativeToken.data); // raw APNs/FCM token

// Send to your server for direct gateway integration:

Handling Token Refresh

Push tokens can be invalidated and refreshed by the OS — for example when the user restores from a backup, reinstalls the app, or resets their device. Listen for token changes with Notifications.addPushTokenListener and update your server with the new token when this fires.

A robust push notification system always handles token refresh. Unregistered tokens cause silent delivery failures on your server. Clean up stale tokens from your database when the push gateway returns a DeviceNotRegistered error.

useEffect(() => {
  const tokenSubscription = Notifications.addPushTokenListener(
    async ({ data: newToken }) => {
      console.log('Push token refreshed:', newToken);
      // Update server with new token
      await fetch('/api/push-token/refresh', {
        method: 'PUT',
        body: JSON.stringify({ token: newToken }),
      });
    }
  );

  return () => tokenSubscription.remove();
}, []);

Privacy and Best Practices

Push token management best practices:

  • Never log tokens in production — they are credentials that identify specific devices.
  • Encrypt tokens at rest on your server — a leaked token database can enable notification spam.
  • Associate tokens with users — delete tokens when users delete their account or opt out of notifications.
  • Batch token updates — don't call the server on every app launch, only when the token changes or at first registration.
  • Respect user preferences — provide in-app notification settings and honor them on your server.

Quick Check

Test your understanding of React Native Mobile Development concepts from this lesson.

Lesson Recap

In this lesson you learned: Notifications.requestPermissionsAsync() requests OS permission and must be granted before getting a push token, Notifications.getExpoPushTokenAsync() returns a token like ExponentPushToken[...] that identifies the device to your backend, and tokens must be stored on your server and updated when they change to maintain reliable delivery. Next up we send push notifications to devices using the Expo Push API from a server.

常见问题解答

「请求权限并获取推送令牌」课时是免费的吗？

是的 — 「请求权限并获取推送令牌」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 React Native Academy 课程的其余内容，请升级到 CoddyKit PRO。 React Native Academy 课程共包含 4 节课。

「请求权限并获取推送令牌」这节课中我会学到什么？

使用 expo-notifications 请求通知权限，获取 Expo 推送令牌，并将令牌发送到后端服务器保存。 你通过在浏览器中直接运行的动手代码来练习 React Native Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 React Native Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 React Native Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 1 节课，共 4 节。

「请求权限并获取推送令牌」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 React Native Academy 课中编写并运行代码吗？

能。每节 React Native Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

此课程中的所有课时

  1. 请求权限并获取推送令牌
  2. 通过 Expo Push API 发送通知
  3. 处理前台与后台通知
  4. 通知渠道与丰富内容
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