native-data-fetching

在实现或调试任何网络请求、API 调用或数据获取时使用。涵盖 fetch API、React Query、SWR、错误处理、缓存、离线支持和 Expo Router 数据加载器 (useLoaderData)。

## 概述（中文）

在实现或调试任何网络请求、API 调用或数据获取时使用。涵盖 fetch API、React Query、SWR、错误处理、缓存、离线支持和 Expo Router 数据加载器 (useLoaderData)。

## 原文

# Expo Networking

**You MUST use this skill for ANY networking work including API requests, data fetching, caching, or network debugging.**

## References

Consult these resources as needed:

```
references/
  expo-router-loaders.md   Route-level data loading with Expo Router loaders (web, SDK 55+)
```

## When to Use

Use this skill when:

- Implementing API requests
- Setting up data fetching (React Query, SWR)
- Using Expo Router data loaders (`useLoaderData`, web SDK 55+)
- Debugging network failures
- Implementing caching strategies
- Handling offline scenarios
- Authentication/token management
- Configuring API URLs and environment variables

## Preferences

- Avoid axios, prefer expo/fetch

## Common Issues & Solutions

### 1. Basic Fetch Usage

**Simple GET request**:

```tsx
const fetchUser = async (userId: string) => {
  const response = await fetch(`https://api.example.com/users/${userId}`);

  if (!response.ok) {
    throw new Error(`HTTP error! status: ${response.status}`);
  }

  return response.json();
};
```

**POST request with body**:

```tsx
const createUser = async (userData: UserData) => {
  const response = await fetch("https://api.example.com/users", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${token}`,
    },
    body: JSON.stringify(userData),
  });

  if (!response.ok) {
    const error = await response.json();
    throw new Error(error.message);
  }

  return response.json();
};
```

---

### 2. React Query (TanStack Query)

**Setup**:

```tsx
// app/_layout.tsx
import { QueryClient, QueryClientProvider } from "@tanstack/react-query";

const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 1000 * 60 * 5, // 5 minutes
      retry: 2,
    },
  },
});

export default function RootLayout() {
  return (
    <QueryClientProvider client={queryClient}>
      <Stack />
    </QueryClientProvider>
  );
}
```

**Fetching data**:

```tsx
import { useQuery } from "@tanstack/react-query";

function UserProfile({ userId }: { userId: string }) {
  const { data, isLoading, error, refetch } = useQuery({
    queryKey: ["user", userId],
    queryFn: () => fetchUser(userId),
  });

  if (isLoading) return <Loading />;
  if (error) return <Error message={error.message} />;

  return <Profile user={data} />;
}
```

**Mutations**:

```tsx
import { useMutation, useQueryClient } from "@tanstack/react-query";

function CreateUserForm() {
  const queryClient = useQueryClient();

  const mutation = useMutation({
    mutationFn: createUser,
    onSuccess: () => {
      // Invalidate and refetch
      queryClient.invalidateQueries({ queryKey: ["users"] });
    },
  });

  const handleSubmit = (data: UserData) => {
    mutation.mutate(data);
  };

  return <Form onSubmit={handleSubmit} isLoading={mutation.isPending} />;
}
```

---

### 3. Error Handling

**Comprehensive error handling**:

```tsx
class ApiError extends Error {
  constructor(message: string, public status: number, public code?: string) {
    super(message);
    this.name = "ApiError";
  }
}

const fetchWithErrorHandling = async (url: string, options?: RequestInit) => {
  try {
    const response = await fetch(url, options);

    if (!response.ok) {
      const error = await response.json().catch(() => ({}));
      throw new ApiError(
        error.message || "Request failed",
        response.status,
        error.code
      );
    }

    return response.json();
  } catch (error) {
    if (error instanceof ApiError) {
      throw error;
    }
    // Network error (no internet, timeout, etc.)
    throw new ApiError("Network error", 0, "NETWORK_ERROR");
  }
};
```

**Retry logic**:

```tsx
const fetchWithRetry = async (
  url: string,
  options?: RequestInit,
  retries = 3
) => {
  for (let i = 0; i < retries; i++) {
    try {
      return await fetchWithErrorHandling(url, options);
    } catch (error) {
      if (i === retries - 1) throw error;
      // Exponential backoff
      await new Promise((r) => setTimeout(r, Math.pow(2, i) * 1000));
    }
  }
};
```

---

### 4. Authentication

**Token management**:

```tsx
import * as SecureStore from "expo-secure-store";

const TOKEN_KEY = "auth_token";

export const auth = {
  getToken: () => SecureStore.getItemAsync(TOKEN_KEY),
  setToken: (token: string) => SecureStore.setItemAsync(TOKEN_KEY, token),
  removeToken: () => SecureStore.deleteItemAsync(TOKEN_KEY),
};

// Authenticated fetch wrapper
const authFetch = async (url: string, options: RequestInit = {}) => {
  const token = await auth.getToken();

  return fetch(url, {
    ...options,
    headers: {
      ...options.headers,
      Authorization: token ? `Bearer ${token}` : "",
    },
  });
};
```

**Token refresh**:

```tsx
let isRefreshing = false;
let refreshPromise: Promise<string> | null = null;

const getValidToken = async (): Promise<string> => {
  const token = await auth.getToken();

  if (!token || isTokenExpired(token)) {
    if (!isRefreshing) {
      isRefreshing = true;
      refreshPromise = refreshToken().finally(() => {
        isRefreshing = false;
        refreshPromise = null;
      });
    }
    return refreshPromise!;
  }

  return token;
};
```

---

### 5. Offline Support

**Check network status**:

```tsx
import NetInfo from "@react-native-community/netinfo";

// Hook for network status
function useNetworkStatus() {
  const [isOnline, setIsOnline] = useState(true);

  useEffect(() => {
    return NetInfo.addEventListener((state) => {
      setIsOnline(state.isConnected ?? true);
    });
  }, []);

  return isOnline;
}
```

**Offline-first with React Query**:

```tsx
import { onlineManager } from "@tanstack/react-query";
import NetInfo from "@react-native-community/netinfo";

// Sync React Query with network status
onlineManager.setEventListener((setOnline) => {
  return NetInfo.addEventListener((state) => {
    setOnline(state.isConnected ?? true);
  });
});

// Queries will pause when offline and resume when online
```

---

### 6. Environment Variables

**Using environment variables for API configuration**:

Expo supports environment variables with the `EXPO_PUBLIC_` prefix. These are inlined at build time and available in your JavaScript code.

```tsx
// .env
EXPO_PUBLIC_API_URL=https://api.example.com
EXPO_PUBLIC_API_VERSION=v1

// Usage in code
const API_URL = process.env.EXPO_PUBLIC_API_URL;

const fetchUsers = async () => {
  const response = await fetch(`${API_URL}/users`);
  return response.json();
};
```

**Environment-specific configuration**:

```tsx
// .env.development
EXPO_PUBLIC_API_URL=http://localhost:3000

// .env.production
EXPO_PUBLIC_API_URL=https://api.production.com
```

**Creating an API client with environment config**:

```tsx
// api/client.ts
const BASE_URL = process.env.EXPO_PUBLIC_API_URL;

if (!BASE_URL) {
  throw new Error("EXPO_PUBLIC_API_URL is not defined");
}

export const apiClient = {
  get: async <T,>(path: string): Promise<T> => {
    const response = await fetch(`${BASE_URL}${path}`);
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    return response.json();
  },

  post: async <T,>(path: string, body: unknown): Promise<T> => {
    const response = await fetch(`${BASE_URL}${path}`, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify(body),
    });
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    return response.json();
  },
};
```

**Important notes**:

- Only variables prefixed with `EXPO_PUBLIC_` are exposed to the client bundle
- Never put secrets (API keys with write access, database passwords) in `EXPO_PUBLIC_` variables—they're visible in the built app
- Environment variables are inlined at **build time**, not runtime
- Restart the dev server after changing `.env` files
- For server-side secrets in API rou