异步状态处理 - 元素码农

发布时间: 2025-03-23 08:25

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# 异步状态处理

本文将详细介绍React Native中异步状态管理的最佳实践和常见模式。通过实际案例,你将学会如何优雅地处理异步操作,提升应用的用户体验。

## 异步状态基础

### 1. 异步状态的组成

一个完整的异步状态通常包含以下几个部分：

```javascript
const [data, setData] = useState(null);      // 数据
const [loading, setLoading] = useState(false); // 加载状态
const [error, setError] = useState(null);     // 错误信息
```

### 2. 基本异步流程

```javascript
const fetchData = async () => {
  setLoading(true);
  setError(null);
  try {
    const response = await fetch('https://api.example.com/data');
    const result = await response.json();
    setData(result);
  } catch (err) {
    setError(err.message);
  } finally {
    setLoading(false);
  }
};
```

## 自定义Hook封装

### 1. useAsync Hook

```javascript
const useAsync = (asyncFunction, immediate = true) => {
  const [status, setStatus] = useState('idle');
  const [data, setData] = useState(null);
  const [error, setError] = useState(null);

const execute = useCallback(async () => {
    setStatus('pending');
    setData(null);
    setError(null);

try {
      const response = await asyncFunction();
      setData(response);
      setStatus('success');
      return response;
    } catch (err) {
      setError(err);
      setStatus('error');
      throw err;
    }
  }, [asyncFunction]);

useEffect(() => {
    if (immediate) {
      execute();
    }
  }, [execute, immediate]);

return { execute, status, data, error };
};
```

### 2. useFetch Hook

```javascript
const useFetch = (url, options = {}) => {
  const [state, setState] = useState({
    data: null,
    loading: true,
    error: null,
  });

useEffect(() => {
    const abortController = new AbortController();
    const signal = abortController.signal;

const fetchData = async () => {
      setState(prev => ({ ...prev, loading: true }));

try {
        const response = await fetch(url, {
          ...options,
          signal,
        });
        const data = await response.json();

setState({
          data,
          loading: false,
          error: null,
        });
      } catch (error) {
        if (error.name === 'AbortError') {
          return;
        }

setState({
          data: null,
          loading: false,
          error: error.message,
        });
      }
    };

fetchData();

return () => {
      abortController.abort();
    };
  }, [url, options]);

return state;
};
```

## 常见模式

### 1. 轮询模式

```javascript
const usePolling = (url, interval = 5000) => {
  const [data, setData] = useState(null);
  const [error, setError] = useState(null);

useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch(url);
        const result = await response.json();
        setData(result);
        setError(null);
      } catch (err) {
        setError(err.message);
      }
    };

fetchData(); // 初始加载
    const timer = setInterval(fetchData, interval);

return () => clearInterval(timer);
  }, [url, interval]);

return { data, error };
};
```

### 2. 重试机制

```javascript
const useRetry = (asyncFn, retryCount = 3, retryDelay = 1000) => {
  const [state, setState] = useState({
    data: null,
    loading: false,
    error: null,
    attempts: 0,
  });

const execute = useCallback(async () => {
    setState(prev => ({ ...prev, loading: true }));
    let attempts = 0;

while (attempts < retryCount) {
      try {
        const data = await asyncFn();
        setState({
          data,
          loading: false,
          error: null,
          attempts,
        });
        return data;
      } catch (error) {
        attempts++;
        if (attempts === retryCount) {
          setState({
            data: null,
            loading: false,
            error: error.message,
            attempts,
          });
          throw error;
        }
        await new Promise(resolve => setTimeout(resolve, retryDelay));
      }
    }
  }, [asyncFn, retryCount, retryDelay]);

return { ...state, execute };
};
```

### 3. 缓存管理

```javascript
const useCache = (key, fetcher, options = {}) => {
  const { ttl = 5 * 60 * 1000 } = options; // 默认5分钟缓存
  const cache = useRef(new Map());

const getCachedData = useCallback(() => {
    const cached = cache.current.get(key);
    if (!cached) return null;

const isExpired = Date.now() - cached.timestamp > ttl;
    if (isExpired) {
      cache.current.delete(key);
      return null;
    }

return cached.data;
  }, [key, ttl]);

const [state, setState] = useState({
    data: getCachedData(),
    loading: false,
    error: null,
  });

const fetchData = useCallback(async () => {
    setState(prev => ({ ...prev, loading: true }));

try {
      const data = await fetcher();
      cache.current.set(key, {
        data,
        timestamp: Date.now(),
      });
      setState({
        data,
        loading: false,
        error: null,
      });
    } catch (error) {
      setState({
        data: null,
        loading: false,
        error: error.message,
      });
    }
  }, [key, fetcher]);

useEffect(() => {
    if (!getCachedData()) {
      fetchData();
    }
  }, [getCachedData, fetchData]);

return { ...state, refresh: fetchData };
};
```

## 错误处理

### 1. 全局错误处理

```javascript
const ErrorBoundary = ({ children }) => {
  const [error, setError] = useState(null);

if (error) {
    return (
      <View style={styles.errorContainer}>
        <Text style={styles.errorText}>出错了: {error.message}</Text>
        <Button
          title="重试"
          onPress={() => setError(null)}
        />
      </View>
    );
  }

return (
    <View>
      {children}
    </View>
  );
};
```

### 2. 错误重试

```javascript
const RetryableErrorBoundary = ({ children, fallback }) => {
  const [error, setError] = useState(null);
  const [retryCount, setRetryCount] = useState(0);

const handleRetry = () => {
    setError(null);
    setRetryCount(count => count + 1);
  };

if (error) {
    return fallback({ error, retry: handleRetry, retryCount });
  }

return children;
};
```

## 性能优化

### 1. 防抖与节流

```javascript
const useDebounce = (value, delay) => {
  const [debouncedValue, setDebouncedValue] = useState(value);

useEffect(() => {
    const timer = setTimeout(() => {
      setDebouncedValue(value);
    }, delay);

return () => clearTimeout(timer);
  }, [value, delay]);

return debouncedValue;
};

const useThrottle = (value, delay) => {
  const [throttledValue, setThrottledValue] = useState(value);
  const lastExecuted = useRef(Date.now());

useEffect(() => {
    const handler = setTimeout(() => {
      if (Date.now() - lastExecuted.current >= delay) {
        setThrottledValue(value);
        lastExecuted.current = Date.now();
      }
    }, delay);

return () => clearTimeout(handler);
  }, [value, delay]);

return throttledValue;
};
```

### 2. 并发控制

```javascript
const useConcurrentRequests = (requests, concurrency = 3) => {
  const [results, setResults] = useState([]);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(null);

return { results, loading, error, execute: executeRequests };
};
```

## 最佳实践

1. 状态初始化
   - 为异步状态提供合理的初始值
   - 考虑加载状态和错误状态的默认值

2. 错误处理
   - 实现全局错误处理机制
   - 提供友好的错误提示
   - 添加重试机制

3. 性能优化
   - 使用缓存减少请求
   - 实现请求取消
   - 控制并发数量

4. 用户体验
   - 显示加载状态
   - 提供错误反馈
   - 支持刷新操作

## 参考资源

- [React Hooks文档](https://reactjs.org/docs/hooks-reference.html)
- [React Native网络请求](https://reactnative.dev/docs/network)
- [JavaScript异步编程](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises)

## 总结

通过本文的学习,你应该已经掌握了:

1. 异步状态管理的基本概念
2. 常用的异步状态处理模式
3. 自定义Hook的实现方法
4. 错误处理和性能优化技巧
5. 异步状态管理的最佳实践

在实际开发中,良好的异步状态管理对于提升应用性能和用户体验至关重要。建议根据具体场景选择合适的模式,并注意遵循最佳实践。