Great questions! Let's break them down one by one with practical details:

Absolutely—this is a best practice you shouldn't skip. While mobile operating systems might eventually reclaim unused resources, failing to close the database can lead to avoidable issues:

• Uncommitted transactions getting rolled back unexpectedly
• Resource leaks that hurt performance if the app is resumed later
• Rare but possible database corruption in edge cases

Manual closure ensures clean termination of connections and protects your data integrity.

App exit detection varies by platform (Android vs. iOS) due to their differing lifecycle behaviors. Here's how to handle both reliably:

For Android: #

• Hardware Back Button: Use the BackHandler API to listen for the back press event, especially when the user is on your app's root screen (a clear signal they intend to exit).
• Background State: Listen for the background state via AppState—Android apps often stay suspended in the background before being killed, so cleaning up here covers both explicit exits and system-initiated termination.

For iOS: #

• Background State: iOS doesn't have a direct "exit" event (users swipe up to close, but the system may have already suspended the app). Use AppState to listen for the background state—this is the last reliable hook before the app might be terminated.

Here's a combined code example to handle both platforms:

import { AppState, BackHandler, Platform, useEffect } from 'react-native';
// Assume `db` is your initialized SQLite database instance

const closeDatabase = async () => {
  try {
    await db.close();
    console.log('Database closed successfully');
  } catch (err) {
    console.error('Failed to close database:', err);
  }
};

const YourApp = () => {
  useEffect(() => {
    // Handle app state transitions to background
    const handleAppStateChange = (nextState) => {
      if (nextState === 'background') {
        closeDatabase();
      }
    };
    const appStateSub = AppState.addEventListener('change', handleAppStateChange);

    // Handle Android back button exit
    let backHandler;
    if (Platform.OS === 'android') {
      backHandler = BackHandler.addEventListener('hardwareBackPress', () => {
        // Replace with your logic to check if user is on the root screen
        const isRootScreen = true; 
        if (isRootScreen) {
          closeDatabase();
          return false; // Let the system handle the actual exit
        }
        return true; // Consume the back press for non-root screens
      });
    }

    // Clean up subscriptions when the component unmounts
    return () => {
      appStateSub.remove();
      backHandler?.remove();
    };
  }, []);

  // Rest of your app component code
  return /* ... */;
};

No, React Native doesn't auto-manage all resources. You'll need to manually clean up certain types to avoid memory leaks and performance degradation:

Resources requiring manual cleanup: #

• Native bridge resources: SQLite connections, file handles, camera/microphone access, Bluetooth connections, or any native module resources. JS garbage collection can't reach native-side resources, so you have to clean them explicitly.
• JS subscriptions & timers: Event listeners (e.g., AppState, DeviceEventEmitter), setTimeout/setInterval, Redux store subscriptions, or ongoing listeners. Always remove these when components unmount.
• Large in-memory objects: Big data sets (parsed JSON, image buffers) should have their references nullified when no longer needed to speed up garbage collection.

Resources that are auto-managed: #

• React component instances: React's reconciliation process automatically cleans up unmounted components.
• Cached assets: Images loaded via the Image component are cached and evicted by React Native's image loader when memory is low.
• Basic JS variables: Standard objects/primitives are handled by the garbage collector once no active references exist.

Key takeaway: #

Always clean up resources that bridge to native code or create ongoing asynchronous processes—this keeps your app stable and performant over time.

内容的提问来源于stack exchange，提问作者spin_eight