react-native - React Native - 观察 AsyncStorage 值的变化？

Question

有没有办法订阅 AsyncStorage值(value)变化？我在一个地方有一个设置保存在 AsyncStorage在应用程序中，这会影响其他所有屏幕。我需要观察该值，以便可以更新所有屏幕。我试过 getValue方法但它似乎最初只获取一个值，并且不会在更改时更新。

Answer 1

我通过构建一个同步到 AsyncStorage 的 React Context 在我的应用程序中解决了这个问题。
在你的情况下，你可以有一个项目，例如 appSettings .这将是一个字符串化的 JSON 对象，其中包含您的所有应用设置。

const AppSettingsContext = React.createContext({})

const AppSettingsContextProvider = ({children}) => {
  const [appSettingsInitialized, setAppSettingsInitialized] = useState(false)
  const [appSettings, setAppSettings] = useState({}) // could use some default values instead of empty object

  // On mount, get the current value of `appSettings` in AsyncStorage
  useEffect(() => {
    AsyncStorage
      .getItem('appSettings')
      .then(data => {
        // If data is returned, the storage item existed already and we set the appSettings state to that.
        if (data) {
          setAppSettings(JSON.parse(data))
        }
        // If data is null, the appSettings keeps the default value (in this case an empty object)/

        // We set appSettingsInitialized to true to signal that we have successfully retrieved the initial values.
        setAppSettingsInitialized(true)
      })
  }, [])

  // setSettings sets the local state and AsyncStorage
  const setSettings = (key, value) => {
    const mergedSettings = {
      ...appSettings,
      [key]: value
    }
    // First, merge the current state with the new value
    setAppSettings(mergedSettings)

    // Then update the AsyncStorage item
    AsyncStorage.setItem('appSettings', JSON.stringify(mergedSettings))
  }

  return (
    <AppSettingsContext.Provider value={{
      appSettings,
      appSettingsInitialized,
      setSettings,
    }}>
      {children}
    </AppSettingsContext.Provider>
  )
}

(请注意，这是一个非常基本的版本，没有错误处理)
然后将您的应用程序包装在 AppSettingsContextProvider 中

const App = () => (
  <AppSettingsContextProvider>
    {/* Other components */}
  </AppSettingsContextProvider>
)

然后使用来自任何子组件的上下文:

const SomeChildComponent = () => {
  const { appSettingsInitialized, appSettings } = useContext(AppSettingsContext)

  // For example: wait until initial appSettings have been retrieved AsyncStorage,
  // then use some value that you expect to be present in your business logic.
  // In this case, setAppTheme would set the them color for the whole app, using a
  // `theme` setting saved by the user.
  useEffect(() => {
    if (appSettingsInitialized) {
      setAppTheme(appSettings.theme)
    }
  }, [appSettingsInitialized])

  // Update settings like this for example
  const updateThemeSetting = (newThemeValue) => {
    setSettings('theme', newThemeValue) // eg 'dark', 'light', etc
  }
}