React Native

Unlike React running inside the browsers, React Native has a very different user experience. For example there is no “tab focus”, switching from the background to the app is considered as a “focus” instead. To customize these behaviors, you can replace the default browser focus and online events listeners with React Native’s app state detection and other native ported API, and configure SWR to use them.

Example

Global Setup

You can wrap your app under SWRConfig and preconfig all configurations there

<SWRConfig
  value={{
    // ...
  }}
>
  <App>
</SWRConfig>

Customize focus and reconnect Events

There’re few configurations you need to take care of such as isOnline, isVisible, initFocus and initReconnect.

isOnline and isVisible are functions that return a boolean, to determine if the application is “active”. By default, SWR will bail out a revalidation if these conditions are not met.

When using initFocus and initReconnect, it’s required to also set up a custom cache provider. You can use an empty Map() or any storage you prefer.

<SWRConfig
  value={{
    provider: () => new Map(),
    isOnline() {
      /* Customize the network state detector */
      return true
    },
    isVisible() {
      /* Customize the visibility state detector */
      return true
    },
    initFocus(callback) {
      /* Register the listener with your state provider */
    },
    initReconnect(callback) {
      /* Register the listener with your state provider */
    }
  }}
>
  <App />
</SWRConfig>

Let’s take initFocus as example:

import { AppState } from 'react-native'
 
// ...
 
<SWRConfig
  value={{
    provider: () => new Map(),
    isVisible: () => { return true },
    initFocus(callback) {
      let appState = AppState.currentState
 
      const onAppStateChange = (nextAppState) => {
        /* If it's resuming from background or inactive mode to active one */
        if (appState.match(/inactive|background/) && nextAppState === 'active') {
          callback()
        }
        appState = nextAppState
      }
 
      // Subscribe to the app state change events
      const subscription = AppState.addEventListener('change', onAppStateChange)
 
      return () => {
        subscription.remove()
      }
    }
  }}
>
  <App>
</SWRConfig>

For initReconnect, it requires some 3rd party libraries such as NetInfo  to subscribe to the network status. The implementation will be similar to the example above: receiving a callback function and trigger it when the network recovers from offline, so SWR can start a revalidation to keep your data up-to-date.