score:-3

As a simple method , we can use componentWillUnmount() inside the root component for detect the app is closed. Because Root component Unmount only when app is closed. :)

score:0

Just ran into this same issue. The answer that's accepted does not actually do what is asked in the OP.

A hacky solution would be to set a flag on the first screen your application opens when opened fresh and to NOT SHOW THAT SCREEN when the app has just been backgrounded.

Not super elegant and I can't show example code, but it fixes my particular issue.

score:0

With @react-native-community/hooks you can use the useAppState hook to check the app state.

When you close the app, it gets a state of unknown once you open it back. When is in background, it says background' or 'inactive'. So when it's unknown` you know the app is opening from being closed, not minimized or in the background.

score:1

I suggest to use web socket and it will help you to solve your problem, as following :

react native app

import React from 'react';
const io = require('socket.io-client/dist/socket.io');

const App = ()=>{
    React.useEffect(()=>{
        // connect to web socket
        window.appSocket = io.connect(`<server-origin>/?token=<string>&userAppId=<string>`);
        window.appSocket.on('connect',()=>{
            // do what you line
        })
    },[])

    ...
}
export default App; 

express server side

const express   = require('express');
const server    = express();
const http      = require('http').Server(server);
const io        = require('socket.io')(http);
io.on('connection',(socket)=>{ // this callback function for each web socket connection
    let { token , userAppId } = socket.handshake.query;
    if( userAppId ){ 
        console.log(`${userAppId} online`)
        socket.on('disconnect',(resean)=>{
            console.log(`${userAppId} shut down`)
        })
    }
});

for more details, you can check socket.io

score:27

Looks like you can detect the previous state and compare it to the next state. You can't detect that the app is closing vs going into the background, from what I can find online, but you can detect if it was inactive (closed), or in the background.

Example from React Native Docs

import React, {Component} from 'react'
import {AppState, Text} from 'react-native'

class AppStateExample extends Component {

  state = {
    appState: AppState.currentState
  }

  componentDidMount() {
    AppState.addEventListener('change', this._handleAppStateChange);
  }

  componentWillUnmount() {
    AppState.removeEventListener('change', this._handleAppStateChange);
  }

  _handleAppStateChange = (nextAppState) => {
    if (this.state.appState.match(/inactive|background/) && nextAppState === 'active') {
      console.log('App has come to the foreground!')
    }
    this.setState({appState: nextAppState});
  }

  render() {
    return (
      <Text>Current state is: {this.state.appState}</Text>
    );
  }

}

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