I'm trying to create live dashboard mobile app with react-native. I setInterval to fetch data every 5 sec. When i go to other actions i clearIntervar(cause if i don't clear it continues other pages) and it's ok but when i try to Action.pop() i cant setInterval again.
I tried to setInterval in componentWillUnmount() and Action.refresh(with same props) but every time; i get the same error.
Warning: Can't perform a React state update on an unmounted component.
This is a no-op, but it indicates a memory leak in your application.
To fix, cancel all subscriptions and asynchronous tasks in the
componentWillUnmount method.
This is the sample like my code:
export default class MyComponent extends Component {
constructor(props) {
super(props);
this.state = {
isRefresh: false
}
}
componentDidMount() {
this.getData()
}
async getData() {
//just a sample
const data = await fetch(url).then((response) => response.json());
this.setState({data: data});
if (this.state.isRefresh) {
const intervalId = setInterval(() => {
this.getData();
}, 5000);
this.setState({
intervalId: intervalId,
isRefresh: true
})
}
}
render() {
return (
<View>
<Text>{this.state.data}</Text>
<Button onPress={() => {
clearInterval(this.state.intervalId);
Action.otherPage();
}
} title={'Test Button'}/>
</View>
)
}
}
I have to setInterval and fetch data in the other pages too. So i need to clear when i go to other pages and need to setInterval when i come back with Actions.pop()
Don't store intervalId in state, instead you should make use of instance variable for your interval,
constructor(props) {
super(props);
this.state = {
isRefresh: false
}
this.intervalId = null; //instance variable
}
Then assign your interval to instance variable,
this.intervalId = setInterval(() => { this.getData();}, 5000);
Then use componentWillUnmount to clear interval,
componentWillUnmount(){
clearInterval(this.intervalId);
}
Please use this
componentDidMount() {
const { navigation } = this.props;
this.focusListener = navigation.addListener('didFocus', () => {
// The screen is focused
// Call any action you want when a user on this screen
});
}
componentWillUnmount() {
// Remove the event listener
this.focusListener.remove();
}
I have an Animated.timing and I want to stop it when the user navigate to another app, is this possible?
you can use AppState like this:
import React, {Component} from "react"
import {AppState, View} from "react-native"
class YourClass extends Component {
state = {
appState: AppState.currentState
}
componentDidMount() {
//add a listener here
AppState.addEventListener("change", this._handleAppStateChange);
}
componentWillUnmount() {
// remember add this line
AppState.removeEventListener("change", this._handleAppStateChange);
}
_handleAppStateChange = (nextAppState) => {
if (this.state.appState.match(/inactive|background/) && nextAppState === "active"){
console.log("App has come to the foreground!")
}else{
//here you can call stop animation function
}
this.setState({appState: nextAppState});
}
render() {
return (
<Text>Current state is: {this.state.appState}</Text>
);
}
}
How to show React Native Homepage if is connected?
and if is not connected, Show a full screen photo? (with a Condition by NetInfo)
import React, {Component} from 'react';
import {
Platform,
StyleSheet,
Text,
View,
NetInfo
} from 'react-native';
function ConnectionOk() {
return (
<View >
<Text >
Welcome to React Native1!
</Text>
<Text >
To get started, edit App.js
</Text>
</View>
);
}
function ConnectionNotOk() {
return (
<View>
<Text>not Connected ...</Text>
</View>
);
}
type Props = {};
export default class App extends Component<Props> {
constructor(props) {
super(props)
this.state = {
isConnected: false,
isMounted: true
};
}
componentDidMount() {
// my way of checking internet, don't use both methods
// this.checkInternetConnection();
// Its good idea to attach event listener here, or in constructor
NetInfo.isConnected.addEventListener(
'connectionChange',
this.handleFirstConnectivityChange
);
};
componentWillUnmount() {
this.setState({
isMounted: false
});
// Its good idea to remove all event listener here
NetInfo.removeEventListener(
'connectionChange',
this.handleFirstConnectivityChange
);
};
checkInternetConnection() {
fetch("https://httpbin.org/ip")
.then(response => response.json())
.then(responseJson => {
//update the state only when component is mounted, else it will throw warning
if (this.state.isMounted) {
this.setState({
isConnected: true
});
}
}).catch(err => {
// No internet, redirect to some action if required
})
};
handleFirstConnectivityChange(isConnected) {
if (isConnected) {
this.setState({
isConnected: true
});
} else {
//redirect to some route if required
return <ConnectionNotOk />;
}
render() {
return this.state.isConnected ? < ConnectionOk /> : < ConnectionNotOk />
}
};
}
You can use some flag variable in component state.
From my experience I can say that NetInfo doesn't always gives correct info. ex Internet data is on but no internet connection, NetInfo will return true.
I handle this case by fetching some http api (say https://httpbin.org/ip) which is light and gives correct info about internet.
Also its a good idea to define,add/remove listeners in their appropriate places instead of render.
Try following:
type Props = {};
export default class App extends Component < Props > {
constructor(props) {
super(props)
this.state = {
isConnected: false,
isMounted: true
};
this.checkInternetConnection = this.checkInternetConnection.bind(this);
this.handleFirstConnectivityChange = this.handleFirstConnectivityChange.bind(this);
}
componentDidMount() {
// my way of checking internet, don't use both methods
// this.checkInternetConnection();
// Its good idea to attach event listener here, or in constructor
NetInfo.isConnected.addEventListener(
'connectionChange',
this.handleFirstConnectivityChange
);
}
componentWillUnmount() {
this.setState({
isMounted: false
});
// Its good idea to remove all event listener here
NetInfo.removeEventListener(
'connectionChange',
this.handleFirstConnectivityChange
);
}
checkInternetConnection() {
fetch("https://httpbin.org/ip")
.then(response => response.json())
.then(responseJson => {
//update the state only when component is mounted, else it will throw warning
if (this.state.isMounted) {
this.setState({
isConnected: true
});
}
}).catch(err => {
// No internet, redirect to some action if required
})
}
handleFirstConnectivityChange(isConnected) {
if (isConnected) {
this.setState({
isConnected: true
});
} else {
//redirect to some route if required
//return <ConnectedNotOk / > ;
}
}
render() {
return (
this.state.isConnected ? <ConnectionOk /> : <ConnectionNotOk />
);
}
}
My full example code.
NetInfo.isConnected.fetch().then(isConnected => {
console.log('First, is ' + (isConnected ? 'online' : 'offline'));
});
function handleFirstConnectivityChange(isConnected) {
console.log('Then, is ' + (isConnected ? 'online' : 'offline'));
if (isConnected == false) {
// your image
}
else{
Actions.HomePage() //if connected go to homepage
}
NetInfo.isConnected.removeEventListener(
'connectionChange',
handleFirstConnectivityChange
);
}
NetInfo.isConnected.addEventListener(
'connectionChange',
handleFirstConnectivityChange
);
i am using react-native-router-flux for redirection
You can achieve it by having isConnected flag in state and using network code set it to true or false dynamically. Then inside the render function use below code
{ this.state.isConnected &&
// Your UI code here
}
I have made some changes in your code. Hope it will help you. Please find complete code below:
import React, {Component} from 'react';
import {
Platform,
StyleSheet,
Text,
View,
NetInfo
} from 'react-native';
export default class App extends Component {
constructor(props) {
super(props)
this.state = {
isConnected: false,
isMounted: true
};
}
componentWillMount() {
NetInfo.addEventListener(
'connectionChange',
this.handleFirstConnectivityChange
);
}
componentWillUnmount() {
this.setState({
isMounted: false
});
// Its good idea to remove all event listener here
NetInfo.removeEventListener(
'connectionChange',
this.handleFirstConnectivityChange
);
}
handleFirstConnectivityChange(connectionInfo) {
if(connectionInfo.type && connectionInfo.type != "none"){
this.setState({
isConnected: true
});
}else {
this.setState({
isConnected: false
});
}
}
render () {
return (
<View>
{this.state.isConnected &&
<View >
<Text >
Welcome to React Native1!
</Text>
<Text >
To get started, edit App.js
</Text>
</View>
}
{!this.state.isConnected &&
<View>
<Text>not Connected ...</Text>
</View>
}
</View>
)
}
}
I create a simple app that using React Native AppState:
import React, {Component} from 'react'
import {AppState, Text , View} from 'react-native'
export default class AppStateExample extends React.Component {
constructor(props){
super(props);
this.state = {
name:'not change'
}
}
componentDidMount() {
AppState.addEventListener('change', this._handleAppStateChange);
}
componentWillUnmount() {
AppState.removeEventListener('change', this._handleAppStateChange);
}
_handleAppStateChange = (nextAppState) => {
if(AppState.currentState=='background'){
console.log('background mode');
this.setState({name:'back'});
}
if(AppState.currentState =='active'){
//...
}
};
render() {
return (
<View>
<Text>State Name : {this.state.name}</Text>
</View>
);
}
}
And when I try switch app from foreground to background and then background to foreground console.log('background mode'); work very well and console
print 'background mode'
BUT
The this.setState({name:'back'}); not working and I see 'not change' text in view
Actually, based on React Native Docs on AppState change for Functional Component I prefer to write code like below:
import { useRef, useState, useEffect } from "react";
import { AppState } from "react-native";
const AppStateManager = () => {
const appState = useRef(AppState.currentState);
const [appStateVisible, setAppStateVisible] = useState(appState.current);
useEffect(() => {
AppState.addEventListener("change", handleAppStateChange);
return () => {
AppState.removeEventListener("change", handleAppStateChange);
};
}, []);
const handleAppStateChange = (nextAppState) => {
if (
appState.current.match(/inactive|background/) &&
nextAppState === "active"
) {
console.log("App has come to the foreground!");
}
appState.current = nextAppState;
setAppStateVisible(appState.current);
console.log("AppState", appState.current);
};
return null;
};
export default AppStateManager;
Surely, we can use this component in the root of the project just like a React Component:
~~~
<App>
~~
<AppStateManager />
~~
.
.
.
It is because, AppState.addEventListener('change', this._handleAppStateChange); is too late to register.
You probably want to listen AppState the first thing in your app before main components get loaded and pass down the values probably by your state management library
I would go for a switch that wrap all endPoint
note: to get appState status AppState.currentState
this.state = {
appState: AppState.currentState
// https://facebook.github.io/react-native/docs/appstate.html
};
componentWillMount() {
AppState.addEventListener('change', () => this._handleAppStateChange());
};
componentWillUnmount() {
AppState.removeEventListener('change', () => this._handleAppStateChange());
}
_handleAppStateChange() {
// https://facebook.github.io/react-native/docs/appstate.html
const {
appState
} = this.state;
console.warn({
appState
})
this.fetchData().catch(error => error);
switch (appState) {
case 'active': //The app is running in the foreground
this.onStart();
break;
case 'background': // The app is running in the background. The user is either
this.onEnd();
console.warn('background');
break;
case 'inactive':
// The app transitioning between foreground & background or entering the Multitasking view or in the event of an incoming call
console.warn('Inactive');
break;
default:
console.warn('_handleAppStateChange default');
}
}
I want to check if there are more than one screens are on stack when device back button is hit. If yes, I want to show previous screen and if no, I want to exit app.
I have checked number of examples but those use BackAndroid and Navigator. But both of them are deprecated. BackHandler is replacement for BackAndroid. And I can show previous screen by using props.navigation.goBack(null).
But I am unable to find code for finding screen count in stack. I don't want to use deprecated Navigator!
This example will show you back navigation which is expected generally in most of the flows. You will have to add following code to every screen depending on expected behavior. There are 2 cases:
1. If there are more than 1 screen on stack, device back button will show previous screen.
2. If there is only 1 screen on stack, device back button will exit app.
Case 1: Show previous screen
import { BackHandler } from 'react-native';
constructor(props) {
super(props)
this.handleBackButtonClick = this.handleBackButtonClick.bind(this);
}
componentWillMount() {
BackHandler.addEventListener('hardwareBackPress', this.handleBackButtonClick);
}
componentWillUnmount() {
BackHandler.removeEventListener('hardwareBackPress', this.handleBackButtonClick);
}
handleBackButtonClick() {
this.props.navigation.goBack(null);
return true;
}
Important: Don't forget to bind method in constructor and to remove listener in componentWillUnmount.
Case 2: Exit App
In this case, no need to handle anything on that screen where you want to exit app.
Important: This should be only screen on stack.
In functional component:
import { BackHandler } from "react-native";
function handleBackButtonClick() {
navigation.goBack();
return true;
}
useEffect(() => {
BackHandler.addEventListener("hardwareBackPress", handleBackButtonClick);
return () => {
BackHandler.removeEventListener("hardwareBackPress", handleBackButtonClick);
};
}, []);
import { BackHandler } from 'react-native';
constructor() {
super();
this.handleBackButtonClick = this.handleBackButtonClick.bind(this);
}
componentWillMount() {
BackHandler.addEventListener('hardwareBackPress', this.handleBackButtonClick);
}
componentWillUnmount() {
BackHandler.removeEventListener('hardwareBackPress', this.handleBackButtonClick);
}
handleBackButtonClick() {
//this.props.navigation.goBack(null);
BackHandler.exitApp();
return true;
}
handleBackButtonClick() {
return true; // when back button don't need to go back
}
In Functional Component
import { BackHandler } from 'react-native';
function handleBackButtonClick() {
navigation.goBack();
return true;
}
useEffect(() => {
BackHandler.addEventListener('hardwareBackPress', handleBackButtonClick);
return () => {
BackHandler.removeEventListener('hardwareBackPress', handleBackButtonClick);
};
}, []);
In a case where there are more than one screens stacked in the stack, the default back button behavior in react-native is to navigate back to the previous screen in the stack. Handling the device back button press when having only one screen to exit the app requires a custom setting. Yet this can be achieved without having to add back handling code to each and every screen by modifying the getStateForAction method of the particular StackNavigator's router.
Suppose you have the following StackNavigator used in the application
const ScreenStack = StackNavigator(
{
'Screen1': {
screen: Screen1
},
'Screen2': {
screen: Screen2
},
},
{
initialRouteName: 'Screen1'
}
);
The getStateForAction method of the stack navigator's router can be modified as follows to achieve the expected back behavior.
const defaultStackGetStateForAction =
ScreenStack.router.getStateForAction;
ScreenStack.router.getStateForAction = (action, state) => {
if(state.index === 0 && action.type === NavigationActions.BACK){
BackHandler.exitApp();
return null;
}
return defaultStackGetStateForAction(action, state);
};
the state.index becomes 0 only when there is one screen in the stack.
Here is how I implemented successfully using certain condition:
componentWillMount() {
BackHandler.addEventListener(
'hardwareBackPress',
this.handleBackButtonClick,
);
}
componentWillUnmount() {
BackHandler.removeEventListener(
'hardwareBackPress',
this.handleBackButtonClick,
);
}
handleBackButtonClick = () => {
//some condition
if (this.state.isSearchBarActive) {
this.setState({
isSearchBarActive: false,
});
this.props.navigation.goBack(null);
return true;
}
return false;
};
React Native Hooks has a nice useBackHandler hook which simplifies the process of setting up event listeners for Android back button.
import { useBackHandler } from '#react-native-community/hooks'
useBackHandler(() => {
if (shouldBeHandledHere) {
// handle it
return true
}
// let the default thing happen
return false
})
try this
react navigation
componentDidMount() {
BackHandler.addEventListener('hardwareBackPress', this.handleBackButton);
}
handleBackButton = () => {
const pushAction = StackActions.push({
routeName: 'DefaultSelections',
});
this.props.navigation.dispatch(pushAction);
}
current screen is "DefaultSelections" , on back button press, would be shifted on to the same and hence back button disabled work around, as disabling back button by
return true
for backButton ( as suggested by the official docs ) disables back button on all screens ; not wanted
an utility function could be very helpful:
backPressHandler.js
import React from 'react';
import {BackHandler} from 'react-native';
const onBackPress = (callback) => {
BackHandler.addEventListener('hardwareBackPress', callback);
return () => {
BackHandler.removeEventListener('hardwareBackPress', callback);
};
};
export {onBackPress};
now in my screen:
myScreen.js
import {onBackPress} from '../utils/backPressHandler';
function handleBackPress() {
navigation.goBack();
return true;
}
useEffect(() => {
onBackPress(handleBackPress);
}, []);
I am on v0.46.0 of react-native and had the same issue. I tracked the issue down to this file in the react-native code base
https://github.com/facebook/react-native/blob/master/Libraries/Utilities/BackHandler.android.js#L25
When running with the chrome debugger turned off the line
var subscriptions = Array.from(_backPressSubscriptions.values()).reverse()
always returns an empty array for subscriptions which in turn causes the invokeDefault variable to stay true and the .exitApp() function to be called.
After more investigation, I think the issue was discovered and discussed in the following PR #15182.
Even after copy/pasting the PR change in an older version of RN it did not work most likely caused by the issue described in the PR.
After some very slight modifications I got it working by changing to
RCTDeviceEventEmitter.addListener(DEVICE_BACK_EVENT, function() {
var invokeDefault = true;
var subscriptions = []
_backPressSubscriptions.forEach(sub => subscriptions.push(sub))
for (var i = 0; i < subscriptions.reverse().length; ++i) {
if (subscriptions[i]()) {
invokeDefault = false;
break;
}
}
if (invokeDefault) {
BackHandler.exitApp();
}
});
Simply using a .forEach which was the original implementation on the PR before the amended Array.from syntax works throughout.
So you could fork react-native and use a modified version, submit a PR though I imagine that will take a little while to be approved and merged upstream, or you can do something similar to what I did which was to override the RCTDeviceEventEmitter.addListener(...) for the hardwareBackPress event.
// other imports
import { BackHandler, DeviceEventEmitter } from 'react-native'
class MyApp extends Component {
constructor(props) {
super(props)
this.backPressSubscriptions = new Set()
}
componentDidMount = () => {
DeviceEventEmitter.removeAllListeners('hardwareBackPress')
DeviceEventEmitter.addListener('hardwareBackPress', () => {
let invokeDefault = true
const subscriptions = []
this.backPressSubscriptions.forEach(sub => subscriptions.push(sub))
for (let i = 0; i < subscriptions.reverse().length; i += 1) {
if (subscriptions[i]()) {
invokeDefault = false
break
}
}
if (invokeDefault) {
BackHandler.exitApp()
}
})
this.backPressSubscriptions.add(this.handleHardwareBack)
}
componentWillUnmount = () => {
DeviceEventEmitter.removeAllListeners('hardwareBackPress')
this.backPressSubscriptions.clear()
}
handleHardwareBack = () => { /* do your thing */ }
render() { return <YourApp /> }
}
constructor(props){
super(props)
this.onBackPress = this.onBackPress.bind(this);
}
componentWillMount() {
BackHandler.addEventListener('hardwareBackPress', this.onBackPress);
}
componentWillUnmount(){
BackHandler.removeEventListener('hardwareBackPress', this.onBackPress);
}
onBackPress(){
const {dispatch, nav} = this.props;
if (nav.index < 0) {
return false;
}
dispatch(NavigationActions.back());
return true;
}
render(){
const {dispatch, nav} = this.props;
return(
<DrawerRouter
navigation= {
addNavigationHelpers({
dispatch,
state: nav,
addListener,
})
}
/>
);
}
If you use react-navigation, the other answers did not work for me but this did:
const handleGoBack = useCallback(() => {
// custom logic here
return true; // Returning true from onBackPress denotes that we have handled the event
}, [navigation]);
useFocusEffect(
React.useCallback(() => {
BackHandler.addEventListener('hardwareBackPress', handleGoBack);
return () =>
BackHandler.removeEventListener('hardwareBackPress', handleGoBack);
}, [handleGoBack]),
Here is the link to the documentation
useFocusEffect(
React.useCallback(() => {
const onBackPress = () => {
navigation.navigate('Journal');
return true;
};
BackHandler.addEventListener('hardwareBackPress', onBackPress);
return () => {
BackHandler.removeEventListener('hardwareBackPress', onBackPress);
};
}, []),
);
`
import { useFocusEffect} from '#react-navigation/native';
export default function App(props: any) {
function handleBackButton() {
navigation.goBack();
return true;
}
useFocusEffect(
React.useCallback(() => {
BackHandler.addEventListener("hardwareBackPress", handleBackButton);
return () => {
console.log("I am removed from stack")
BackHandler.removeEventListener("hardwareBackPress", handleBackButton);
};
}, [])
);
}
I used flux for navigation.
const RouterComp = () => {
let backLoginScene=false;
return (
<Router
backAndroidHandler={() => {
const back_button_prohibited = ['login','userInfo','dashboard'];
if (back_button_prohibited.includes(Actions.currentScene) ) {
if (backLoginScene == false) {
ToastAndroid.show("Click back again to exit.", ToastAndroid.SHORT);
backLoginScene = !backLoginScene;
setTimeout(() => {
backLoginScene = false;
}, 2000);
return true;
} else {
backLoginScene = false;
BackHandler.exitApp();
}
return false;
}}}>
<Scene key='root' hideNavBar>
<Scene key='guest' hideNavBar >
<Scene key='login' component={Login} ></Scene>
<Scene key='userInfo' component={UserInfo}></Scene>
</Scene>
<Scene key='user' hideNavBar>
<Scene key='dashboard' component={Dashboard} title='Dashboard' initial />
<Scene key='newAd' component={NewAd} title='New Ad' />
</Scene>
</Scene>
</Router>
)
}
export default RouterComp;