react-native/website/versioned_docs/0.22/appstateios.md

id, title, original_id

id	title	original_id
version-0.22-appstateios	appstateios	appstateios

AppStateIOS #

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AppStateIOS can tell you if the app is in the foreground or background, and notify you when the state changes.

AppStateIOS is frequently used to determine the intent and proper behavior when handling push notifications.

iOS App States #

• active - The app is running in the foreground
• background - The app is running in the background. The user is either in another app or on the home screen
• inactive - This is a transition state that currently never happens for typical React Native apps.

For more information, see Apple's documentation

Basic Usage #

To see the current state, you can check AppStateIOS.currentState, which will be kept up-to-date. However, currentState will be null at launch while AppStateIOS retrieves it over the bridge.

getInitialState: function() { return { currentAppState: AppStateIOS.currentState, }; }, componentDidMount: function() { AppStateIOS.addEventListener('change', this._handleAppStateChange); }, componentWillUnmount: function() { AppStateIOS.removeEventListener('change', this._handleAppStateChange); }, _handleAppStateChange: function(currentAppState) { this.setState({ currentAppState, }); }, render: function() { return ( <Text>Current state is: {this.state.currentAppState}</Text> ); },

This example will only ever appear to say "Current state is: active" because the app is only visible to the user when in the active state, and the null state will happen only momentarily.

Methods #

static addEventListener(type: string, handler: Function) #

Add a handler to AppState changes by listening to the change event type and providing the handler

static removeEventListener(type: string, handler: Function) #

Remove a handler by passing the change event type and the handler

Properties #

currentState: TypeCastExpression #

// TODO: getCurrentAppState callback seems to be called at a really late stage // after app launch. Trying to get currentState when mounting App component // will likely to have the initial value here. // Initialize to 'active' instead of null.

Examples #

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'use strict';

var React = require('react-native'); var { AppStateIOS, Text, View } = React;

var AppStateSubscription = React.createClass({ getInitialState() { return { appState: AppStateIOS.currentState, previousAppStates: [], memoryWarnings: 0, }; }, componentDidMount: function() { AppStateIOS.addEventListener('change', this._handleAppStateChange); AppStateIOS.addEventListener('memoryWarning', this._handleMemoryWarning); }, componentWillUnmount: function() { AppStateIOS.removeEventListener('change', this._handleAppStateChange); AppStateIOS.removeEventListener('memoryWarning', this._handleMemoryWarning); }, _handleMemoryWarning: function() { this.setState({memoryWarnings: this.state.memoryWarnings + 1}); }, _handleAppStateChange: function(appState) { var previousAppStates = this.state.previousAppStates.slice(); previousAppStates.push(this.state.appState); this.setState({ appState, previousAppStates, }); }, render() { if (this.props.showMemoryWarnings) { return ( <View> <Text>{this.state.memoryWarnings}</Text> </View> ); } if (this.props.showCurrentOnly) { return ( <View> <Text>{this.state.appState}</Text> </View> ); } return ( <View> <Text>{JSON.stringify(this.state.previousAppStates)}</Text> </View> ); } });

exports.title = 'AppStateIOS'; exports.description = 'iOS app background status'; exports.examples = [ { title: 'AppStateIOS.currentState', description: 'Can be null on app initialization', render() { return <Text>{AppStateIOS.currentState}</Text>; } }, { title: 'Subscribed AppStateIOS:', description: 'This changes according to the current state, so you can only ever see it rendered as "active"', render(): ReactElement { return <AppStateSubscription showCurrentOnly={true} />; } }, { title: 'Previous states:', render(): ReactElement { return <AppStateSubscription showCurrentOnly={false} />; } }, { title: 'Memory Warnings', description: 'In the simulator, hit Shift+Command+M to simulate a memory warning.', render(): ReactElement { return <AppStateSubscription showMemoryWarnings={true} />; } }, ];

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