react-native/Libraries/AppState/AppState.js

167 lines
5.2 KiB
JavaScript

/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*
* @providesModule AppState
* @flow
*/
'use strict';
const NativeEventEmitter = require('NativeEventEmitter');
const NativeModules = require('NativeModules');
const RCTAppState = NativeModules.AppState;
const logError = require('logError');
const invariant = require('fbjs/lib/invariant');
/**
* `AppState` can tell you if the app is in the foreground or background,
* and notify you when the state changes.
*
* AppState is frequently used to determine the intent and proper behavior when
* handling push notifications.
*
* ### 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 state that occurs when transitioning between
* foreground & background, and during periods of inactivity such as
* entering the Multitasking view or in the event of an incoming call
*
* For more information, see
* [Apple's documentation](https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/TheAppLifeCycle/TheAppLifeCycle.html)
*
* ### Basic Usage
*
* To see the current state, you can check `AppState.currentState`, which
* will be kept up-to-date. However, `currentState` will be null at launch
* while `AppState` retrieves it over the bridge.
*
* ```
* getInitialState: function() {
* return {
* currentAppState: AppState.currentState,
* };
* },
* componentDidMount: function() {
* AppState.addEventListener('change', this._handleAppStateChange);
* },
* componentWillUnmount: function() {
* AppState.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.
*/
class AppState extends NativeEventEmitter {
_eventHandlers: Object;
currentState: ?string;
constructor() {
super(RCTAppState);
this._eventHandlers = {
change: new Map(),
memoryWarning: new Map(),
};
// TODO: Remove the 'active' fallback after `initialAppState` is exported by
// the Android implementation.
this.currentState = RCTAppState.initialAppState || 'active';
// TODO: this is a terrible solution - in order to ensure `currentState` prop
// is up to date, we have to register an observer that updates it whenever
// the state changes, even if nobody cares. We should just deprecate the
// `currentState` property and get rid of this.
this.addListener(
'appStateDidChange',
(appStateData) => {
this.currentState = appStateData.app_state;
}
);
// TODO: see above - this request just populates the value of `currentState`
// when the module is first initialized. Would be better to get rid of the prop
// and expose `getCurrentAppState` method directly.
RCTAppState.getCurrentAppState(
(appStateData) => {
this.currentState = appStateData.app_state;
},
logError
);
}
/**
* Add a handler to AppState changes by listening to the `change` event type
* and providing the handler
*
* TODO: now that AppState is a subclass of NativeEventEmitter, we could deprecate
* `addEventListener` and `removeEventListener` and just use `addListener` and
* `listener.remove()` directly. That will be a breaking change though, as both
* the method and event names are different (addListener events are currently
* required to be globally unique).
*/
addEventListener(
type: string,
handler: Function
) {
invariant(
['change', 'memoryWarning'].indexOf(type) !== -1,
'Trying to subscribe to unknown event: "%s"', type
);
if (type === 'change') {
this._eventHandlers[type].set(handler, this.addListener(
'appStateDidChange',
(appStateData) => {
handler(appStateData.app_state);
}
));
} else if (type === 'memoryWarning') {
this._eventHandlers[type].set(handler, this.addListener(
'memoryWarning',
handler
));
}
}
/**
* Remove a handler by passing the `change` event type and the handler
*/
removeEventListener(
type: string,
handler: Function
) {
invariant(
['change', 'memoryWarning'].indexOf(type) !== -1,
'Trying to remove listener for unknown event: "%s"', type
);
if (!this._eventHandlers[type].has(handler)) {
return;
}
this._eventHandlers[type].get(handler).remove();
this._eventHandlers[type].delete(handler);
}
}
AppState = new AppState();
module.exports = AppState;