react-native/Libraries/Utilities/BackHandler.android.js

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/**
* 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 BackHandler
*/
'use strict';
var DeviceEventManager = require('NativeModules').DeviceEventManager;
var RCTDeviceEventEmitter = require('RCTDeviceEventEmitter');
var DEVICE_BACK_EVENT = 'hardwareBackPress';
type BackPressEventName = $Enum<{
backPress: string,
}>;
var _backPressSubscriptions = new Set();
RCTDeviceEventEmitter.addListener(DEVICE_BACK_EVENT, function() {
var backPressSubscriptions = new Set(_backPressSubscriptions);
var invokeDefault = true;
var subscriptions = [...backPressSubscriptions].reverse();
for (var i = 0; i < subscriptions.length; ++i) {
if (subscriptions[i]()) {
invokeDefault = false;
break;
}
}
if (invokeDefault) {
BackHandler.exitApp();
}
});
/**
* Detect hardware button presses for back navigation.
*
* Android: Detect hardware back button presses, and programmatically invoke the default back button
* functionality to exit the app if there are no listeners or if none of the listeners return true.
*
* tvOS: Detect presses of the menu button on the TV remote. (Still to be implemented:
* programmatically disable menu button handling
* functionality to exit the app if there are no listeners or if none of the listeners return true.)
*
* iOS: Not applicable.
*
* The event subscriptions are called in reverse order (i.e. last registered subscription first),
* and if one subscription returns true then subscriptions registered earlier will not be called.
*
* Example:
*
* ```javascript
* BackHandler.addEventListener('hardwareBackPress', function() {
* // this.onMainScreen and this.goBack are just examples, you need to use your own implementation here
* // Typically you would use the navigator here to go to the last state.
*
* if (!this.onMainScreen()) {
* this.goBack();
* return true;
* }
* return false;
* });
* ```
*/
var BackHandler = {
exitApp: function() {
DeviceEventManager.invokeDefaultBackPressHandler();
},
addEventListener: function (
eventName: BackPressEventName,
handler: Function
): {remove: () => void} {
_backPressSubscriptions.add(handler);
return {
remove: () => BackHandler.removeEventListener(eventName, handler),
};
},
removeEventListener: function(
eventName: BackPressEventName,
handler: Function
): void {
_backPressSubscriptions.delete(handler);
},
};
module.exports = BackHandler;