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. Beware: If your app shows an opened Modal, BackHandler will not publish any events (see Modal docs).

Example:

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;

});

Lifecycle example:

componentDidMount() {

this.backHandler = BackHandler.addEventListener('hardwareBackPress', this.handleBackPress);

}

componentWillUnmount() {

this.backHandler.remove()

}

handleBackPress = () => {

this.goBack(); // works best when the goBack is async

return true;

}

Lifecycle alternative:

componentDidMount() {

this.backHandler = BackHandler.addEventListener('hardwareBackPress', () => {

this.goBack(); // works best when the goBack is async

return true;

});

}

componentWillUnmount() {

this.backHandler.remove();

}

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Reference

Methods

addEventListener()

static addEventListener(eventName, handler)

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exitApp()

static exitApp()

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removeEventListener()

static removeEventListener(eventName, handler)