add useBackHandler for android

Author: pvinis

README.md

@@ -21,6 +21,7 @@ yarn add react-native-hooks
 ## API
 - [useAccessibilityInfo](https://github.com/react-native-community/react-native-hooks#useaccessibilityinfo)
 - [useAppState](https://github.com/react-native-community/react-native-hooks#useappstate)
+- [useBackHandler](https://github.com/react-native-community/react-native-hooks#usebackhandler)
 - [useCameraRoll](https://github.com/react-native-community/react-native-hooks#usecameraroll)
 - [useClipboard](https://github.com/react-native-community/react-native-hooks#useclipboard)
 - [useDimensions](https://github.com/react-native-community/react-native-hooks#usedimensions)
@@ -47,6 +48,21 @@ import { useAppState } from 'react-native-hooks'
 const currentAppState = useAppState()
 ```
 
+### `useBackHandler`
+
+```js
+import { useBackHandler } from 'react-native-hooks'
+
+useBackHandler(() => {
+  if (shouldBeHandledHere) {
+    // handle it
+    return true
+  }
+  // let the default thing happen
+  return false
+})
+```
+
 ### `useCameraRoll`
 
 ```js

index.js

@@ -1,5 +1,6 @@
 import useDimensions from './lib/useDimensions'
 import useAppState from './lib/useAppState'
+import useBackHandler from './lib/useBackHandler'
 import useCameraRoll from './lib/useCameraRoll'
 import useClipboard from './lib/useClipboard'
 import useAccessibilityInfo from './lib/useAccessibilityInfo'
@@ -12,6 +13,7 @@ import useDeviceOrientation from './lib/useDeviceOrientation'
 export {
   useDimensions,
   useAppState,
+  useBackHandler,
   useCameraRoll,
   useClipboard,
   useAccessibilityInfo,

lib/useBackHandler.js

@@ -0,0 +1,13 @@
+import React, { useEffect, useState } from 'react'
+import { BackHandler } from 'react-native'
+
+
+export default (handler) => {
+  useEffect(() => {
+    BackHandler.addEventListener('hardwareBackPress', handler)
+
+    return () => {
+      BackHandler.removeEventListener('hardwareBackPress', handler)
+    }
+  })
+}