Fix 1405 handle android back button in composer (#1446)

* handle android back button in composer

* improve backHandler error handling

* simplify composer onClose functionality

src/view/com/composer/Composer.tsx

@@ -2,6 +2,7 @@ import React, {useCallback, useEffect, useMemo, useRef, useState} from 'react'
 import {observer} from 'mobx-react-lite'
 import {
   ActivityIndicator,
+  BackHandler,
   Keyboard,
   KeyboardAvoidingView,
   Platform,
@@ -49,14 +50,10 @@ import {SelectLangBtn} from './select-language/SelectLangBtn'
 import {EmojiPickerButton} from './text-input/web/EmojiPicker.web'
 import {insertMentionAt} from 'lib/strings/mention-manip'
 
-type Props = ComposerOpts & {
-  onClose: () => void
-}
-
+type Props = ComposerOpts
 export const ComposePost = observer(function ComposePost({
   replyTo,
   onPost,
-  onClose,
   quote: initQuote,
   mention: initMention,
 }: Props) {
@@ -90,6 +87,9 @@ export const ComposePost = observer(function ComposePost({
   const [labels, setLabels] = useState<string[]>([])
   const [suggestedLinks, setSuggestedLinks] = useState<Set<string>>(new Set())
   const gallery = useMemo(() => new GalleryModel(store), [store])
+  const onClose = useCallback(() => {
+    store.shell.closeComposer()
+  }, [store])
 
   const autocompleteView = useMemo<UserAutocompleteModel>(
     () => new UserAutocompleteModel(store),
@@ -129,6 +129,20 @@ export const ComposePost = observer(function ComposePost({
       onClose()
     }
   }, [store, onClose, graphemeLength, gallery])
+  // android back button
+  useEffect(() => {
+    const backHandler = BackHandler.addEventListener(
+      'hardwareBackPress',
+      () => {
+        onPressCancel()
+        return true
+      },
+    )
+
+    return () => {
+      backHandler.remove()
+    }
+  }, [onPressCancel])
 
   // initial setup
   useEffect(() => {