hide keyboard when backgrounding (#8450)

src/view/com/composer/Composer.tsx

@@ -64,6 +64,7 @@ import {
   type SupportedMimeTypes,
 } from '#/lib/constants'
 import {useAnimatedScrollHandler} from '#/lib/hooks/useAnimatedScrollHandler_FIXED'
+import {useAppState} from '#/lib/hooks/useAppState'
 import {useIsKeyboardVisible} from '#/lib/hooks/useIsKeyboardVisible'
 import {useNonReactiveCallback} from '#/lib/hooks/useNonReactiveCallback'
 import {usePalette} from '#/lib/hooks/usePalette'
@@ -822,6 +823,8 @@ let ComposerPost = React.memo(function ComposerPost({
     [post.id, onSelectVideo, onImageAdd, _],
   )
 
+  useHideKeyboardOnBackground()
+
   return (
     <View
       style={[
@@ -1522,6 +1525,18 @@ function isEmptyPost(post: PostDraft) {
   )
 }
 
+function useHideKeyboardOnBackground() {
+  const appState = useAppState()
+
+  useEffect(() => {
+    if (isIOS) {
+      if (appState === 'inactive') {
+        Keyboard.dismiss()
+      }
+    }
+  }, [appState])
+}
+
 const styles = StyleSheet.create({
   topbarInner: {
     flexDirection: 'row',