Using useRef to make a tap on a container ScrollView put focus in a TextInput - react-native

Question

This is for a React Native app.
One of my screens has a ScrollView wrapped around a TextInput. The ScrollView has a lot of height - moreso than the TextInput when it's blank - so the behavior I want is that if a user taps on any of the 'blank space' in the ScrollView, it will put focus in the TextInput.
The code I have so far boils down to this:
export function MainInput() {
const ref_textinput = useRef();
const onTapScrollViewBody = () => {
console.log("Detected tap")
ref_textinput.current?.focus()
}
return (
<TouchableWithoutFeedback onPress={onTapScrollViewBody}>
<ScrollView style={styles.parentScrollView}>
<TextInput
ref={ref_textinput}
...
It's not working unfortunately. When focus isn't in the TextInput, the first time I tap in the blank space of the ScrollView, I do see the console log, but focus doesn't go into the TextInput, nor do further taps on the blank space trigger more console logs. However, tapping into the TextInput (which obviously puts focus back on it) then tapping back out will trigger the console log.
Am I misunderstanding how useRef works here?

Answer 1

Your understanding of useRef is fine, it's the understanding of the ScrollView that needs some help. If two elements that share coordinates are touchable, React Native will give the touch to the "top" element (whether by z-index, render order, etc). Your example creates the following hierarchy:
|-TouchableWithoutFeedback
|-ScrollView
|-TextInput
If you press within the TextInput's area, it will always capture the touch, as you found. If you press within the ScrollView's area, but outside of the text input, your touch is captured by the ScrollView, which will try to use your touch to scroll it. Only when you touch outside the ScrollView should your TouchableWithoutFeedback activate.
You still want the ScrollView to scroll, so when do you want your tap to focus the text input? You could delete your Touchable and use an event exposed by ScrollView, like
<ScrollView
onScrollEndDrag={() => ref_textinput.current?.focus()}
// and/or
onMomentumScrollEnd={() => ref_textinput.current?.focus()}
...
A solution that would handle tapping differently from scrolling could be achieved using react-native-gesture-handler, but it would be more involved.