React Native: Determine number of lines of Text component
I want to provide a modern solution. There is now a onTextLayout
event that includes an array of lines
which can be determined what number of lines are being rendered. There's other details in the lines
array like actual height and width of every line which can be further used to determine if the text is being truncated.
const NUM_OF_LINES = 5;const SOME_LONG_TEXT_BLOCK = 'Lorem ipsum ...';function SomeComponent () { const [ showMore, setShowMore ] = useState(false); const onTextLayout = useCallback(e => { setShowMore(e.nativeEvent.lines.length > NUM_OF_LINES); }, []); return ( <Text numberOfLines={NUM_OF_LINES} onTextLayout={onTextLayout}> {SOME_LONG_TEXT_BLOCK} </Text> );}
It looks like React Native 0.24 implements an onLayout function
http://facebook.github.io/react-native/docs/text.html#onlayout
onLayout function
Invoked on mount and layout changes with
{nativeEvent: {layout: {x, y, width, height}}}
So it looks like you could pass an onLayout callback function, get the height of the Text component and then do some calculations using the line height to get to the number of lines
This one is working for both IOS AND Android
const [ loadMore, setLoadMore ] = useState(false); const [ numOfLines, setNumOfLines ] = useState(0); const onTextLayout = useCallback(e => { if(numOfLines == 0) setNumOfLines(e.nativeEvent.lines.length); }); const onLoadMoreToggle = () => { setLoadMore(!loadMore); } return ( <View style={styles.container}> <Text numberOfLines={numOfLines == 0 ? null : loadMore ? numOfLines : NUM_OF_LINES} onTextLayout={onTextLayout} style={styles.bodyText} > {props.children} </Text> { (numOfLines > NUM_OF_LINES) && <View style={styles.linkContainer}> <TouchableRipple onPress={onLoadMoreToggle}> <Text style={styles.linkText}>{ loadMore? 'Load Less' :'Load More'}</Text> </TouchableRipple> </View> } </View> )const styles = StyleSheet.create({ container: { display: 'flex', flexDirection:'column', }, bodyText: { flex:1, }, linkContainer: { flexDirection: 'row', justifyContent: 'flex-end' }, linkText: { color: '#2196f3' }})