Truncate Text - React Native

Question

I have a React Native app with a FlatList.

My logic that I have added was whenever the Character at 100th position is not empty an Expand/Collapse arrow should be added as shown below. NO arrow icon for short messages.

Well, this is bad logic!! Now when I change my app font to Large/small this logic won't work. It doesn't work for Chinese characters too LOL. So it shouldn't be based on number of characters.

{  alert.charAt(100) !== "" ?
                arrowClicked === true ? 
                <Icon type='materialicons' name='arrow-drop-up' onPress={()=>{this.setFullLength()}}  />
                : 
                <Icon type='materialicons' name='arrow-drop-down' onPress={()=>{this.setFullLength()}}  />
                : null
            } 

It should detect that the text is long and being truncated. How can I implement this?? Please Help!!!!

Answer 1

You should use the onTextLayout and decide the line length using something like below.

function CustomText(props) {
  const [showMore, setShowMore] = React.useState(false);
  const [lines, setLines] = React.useState(props.numberOfLines);

  const onTextLayout = (e) => {
    setShowMore(
      e.nativeEvent.lines.length > props.numberOfLines && lines !== 0
    );
  };

  return (
    <View>
      <Text numberOfLines={lines} onTextLayout={onTextLayout}>
        {props.children}
      </Text>
      {showMore && (
        <Button title="Show More"
          onPress={() => {
            setLines(0);
            setShowMore(false);
          }}
        />
      )}
      {!showMore && (
        <Button title="Hide More"
          onPress={() => {
            setLines(props.numberOfLines);
          }}
        />
      )}
    </View>
  );
}

Usage

  const text =
    'Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industrys standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to mak';

 <CustomText numberOfLines={2}>{text}</CustomText>

You can pass other props like styles as well.