2 column layout with flexBox on React Native

I'm trying to do a two column layout in React Native from a list of items. It only seems to work if I define the width of the items, I would like to define just a percentage of the parent width (0.5 would make a 2 column layout, but 0.25 would make a 4 column one). Can this be done?

export default class App extends Component {
  render() {
    return (
      <View style={[styles.container, {width:width}]}>
        <View style={styles.item}><Text>{'item1'}</Text></View>
        <View style={styles.item}><Text>{'item2'}</Text></View>
        <View style={styles.item}><Text>{'item3'}</Text></View>
        <View style={styles.item}><Text>{'item4'}</Text></View>
        <View style={styles.item}><Text>{'item4'}</Text></View>
        <View style={styles.item}><Text>{'item5'}</Text></View>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    flexDirection: 'row',
    flexWrap: 'wrap',
  },
  item :{
    flex: 0.5, //why this doesnt work???
    // width: 150, //using fixed item width instead of flex: 0.5 works
    height: 100,
    padding: 10,
    backgroundColor: 'red',
    // flexGrow: 1,
    // flexShrink: 0,
  }
});

You can play with it here: https://snack.expo.io/SyBjQuRxm

Css working equivalent: https://codepen.io/klamping/pen/WvvgBX?editors=110

Obviously I could do something like creating a container for each column, but that's not the point:

render() {
    return (
      <View style={[styles.container, {width:width}]}>
        <View style={styles.column1}>
             <View style={styles.item}><Text>{'item1'}</Text></View>
             <View style={styles.item}><Text>{'item2'}</Text></View>
             <View style={styles.item}><Text>{'item3'}</Text></View>
        </View>
        <View style={styles.column2}>
             <View style={styles.item}><Text>{'item4'}</Text></View>
             <View style={styles.item}><Text>{'item4'}</Text></View>
             <View style={styles.item}><Text>{'item5'}</Text></View>
        </View>
      </View>
    );
  }

It is possible if you use percentage values for the widths:

<View style={styles.container}>
  <View style={styles.item}>
    ...
  </View>
</View>

const styles = StyleSheet.create({
  container: {
    flex: 1,
    flexDirection: 'row',
    flexWrap: 'wrap',
    alignItems: 'flex-start' // if you want to fill rows left to right
  },
  item: {
    width: '50%' // is 50% of container width
  }
})