我用的faltlist做的显示列表，后台传的是个list集合在前台让它显示。总是报要有唯一的key？

Question

这是问题：Warning: Each child in an array or iterator should have a unique "key" prop.这是代码：requestData = () => {    fetch(url).then(res => {        console.log('started fetch');return res.json()    }).then(res => {        console.log(res.list);let dataBlob=res.list;this.setState({            //data: [...this.state.data, ...res],            data: dataBlob,            error: res.error || null,            laoding: false,            refreshing: false,        });    }).catch(err => {        console.log('==> fetch error', err);this.setState({ error: err, loading: false, refreshing: false});    });};renderItem = (item) => {var txt = '下标为：'+item.index+'姓名'+item.item.userName;var bgColor = item.index % 2 == 0 ? 'red' : 'blue';return <Text style={[{flex:1,height:200,backgroundColor:bgColor},styles.txt]}>{txt}</Text>}跪求！！！