WARN VirtualizedList: missing keys for items, make sure to specify a key or id property on each item or provide a custom keyExtractor.
Simply do this:
<FlatList
data={[{name: 'a'}, {name: 'b'}]}
renderItem={
({item}) => <Text>{item.name}</Text>
}
keyExtractor={(item, index) => index.toString()}
/>
reference:
https://facebook.github.io/react-native/docs/flatlist.html#keyextractor