Conditionally style not working in react native - react-native

Question

I followed this answer to dynamically style my component.
Here is my render method :
render() {
return (
<View style={styles.container}>
<FlatList
data={this.state.images}
numColumns={2}
keyboardShouldPersistTaps={'always'}
keyboardDismissMode={'on-drag'}
keyExtractor={item => item.localIdentifier}
renderItem={({ item, index }) =>
<TouchableHighlight
underlayColor='transparent'
onPress={() => this.openImage(index)}
onLongPress={() => this.startSelection(item)}
>
<View style={[styles.albumContainer, (this.state.selectedItems.indexOf(item)>-1)?styles.selectedItem:styles.unselectedItem]}>
<Image
style={styles.albumThumbnail}
source={item.image}
/>
</View>
</TouchableHighlight>
}
/>
</View>
);
}
As you can see I am displaying image thumbnail with TouchableHighlight and FlatList. When user will press and hold on any image thumbnail I called startSelection() with particular flatlist item which then add that item to state. I used that state to set style dynamically of my image as :
<View style={[styles.albumContainer, (this.state.selectedItems.indexOf(item)>-1)?styles.selectedItem:styles.unselectedItem]}>
<Image
style={styles.albumThumbnail}
source={item.image}
/>
</View>
Here is startSelection() method :
startSelection(item) {
let temp = this.state.selectedItems;
temp.push(item);
this.setState({
selectedItems : temp
});
}
Here is my stylesheet :
const styles = StyleSheet.create({
selectedItem: {
borderWidth: 3,
borderColor: '#22aaff',
},
unselectedItem: {
borderColor: '#000000',
}
});
But when user press and hold that view, item will added to state but style is not changing.
Please help me what's going wrong here !!!

Answer 1

This can be found on FlatList docs:
This is a PureComponent which means that it will not re-render if props remain shallow-equal. Make sure that everything your renderItem function depends on is passed as a prop (e.g. extraData) that is not === after updates, otherwise your UI may not update on changes. This includes the data prop and parent component state.
So you can add extraData to your FlatList component like this:
FlatList Component:
<FlatList
data={this.state.images}
extraData={this.state} //add this!
numColumns={2}
keyboardShouldPersistTaps={'always'}
keyboardDismissMode={'on-drag'}
keyExtractor={item => item.localIdentifier}
renderItem={({ item, index }) =>
<TouchableHighlight
underlayColor='transparent'
onPress={() => this.openImage(index)}
onLongPress={() => this.startSelection(item)}
>
<View style={[styles.albumContainer, (this.state.selectedItems.indexOf(item)>-1)?styles.selectedItem:styles.unselectedItem]}>
<Image
style={styles.albumThumbnail}
source={item.image}
/>
</View>
</TouchableHighlight>
}
/>
P.S: If your component state has variables which should not re-render FlatList, you would be better of using extraData = {this.state.selectedItems}, but then you need to make sure you pass a different reference to selectedItems when you call setState on startSelection. Like this:
startSelection(item) {
let temp = [...this.state.selectedItems];
temp.push(item);
this.setState({
selectedItems : temp
});
}

Answer 2

Wrap them with extra []
style={[styles.albumContainer, [(this.state.selectedItems.indexOf(item)>-1)?styles.selectedItem:styles.unselectedItem]]}