在元素列表中未定义对元素的React Native ref

Question

I am trying to get a ref to an element whilst rendering a flatlist but the ref is coming back as undefined. See relevant code below:

Constructor:

constructor(props) {
    super(props);

    this.modalRef = createRef();
}

RenderItem:

_renderItem = ({ item }, context) => {
    const modalRef = context.modalRef.current; // Why is context.modalRef.current null?
    let onPress = () => alert("Something went wrong...");

    return (
        <View style={styles.item}>
            <ListItemCard
                id={item.id}
                value="Some value.."
                onPress={onPress()}
            />
        </View>
    );
};

Within Render function:

Modal on screen:

    <Modal
    ref={this.modalRef}
    text="Some text.."
    onPressClose={() =>
        this.modalRef.current.close()
    }
/>

Flatlist:

  <FlatList
    data={data}
    renderItem={item => this._renderItem(item, this)}
    keyExtractor={(item, index) => index.toString()}
/>

Answer 1

modalRef.current is null because the reference is assigned on mount of the Modal component. I assume that the component is not mounted at the time the _renderItems function is called.

I recommend that you use the ref inside a function that does not render a component, for example an event handler. There the ref variable should have a reference to the component.