从“平面”列表项导航到另一个屏幕

Question

I'm trying to navigate to another screen when I click on one of the items on the flat list.

The code that I have here worked for a couple of days but now it doesn't, straight away when the app loads, the EventDetailScreen is opened even before I click on any of the flat list items, then when I press the back button from the EventDetailScreen which brings me back to the EventListScreen, if I click on any of the list items nothing happens and I don't get brought to the EventDetailScreen.

I also get an error:

Warning: Cannot update during an existing state transition (such as within render or another component's constructor). Render methods should be a pure function of props and state; constructor side-effects are an anti-pattern, but can be moved to componentWillMount .

I am new to React Native so any help would be much appreciated!

I am using: "react-navigation": "^2.7.0", "react": "16.4.1", "react-native": "0.56.0",

I used this answer Navigating to each item in FlatList on SO to get it working initially.

EventListScreen.js

export default class EventListScreen extends Component {

constructor() {
    super();
    this.ref = firebase.firestore();
    this.unsubsribe = null;

    this.state = {
        eventName: '',
        eventLocation: '',
        loading: true,
        events: [],
    };
}

componentDidMount() {
    console.log('EventsListScreen1');
    this.unsubsribe = this.ref.onSnapshot(this.onCollectionUpdate)
}

componentWillUnmount() {
    this.unsubsribe();
}


openDetails = () => {
    this.props.navigation.navigate('EventDetailScreen');
};

render() {

    if (this.state.loading) {
        return null;
    }

    return (
        <Container>

            <FlatList
                data={this.state.events}
                // Get the item data by referencing as a new function to it
                renderItem={({item}) =>
                    <Event
                    openDetails={() => this.openDetails()}
                    {...item} />}
            />

            <View style={{flex: 1}}>
                <Fab
                    active={this.state.active}
                    direction="left"
                    containerStyle={{}}
                    style={{backgroundColor: '#5067FF'}}
                    position="bottomRight"
                    onPress={() => 
                    this.props.navigation.navigate('EventForm')
                    }>
                    <Icon 
                       name="ios-add"/>
                </Fab>
            </View>

        </Container>
    );
}

Event.js

export default class Event extends Component {

render() {

    return (
        <Card>
            <CardSection>
                <Text>{this.props.eventName}</Text>
            </CardSection>

            <TouchableOpacity
              onPress={this.props.openDetails()}
            >
            <CardSection>
                <Image
                    style={{
                       width: 350,
                       height: 300
                    }}
                    source={{
                       uri: this.props.imageDownloadUrl
                    }}
                />
            </CardSection>

            <CardSection>
                <Text>{this.props.eventLocation}</Text>
            </CardSection>
            </TouchableOpacity>
        </Card>
    );
}};

EventDetailScreen.js

export default class EventDetailScreen extends Component {
render() {
    /* 2. Get the param, provide a fallback value if not available */
    const { navigation } = this.props;
    const itemId = navigation.getParam('itemId', 'NO-ID');

    return (
        <View 
           style={{ 
              flex: 1,
              alignItems: 'center',
              justifyContent: 'center' 
            }}>
            <Text>Details Screen</Text>
        </View>
    );
}}

Answer 1

This is probably because of the following line in Event component.

<TouchableOpacity
    onPress={this.props.openDetails()} // <-- this line to be specific
 > ... </>

As soon as EventScreenList renders the list, the first row executes openDetails() method which switches the screen.

You can avoid this by using onPress={() => this.props.openDetails()} .

Also its a good idea to have the following in constructor or componentDidMount of EventScreenList component because both the function uses this context of the statement.

this.openDetails = this.openDetails.bind(this);
this.onCollectionUpdate = this.onCollectionUpdate.bind(this);

To check the significance of above statement, try

<TouchableOpacity
    onPress={this.props.openDetails} // <-- this line
 > ... </>

The warning message is due to navigation before state update finishes.