Cannot display array in React Native

Question

When i press the <TouchableOpacity> Button, i want the value 'abc' to be appended to the array selectedTags and then <Text> {this.list()} </Text> will print out my array.
But now when i press the Button, nothing display out.

Can anybody know what is the problem with my code?

export default class App extends Component {
      constructor(props) {
        super(props);
        this.state = {
          selectedTags: []
        }
  }

  list() {
  return this.state.selectedTags.map(function(tags, i){
    return(
      <View key={i}>
        <Text>{tags.name}</Text>
      </View>
    );
  });
}

  render() {
    return (
      <View style={styles.container}>
        <TouchableOpacity  onPress={() => this.state.selectedTags.push('abc')} key = {1} style={styles.buttonContainer}>
              <Text style={styles.buttonText}> Button </Text>
         </TouchableOpacity>

          <Text> {this.list()} </Text>
      </View>
    );
  }
}

Apolo · Accepted Answer · 2017-11-01 12:55:38Z

1

This is because you never call setState, which would trigger re-render of your component.

instead of using:

onPress={() => this.state.selectedTags.push('abc')}

try:

onPress={() => this.setState({selectedTags: this.state.selectedTags.concat('abc')})}

answered Nov 1, 2017 at 12:55

Apolo

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2 Comments

wein Over a year ago

why use concat instead of push??

Apolo Over a year ago

because push change the array but does not return anything. concat does not change the array but return a new array with the value provided added at the end of the new array. So in order to assign the new selectedTags attribute I need to use concat

Prince · Accepted Answer · 2017-11-01 14:19:46Z

1

The function list only push data in array but does not rerender the view, todo so you have to use setState or forceUpdate.

You can implement the onpress function like this.

onPress = () =>{
  this.state.selectedTags.push("abc");
  this.setState({selectedTags : this.state.selectedTags});
}

answered Nov 1, 2017 at 14:19

Prince

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