react-native onPress binding with an argument

Question

The desired behaviour is to pass an argument (text) to the onClick handler to console.log it but it seems that I'm doing something wrong with the syntax.

If I leave the argument out as below, it's working fine:

export default class Nav extends Component {
  componentDidMount() {
    this.props.pickNumber(3);
  }

  onPress() {
    console.log('FOOOBAAR');
  }
  render() {
    return (
      <View>
        <Text>####################</Text>
        <Text>Intro Screen</Text>
        <Text>Number: {this.props.numbers}</Text>
        <TouchableHighlight onPress={this.onPress.bind(this)}>
          <Text>Go to Foo</Text>
        </TouchableHighlight>
      </View>
    );
  }

}

However, if I want to pass an argument to the onPress handler, it complains 'Cannot read property 'bind' of undefined.

export default class Nav extends Component {
  componentDidMount() {
    this.props.pickNumber(3);
  }

  onPress(txt) {
    console.log(txt);
  }
  render() {
    return (
      <View>
        <Text>####################</Text>
        <Text>Intro Screen</Text>
        <Text>Number: {this.props.numbers}</Text>
        <TouchableHighlight onPress={this.onPress('foo').bind(this)}>
          <Text>Go to Foo</Text>
        </TouchableHighlight>
      </View>
    );
  }

}

Thanks

Addition: If I change it to:

onPress={this.onPress.bind('foo')}

it does not work either.

Answer 1

You can do the binding in the constructor by using ES6:

export default class Nav extends Component {
  constructor(props) {
    super(props);

    this.onPress = this.onPress.bind(this);
  }

and then

  onPress(txt) {
    console.log(txt);
  }

  render() {
    return (
      <View>
        <Text>####################</Text>
        <Text>Intro Screen</Text>
        <Text>Number: {this.props.numbers}</Text>
        <TouchableHighlight onPress={() => this.onPress('foo')}>
          <Text>Go to Foo</Text>
        </TouchableHighlight>
      </View>
    );
  }
}

Answer 2

You can avoid binding the function in the constructor by binding it at the onPress value and passing the argument after 'this'. You can refactor your code like so,

export default class Nav extends Component {
  componentDidMount() {
    this.props.pickNumber(3);
  }

  onPress(txt) {
    console.log(txt);  // foo
  }
  render() {
    return (
      <View>
        <Text>####################</Text>
        <Text>Intro Screen</Text>
        <Text>Number: {this.props.numbers}</Text>
        <TouchableHighlight onPress={this.onPress.bind(this,'foo')}>
          <Text>Go to Foo</Text>
        </TouchableHighlight>
      </View>
    );
  }

}

The first argument is 'this' and any other arguments can be supplied after that which will be received in the same order.

Update : Can do this using closures too.

export default class Nav extends Component {
  componentDidMount() {
    this.props.pickNumber(3);
  }

  onPress = (this, txt) => () => {
    console.log(txt);  // foo
  }

  render() {
    return (
      <View>
        <Text>####################</Text>
        <Text>Intro Screen</Text>
        <Text>Number: {this.props.numbers}</Text>
        <TouchableHighlight onPress={this.onPress(this,'foo')}>
          <Text>Go to Foo</Text>
        </TouchableHighlight>
      </View>
    );
  }

}

Answer 3

You can solve it with fat arrows too:

export default class Nav extends Component {

  handlePress = (text) => {
    console.log(text);
  }

  render() {
    return (
      <View>
        <Text>####################</Text>
        <Text>Intro Screen</Text>
        <Text>Number: {this.props.numbers}</Text>
        <TouchableHighlight onPress={() => this.handlePress('weeeeee')}>
          <Text>Go to Foo</Text>
      </TouchableHighlight>
    </View>
    );
  }
}