DefaultTabBar.js

'use strict';

var React = require('react-native');
var {
  Dimensions,
  StyleSheet,
  Text,
  TouchableOpacity,
  View,
  Animated,
} = React;

var deviceWidth = Dimensions.get('window').width;

var styles = StyleSheet.create({
  tab: {
    flex: 1,
    alignItems: 'center',
    justifyContent: 'center',
    paddingBottom: 10,
  },

  tabs: {
    height: 50,
    flexDirection: 'row',
    justifyContent: 'space-around',
    marginTop: 20,
    borderWidth: 1,
    borderTopWidth: 0,
    borderLeftWidth: 0,
    borderRightWidth: 0,
    borderBottomColor: '#ccc',
  },
});

var DefaultTabBar = React.createClass({
  propTypes: {
    goToPage: React.PropTypes.func,
    activeTab: React.PropTypes.number,
    tabs: React.PropTypes.array
  },

  renderTabOption(name, page) {
    var isTabActive = this.props.activeTab === page;

    return (
      <TouchableOpacity style={[styles.tab]} key={name} onPress={() => this.props.goToPage(page)}>
        <View>
          <Text style={{color: isTabActive ? 'navy' : 'black', fontWeight: isTabActive ? 'bold' : 'normal'}}>{name}</Text>
        </View>
      </TouchableOpacity>
    );
  },

  render() {
    var numberOfTabs = this.props.tabs.length;
    var tabUnderlineStyle = {
      position: 'absolute',
      width: deviceWidth / numberOfTabs,
      height: 4,
      backgroundColor: 'navy',
      bottom: 0,
    };

    var left = this.props.scrollValue.interpolate({
      inputRange: [0, 1], outputRange: [0, deviceWidth / numberOfTabs]
    });

    return (
      <View style={styles.tabs}>
        {this.props.tabs.map((tab, i) => this.renderTabOption(tab, i))}
        <Animated.View style={[tabUnderlineStyle, {left}]} />
      </View>
    );
  },
});

module.exports = DefaultTabBar;