TypeError:undefined不是对象(计算this.getActiveTab().barColor)

TypeError:undefined不是对象(正在计算)

import React, { Component } from 'react';
import { StyleSheet, Text, View } from 'react-native';
import home from "../../../assets/home.png";
import form from "../../../assets/home.png";
import contact from "../../../assets/home.png";
import BottomNavigation, {
  FullTab, Tab
} from 'react-native-material-bottom-navigation';

import Icon from 'react-native-vector-icons/MaterialIcons';
export default class BottomView extends Component {
  constructor(props){
    super(props);
    this.state = { activeTab: 0 };
  }

  handleTabChange = (newTabIndex, oldTabIndex) => {
        this.setState({ activeTab: newTabIndex });
        if (newTabIndex === oldTabIndex) {
          null;
        }
        if (this.state.activeTab === 0) {
        } else if (this.state.activeTab === 1) {
        } else {
        }
    }

  render(){
    return(
      <View style={styles.container}>   
                <BottomNavigation
                    activeTab={this.state.activeTab}
                    labelColor="#5c007a"
                    rippleColor="white"
                    style={{
                      height: 56,
                      elevation: 8,
                      position: 'absolute',
                      left: 0,
                      bottom: 0,
                      right: 0
                    }}
                    onTabChange={this.handleTabChange}
                >
                    <Tab 
                      barBackgroundColor="#fff"
                      label="Home"
                      icon={<Icon size={24} color="#5c007a" name="home" />}
                    />
                    <Tab 
                      barBackgroundColor="#fff"
                      label="Categories"
                      icon={<Icon size={24} color="#5c007a" name="list" />}
                    />
                    <Tab
                      barBackgroundColor="#fff"
                      label="Profile"
                      icon={<Icon size={24} color="#5c007a" name="person" />}
                    />
                </BottomNavigation>
            </View>
    )
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  }
});