React Native Element Type无效

Question

我正在尝试在React Native应用程序中呈现一些页脚选项卡，但我不确定以下代码中的内容是否为undefined。

import React, { PropTypes } from 'react'
import { Text, TabBarIOS } from 'react-native'

FooterTabs.propTypes = {
    activeFooterTab: PropTypes.string.isRequired,
    onTabSelect: PropTypes.func.isRequired,
    navigator: PropTypes.object.isRequired
}

export default function FooterTabs (props) {
    return (
        <TabBarIOS>
            <TabBarIOS.item
                title='home'
                icon={{}}
                selected={props.activeFooterTab === 'home'}
                onPress={() => {props.onTabSelect('home')}} >
                <Text>Home</Text>
            </TabBarIOS.item>
            <TabBarIOS.item
                title='camera'
                icon={{}}
                selected={props.activeFooterTab === 'camera'}
                onPress={() => {props.onTabSelect('camera')}} >
                <Text>Camera</Text>
            </TabBarIOS.item>
        </TabBarIOS>
    )
}

activeFooterTab功能

export default function activeFooterTab (state = initialState, action) {
    switch (action.type) {
        case SET_FOOTER_TAB : 
            // Returns the tab we pass in to the action creator. 
            return action.tab
        default : 
            return state
    }
}

onTabSelect功能

function mapDispatchToProps (dispatch) {
    return {
        onTabSelect: (tab) => dispatch(setFooterTab(tab))
    }
}