App.js

<>
     <Router>
       <Scene key = 'root'>
       <Tabs
        key="tabBar"
        tabBarComponent={CustomTabBar}
        activeTintColor = 'red'
        hideNavBar
>
        <Scene key="tab1" component={()=><View></View>} title="Tab11"/>
        <Scene key="tab2" component={()=><View></View>} title="Tab12"/>
        </Tabs>
       </Scene>
     </Router>
    </>

CustomTabBar.js

import React from 'react';
import { Text, View, TouchableOpacity } from 'react-native';
import { Actions } from 'react-native-router-flux';

export default class CustomTabBar extends React.Component {
  render() {
    const { state } = this.props.navigation;
    const activeTabIndex = state.index;
    return (
           <View style={{flexDirection:'row',justifyContent:"space-around",height:50,alignItems:'center'}}>
        {
          state.routes.map((element,index) => (
            <TouchableOpacity key={element.key} onPress={() => Actions[element.key]()} >
              <Text style = {{color:index == activeTabIndex ? this.props.activeTintColor : this.props.inactiveTintColor}}>{element.params.title}</Text>
           </TouchableOpacity>
          ))
        }
      </View>
     
    );
  }
}

请问为什么会报element.params.title是undefined的错误？