反应原生createMaterialTopTabNavigator，用图像替换文本

import { createMaterialTopTabNavigator } from 'react-navigation-tabs';
import { Image } from 'react-native';

const TabNavigator = createMaterialTopTabNavigator(
  {
    Screen1: {
      screen: Screen1,
      navigationOptions: {
        tabBarIcon: ({ focused }) => (
          <Image
            source={focused ? require('image1-active.png') : require('image1-inactive.png')}
            style={{ width: 20, height: 20 }}
          />
        ),
      },
    },
    Screen2: {
      screen: Screen2,
      navigationOptions: {
        tabBarIcon: ({ focused }) => (
          <Image
            source={focused ? require('image2-active.png') : require('image2-inactive.png')}
            style={{ width: 20, height: 20 }}
          />
        ),
      },
    },
  },
  {
    tabBarOptions: {
      showIcon: true,
      showLabel: false,
    },
  }
);

export default TabNavigator;