undefined is not an object (evaluating 'this.props.navigator.push')

在通过navigator 进行页面跳转的过程中  一直报 这样的错误

先看程序入口文件index.android.js

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  Text,
  TouchableHighlight,  
  Navigator,
} from 'react-native';
import Welcome from './Welcome';

 class MyProject extends Component {

  render() {
       var defaultName = 'Welcome';
     var defaultComponent = Welcome;
    return (
    
              //指定了默认的页面，也就是启动app之后会看到的第一屏，需要两个参数，name跟component
          initialRoute={{ name: defaultName, component: defaultComponent }}
          configureScene={(route) => {
            //跳转的动画
            return Navigator.SceneConfigs.FadeAndroid;
          }}
          renderScene={(route, navigator) => {
            let Component = route.component;
            if(route.component){
                return
            }
          }} />
    );
  }

}



AppRegistry.registerComponent('MyProject', () => MyProject);

再看 第一个页面 欢迎页面：Welcome.js


import React, { Component } from 'react';
import {
  Text,
  View,
  Navigator,
  TouchableHighlight
} from 'react-native';
import Login from "./Login";

export default class Welcome extends Component {
   
 
  constructor(props){
        super(props);
        this.state = {};
    }

  _onPress(){
       let navigator = this.props.navigator;
        Alert.alert('Button has been pressed!'+navigator);
        if (navigator) {
          navigator.push({
                name:'Login',
                component:Login
        });
        }
    }
  render() {
     return (
           
                  

                  

此为欢迎页面 点击进入登录页面 ); }}

红色的代替蓝色的就可以解决此问题了