reactjs – “undefined不是一个对象”this.state没有受到约束

代码如下.我没有看到与网站上的例子有本质上的不同,所以我无法弄清楚我做错了什么.我怎样才能解决这个问题？

'use strict';

var React = require('react-native');

var Main = React.createClass({
  getInitialState: () => {
    return { username: '',isloading: false,iserror: false };
  },handleChange: (event) => {
    this.setState({
      username: event.nativeEvent.text
    });
  },handleSubmit: (event) => {
    this.setState({
      isloading: true
    });
    console.log('Submitting... ' + this.state.username);
  },render: () => {
    return (
      <View style={styles.mainContainer}>
        <Text> Search for a Github User</Text>
        <TextInput style={styles.searchInput}
                   value={this.state.username}
                   onChange={this.handleChange.bind(this)} /> 
        <TouchableHighlight style={styles.button}
                            underlayColor='white'
                            onPress={this.handleSubmit.bind(this)} /> 
        <Text style={styles.buttonText}> SEARCH</Text>
      </View>
    );
  }
});

var { Text,View,StyleSheet,TextInput,TouchableHighlight,ActivityIndicatorIOS } = React;

var styles = StyleSheet.create({
  mainContainer: {
    flex: 1,padding: 30,marginTop: 65,flexDirection: 'column',justifyContent: 'center',backgroundColor: '#48BBEC'
  },title: {
    marginBottom: 20,fontSize: 25,textAlign: 'center',color: '#fff'
  },searchInput: {
    height: 50,padding: 4,marginRight: 5,fontSize: 23,borderWidth: 1,borderColor: 'white',borderRadius: 8,color: 'white'
  },buttonText: {
    fontSize: 18,color: '#111',alignSelf: 'center'
  },button: {
    height: 45,flexDirection: 'row',backgroundColor: 'white',marginBottom: 10,marginTop: 10,alignSelf: 'stretch',justifyContent: 'center'
  },});

module.exports = Main