title: React Native get undefined is not an object error
body: <p>I am new to react native.</p>
  
  <p>When I ran my codes on Android emulator I got this error: </p>
  
  <blockquote>
    <blockquote>
      <p>undefined is not an object, evaluating ChangeTextHandler.bind(this).</p>
    </blockquote>
  </blockquote>
  
  <p>Please help on this. Thanks. </p>
  
  <p>Here are my codes. Did I miss anything?</p>
  
  <pre><code>import React, {Component} from 'react';
  import {Platform, StyleSheet, Text, TextInput, View} from 'react-native';
  
  const instructions = Platform.select({
    ios: 'Press Cmd+R to reload,\n' + 'Cmd+D or shake for dev menu',
    android:
      'Double tap R on your keyboard to reload,\n' +
      'Shake or press menu button for dev menu',
  });
  
  // type Props = {};
  export default class App extends Component {
    constructor(){
      super()
      this.state= {
        value: "default text"
      }
      this.onChangeTextHandler = this.ChangeTextHandler.bind(this)
    }
  
  
    onChangeTextHandler(newText){
        this.setState(
          {
            value: newText
          }
        )
        }
  
  
    render() {
      return (
        &lt;View style={styles.container}&gt;
          &lt;Text style={styles.welcome}&gt;Welcome to React Native!&lt;/Text&gt;
          &lt;Text&gt;Username:  &lt;/Text&gt;
          &lt;TextInput defaultValue = "username"
            onChangeText={this.onChangeTextHandler} /&gt;
          &lt;Text&gt; You are writing {this.state.value}&lt;/Text&gt;
          &lt;Text&gt;Password:  &lt;/Text&gt;
          &lt;TextInput  /&gt;
        &lt;/View&gt;
      );
    }
  }
  
  const styles = StyleSheet.create({
    container: {
      flex: 1,
      justifyContent: 'center',
      alignItems: 'center',
      backgroundColor: '#F5FCFF',
    },
    welcome: {
      fontSize: 20,
      textAlign: 'center',
      margin: 10,
    },
    instructions: {
      textAlign: 'center',
      color: '#333333',
      marginBottom: 5,
    },
  });
  </code></pre>
  
  <p>By the way I got errors "looks like most of your post is codes, please add more details". But I dont have any more to say.</p>