title: React Native: this.setState is not a function
body: <p>I see a number of questions on here relating to this same issue, but it seems none match the issue I'm having, and are a bit more complex.</p>
  
  <p>I am in the process of learning ReactJS and React Native. I'm in the midst of reading and following the code examples from "Learning React Native" book here: <a href="https://github.com/bonniee/learning-react-native" rel="noreferrer">https://github.com/bonniee/learning-react-native</a></p>
  
  <p>For some reason, calling this.setState in the code below when the handleTextChange function is called, causes the "this.SetState is not a function." error. My question is why? Unlike other questions about this same issue, I don't believe my call to this.stateState is buried in a callback function or if statement. Why is it undefined?</p>
  
  <p>Here is my code:</p>
  
  <pre><code>class WeatherProject extends Component {
    constructor(props) {
      super(props);
      this.state = {
        zip: "",
        forecast: null
      };
    }
  
    _handleTextChange(event) {
      this.setState({zip: event.nativeEvent.text});
    }
  
      render() {
      return (
        &lt;View style={styles.container}&gt;
        &lt;Text style={styles.welcome}&gt;
        You input {this.state.zip}.
        &lt;/Text&gt;
        &lt;TextInput
        style={styles.input}
        onSubmitEditing={this._handleTextChange}/&gt;
        &lt;/View&gt;
      );
    }
  }
  </code></pre>