title: Cannot read property [PROPERTY] of undefined in this.state in React native
body: <p>I am new in React-native and I learn from Udemy videos. I follow videos but because of react-native version differences things changed.
  I have an error <code>this.state</code> that is <code>undefined</code>.</p>
  
  <blockquote>
    <p>Cannot read property 'newTodoText' of undefined</p>
  </blockquote>
  
  <p>I use <code>react-redux</code> </p>
  
  <p>this is my Main.js code</p>
  
  <pre><code>constructor(props) {
          super(props);
          this.state = {
              newTodoText: ""
          };
      }
  
  addNewTodo(){
      console.log(this.state);  // undefined &lt;------------ 
      var newTodoText = this.state.newTodoText;
      {/* var {newTodoText} = this.state; */}
      if (newTodoText &amp;&amp; newTodoText != "") {
          this.setState({
              newTodoText: ""
          })
          this.props.dispatch(addTodo(newTodoText));
      }
  }
  </code></pre>
  
  <p>and this is my <code>render()</code></p>
  
  <pre><code>&lt;TextInput  
        onChangeText={(text) =&gt; this.setState({newTodoText:text})}
        value={this.state.newTodoText}
        returnKeyType="done"
        placeholder="New ToDo"
        onSubmitEditing={this.addNewTodo}
        underlineColorAndroid="transparent"
        style={styles.input}
  &gt;
  
  &lt;/TextInput&gt;
  </code></pre>