title: undefined is not a function (evaluating '_this2.closeDrawer()') error in react native app
body: <p>I am beginner of react native. I am using NativeBase Components for designing. When I use drawer app giving this error </p>
  
  <pre><code>undefined is not a function (evaluating '_this2.closeDrawer()')
  </code></pre>
  
  <p><strong>This is screenshot of error</strong> </p>
  
  <p><a href="https://i.stack.imgur.com/cBbdx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cBbdx.png" alt="enter image description here"></a></p>
  
  <p><strong>Drawer Code is here</strong> </p>
  
  <pre><code>import React, { Component } from 'react';
  import { Drawer } from 'native-base';
  import SideBar from './sidebar';
  import Signup from './signup';
  import { View } from 'react-native';
  
  export default class NativeDrawer extends Component {
    render() {
      closeDrawer = () =&gt; {
        this.drawer._root.close()
      };
      openDrawer = () =&gt; {
        this.drawer._root.open()
      };
      return (
        &lt;View&gt;
  
          &lt;Drawer
            ref={(ref) =&gt; { this.drawer = ref; }}
            content={&lt;SideBar navigator={this.navigator} /&gt;}
            onClose={() =&gt; this.closeDrawer()} &gt;
          &lt;/Drawer&gt;
        &lt;/View&gt;
      );
    }
  }
  </code></pre>
  
  <p><strong>SideBar code is here</strong></p>
  
  <pre><code>import React, { Component } from 'react';
  import { View, Text, StyleSheet } from 'react-native';
  
  export default class SideBar extends Component {
      render() {
  
          return (
              &lt;View style={styles.container} &gt;
                  &lt;Text&gt;
                      Hello World
                  &lt;/Text&gt;
              &lt;/View&gt;
          );
      }
  }
  
  const styles = StyleSheet.create({
      container: {
          flex: 1,
          backgroundColor: '#fff',
          alignItems: 'center',
          justifyContent: 'center',
      },
  });
  </code></pre>
  
  <p>Other NativeBase components are working but Drawer is giving an error </p>