title: React-navigation custom OnClick
body: <p>I'm trying to make a button in the middle of the screen that will navigate user when clicked and i'm using react-navigation library. How do i do it without stackNavigator, HeaderNavigator or DrawerNavigator ?       </p>
  
  <pre><code>import React, { Component } from 'react';
  import { Text } from 'react-native';
  import { Button } from 'react-native-elements';
  
      export default class LoginButton extends Component {
        onPressButton() {
          console.log('pressed');
        }
        render() {
          return (
                &lt;Button
                title='LOG IN'
                buttonStyle={styles.loginButton}
                onPress= ## how do i do it?
                /&gt;
          );
        }
      }
  
      const styles = {
  
        loginButton: {
          width: 290,
          height: 50,
          backgroundColor: '#A91515',
          alignItems: 'center',
          borderRadius: 4,
          marginTop: 35,
          marginLeft: 49,
          justifyContent: 'space-around'
        }
      };
  </code></pre>