this.state is undefined during onPress event in react native
<p>Hello i new in react native, my code is: </p>

<p><div class="snippet" data-lang="js" data-hide="false">
<div class="snippet-code">
<pre class="snippet-code-html lang-html prettyprint-override"><code>import React, {
  View,
  Text,
  TextInput,
  Component
} from 'react-native';

import Style from './styles/signin';
import Button from '../common/button';

export default class SignIn extends Component {
  constructor(props) {
    super(props);
    this.state = {
      email: '',
      password: ''
    };
  }

  render(){
    return(
      &lt;View style={Style.container}&gt;
        &lt;Text style={Style.label}&gt;Email&lt;/Text&gt;
        &lt;TextInput
          style={Style.input}
          onChangeText={(text) =&gt; this.setState({email: text})}
          value={this.state.email}
        /&gt;
        &lt;Text style={Style.label}&gt;Password&lt;/Text&gt;
        &lt;TextInput
          style={Style.input}
          onChangeText={(text) =&gt; this.setState({password: text})}
          value={this.state.password}
          secureTextEntry={true}
        /&gt;
        &lt;Button text={'Sign in'} onPress={this.onPress}/&gt;
      &lt;/View&gt;
    );
  }
  onPress(){
    console.log(this.state.email);
  }
}</code></pre>
</div>
</div>
</p>

<p>When i fill this form and press sign in, i have this error message: "Cannot read property 'email' of undefined". 
Thank you for the help!</p>