Tcomb-form-native: Add es6 support for getValue()

[chauthai]

Hi,

please add es6 class support for the getValue().
When I define a new component as a class, I can't use the this.ref.form.getValue() function to get
the values.

Example class:

class CreateEvent extends React.Component {

  componentDidMount() {
        //this.refs.form.getComponent('menu').refs.input.focus();
    }

  onPress() {
     console.log('Save button pressed.')
    // call getValue() to get the values of the form
     var value = this.refs.form.getValue();
     if (value) { // if validation fails, value will be null
       console.log(value); // value here is an instance of Person
     }
  }

  render() {
    return (
      <ScrollView
        horizontal={false}
        contentInset={{top: -50}}
        style={[Styles.scrollView, Styles.horizontalScrollView]}>
        <View style={Styles.container}>
          <Form
            ref="form"
            type={Person}
            options={options}
          />
          <TouchableHighlight style={Styles.button} onPress={this.onPress} underlayColor='#99d9f4'>
            <Text style={Styles.buttonText}>Save</Text>
          </TouchableHighlight>
        </View>
      </ScrollView>
    );
    }
}

Error:

javascript Error: Cannot read property 'form' of undefined stack: Object.CreateEvent.onPress index.ios.bundle:55308 React.createClass.touchableHandlePress index.ios.bundle:34825 TouchableMixin._performSideEffectsForTransition index.ios.bundle:33004 TouchableMixin._receiveSignal index.ios.bundle:32928 TouchableMixin.touchableHandleResponderRelease index.ios.bundle:32731 executeDispatch index.ios.bundle:12786 forEachEventDispatch index.ios.bundle:12774 Object.executeDispatchesInOrder index.ios.bundle:12795 executeDispatchesAndRelease index.ios.bundle:12174 URL: undefined line: undefined message: Cannot read property 'form' of undefined```

[gcanti]

<TouchableHighlight style={Styles.button} onPress={this.onPress.bind(this)} underlayColor='#99d9f4'>

[gcanti]

bind(this) is missing

[chauthai]

Ok, thanks!
Maybe it's worth a note in the docs for noobs like me ;-)

[buncis]

make it as arrow function fix the problems

  onPress = () => {
     console.log('Save button pressed.')
    // call getValue() to get the values of the form
     var value = this.refs.form.getValue();
     if (value) { // if validation fails, value will be null
       console.log(value); // value here is an instance of Person
     }
  }