duda react onchange

gistfile1.txt

export default class App extends Component {
  constructor(props) {
    super(props);
    
    this.state = { 
      texto: '',
      saludo: '',
      cambio: ''
    };
    
    this.show = this.show.bind(this);
    this.changing = this.changing.bind(this);
  }
  
  show(){
    this.setState({ saludo:  `Hola ${this.state.texto}`}); 
  }
  
  changing(e){
    this.setState({
      texto: e.target.value
    })
  }
  
  render() {
    return (
      <View style={styles.container}>
        <TextInput
        style={{height: 40, width:100, borderColor: 'gray', borderWidth: 1, textAlign: 'center', marginBottom: 20}}
        value={this.state.texto}
        onChangeText={this.changing}
        />
        
        
        <Button title="Hola" color="#2f2f2f" onPress={this.show}/>
        
        <Text style={styles.paragraph}>
          {this.state.saludo.toUpperCase()}
        </Text>
      </View>
    );
  }
  
}