问打印来自变量react-native的值

EN

`
var str="";

class WeatherProject extends Component{

  constructor (props) {
    super(props);
    this.state={
        From:'',
        To:''
    }

  }

 changeText=(From)=>{
   this.setState({From})

 }
 onPress = ()=>{
  str= this.state.From
 }
  render(){
return (
<View>
    <TextInput placeholder="From" id="from" style={styles.fromField} onChangeText={this.changeText} /> 
    <Button
      title={"Press"}
      color="#f194ff"
      onPress={this.onPress}
      ></Button>

      <Text>{str}</Text> //Here i need the output via variable str
      </View>

);
}
}

export default WeatherProject