ReactNative中通过setInterval改变State时的参数问题

Question

Blink是自定义的组件，通过1秒的间隔改变state属性showText值来设置Blink内容的显示，问题是下面代码的preState ，为什么可以直接调用，这个自定义的state名为什么可以直接作为参数来setState。

class Blink extends Component {
    constructor(props) {
super(props);
this.state = { showText: false };

setInterval(() => {
  this.setState(preState => {
    return { showText: !preState.showText };
  });
}, 1000);

** 下面是完整代码**

import React, { Component } from 'react';
import {
    AppRegistry,
    StyleSheet,
    Text,
    View
} from 'react-native';

class Blink extends Component {
    constructor(props) {
super(props);
this.state = { showText: false };

setInterval(() => {
  this.setState(preState => {
    return { showText: !preState.showText };
  });
}, 1000);

    }
    render() {
//三目运算符根据showText的状态来设置显示数据
let display = this.state.showText ? this.props.text : '';
return (
  <Text>{display}</Text>
)
    }

}

class Test13 extends Component {
    render() {
return (
  <View>
    <Blink text='I am the Blink,which is defined by yourself' />
    <Blink text='I am the Blink,which is the system component' />
    <Blink text='I am the Blink,view is the parent Component' />
  </View>
);
    }
}
 AppRegistry.registerComponent('Test13', () => Test13);