简单粗暴上代码

父组件

import React, { Component } from 'react';
import {
    Text,
    View,
} from 'react-native';
import Item from './Item'

export default class Test extends Component {
    constructor(props) {
        super(props)
        this.state = {
            mark:'初始值'
        }
    }

    fn(val){
        this.setState({
            mark:val
        });
    }

    render() {
        return (
            <View>
                <Item fn={this.fn.bind(this)}/>
                <Text>{this.state.mark}</Text>
            </View>
        )
    }
}

子组件

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

export default class Item extends Component {
    render() {
        return (
            <View>
                <Text onPress={()=>{
                    this.props.fn('子组件的值')
                }}>点击</Text>
            </View>
        )
    }
}

如果没有加bind(this)会报错-this.setState is not a function