How to pass data between child and parent in react-native?

To call Parent's method from child, you can pass the reference like this.

Parent Class

<ChildClass
    onRef={ref => (this.parentReference = ref)}
    parentReference = {this.parentMethod.bind(this)}
/>

parentMethod(data) {

}

Child Class

let data = {
    id: 'xyz',
    name: 'zzz',
};

//This will call the method of parent

this.props.parentReference(data);

You need to pass from parent to child callback function, and then call it in the child.

For example:

class Parent extends React.Component {
  constructor(props){
    super(props);
    this.state = {
      show: false
    };
  }
  updateState = () => {
      this.setState({
          show: !this.state.show
      });
  }
  render() {
    return (
        <Child updateState={this.updateState} />
    );
  }
}

class Child extends React.Component {
  handleClick = () => {
      this.props.updateState();
  }
  render() {
    return (
        <button onClick={this.handleClick}>Test</button>
    );
  }
}