import React from 'react';
    import UserAuthenticationUI from './UserAuthentication/UserAuthenticationUI';
    import UserAuthenticationRequests from './UserAuthentication/UserAuthenticationRequests';

      class App extends React.Component {
          constructor(props) {
            super(props);

            this.userAuthenticationUI = React.createRef();
            this.userAuthenticationRequests = React.createRef();
        }

componentDidMount(){
this.userAuthenticationRequests.current.testMethod(); //there i can call method without problems
}

    render(){
    return(
    <div>
    <UserAuthenticationUI ref={this.userAuthenticationUI} />
    <UserAuthenticationRequests ref={this.userAuthenticationRequests} />
    <div>
        )}
    }
export default App;

import React from "react";
 import App from '../App';
 import UserAuthenticationRequests from './UserAuthenticationRequests';

  class UserAuthenticationUI extends React.Component
{
constructor(props){
super(props);

this.app = React.createRef();
this.userAuthenticationRequests = React.createRef();
}

componentDidMount() {

this.userAuthenticationRequests.current.testMethod(); //there i can not call
}

render(){
    <App/>
<UserAuthenticationRequests ref={this.userAuthenticationRequests} />
return(
<div>

</div>
)}
}

export default UserAuthenticationUI;

TypeError: Cannot read property 'testMethod' of null

testMethod(){
     console.log("test method")
 }

   render(){
   return(<div></div>)
    }
}
export default UserAuthenticationRequests;