App.js

import React, { Component } from "react";
import { Container, Header } from "semantic-ui-react";
import AddItem from "./AddItem";
class App extends Component {
  state = {
    counter: 0
  };
  handleIncrement = () => {
    this.setState({
      counter: this.state.counter + 1
    });
  };
  render() {
    return (
      <Container>
        <Header as="h1" className="centered">
          Shopping List App
        </Header>
        <button onClick={this.handleIncrement}>+</button>
        {this.state.counter}
        <AddItem />
      </Container>
    );
  }
}
export default App;