react中父组件引用子组件的问题--2019.5.7

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
import toDoApp from './components/todoApp'

class App extends Component {
  render() {
    return (
      <div className="App">
        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
           <toDoApp />
        </header>
      </div>
    );
  }
}

export default App;

上面是源代码。没看出有什么问题。后来不断测试。发现引入组件标签第一位一定要大写

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
import ToDoApp from './components/todoApp'

class App extends Component {
  render() {
    return (
      <div className="App">
        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
           <ToDoApp />
        </header>
      </div>
    );
  }
}

export default App;