react-第六章-useContext

useContext

可多个组件共享某些状态

使用useContext，就不需用在使用 props 一层一层传递。

用法：

使用 createContext.Provider 来包裹需要共享数据的组件，并通过 value 属性传递数据

import React, { useContext, useState } from 'react';
// 创建上下文
const ThemeContext = React.createContext<ThemeContextType>({} as ThemeContextType);
// 定义上下文类型
interface ThemeContextType {
   theme: string;
   setTheme: (theme: string) => void;
}
const Child = () => {
    // 获取上下文
   const themeContext = useContext(ThemeContext);
   const styles = {
      backgroundColor: themeContext.theme === 'light' ? 'white' : 'black',
      border: '1px solid red',
      width: 100 + 'px',
      height: 100 + 'px',
      color: themeContext.theme === 'light' ? 'black' : 'white'
   }
   return <div>
      <div style={styles}>
         child
      </div>
   </div>
}

const Parent = () => {
    // 获取上下文
   const themeContext = useContext(ThemeContext);
   const styles = {
      backgroundColor: themeContext.theme === 'light' ? 'white' : 'black',
      border: '1px solid red',
      width: 100 + 'px',
      height: 100 + 'px',
      color: themeContext.theme === 'light' ? 'black' : 'white'
   }
   return <div>
      <div style={styles}>
         Parent
      </div>
      <Child />
   </div>
}

function App() {
   const [theme, setTheme] = useState('light');
   return (
      <div>
         <button onClick={() => setTheme(theme === 'light' ? 'dark' : 'light')}>切换主题</button>
         <ThemeContext.Provider value={{ theme, setTheme }}>
            <Parent />
         </ThemeContext.Provider>
      </div >
   );
}

export default App;