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static contextType的使用

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司徒正美 edited this page Dec 20, 2018 · 1 revision 
<!DOCTYPE html>
<html>

<head>
	<meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
<!---
	<script src="https://cdn.bootcss.com/react/16.6.3/umd/react.development.js"></script>
  <script src="https://cdn.bootcss.com/react-dom/16.6.3/umd/react-dom.development.js"></script>
-->
 <script src="./dist/React.js"></script>

	<script type='text/javascript' src="./lib/babel.js"></script>

</head>

<body>

	<div id='root' class="root">

	</div>
	<script type='text/babel'>
        
        var container = document.getElementById('root');
          var div = container;
          if (!window.ReactDOM) {
              window.ReactDOM = React;
          }
          var expect = function(a) {
              return {
                  toBe: function(b) {
                      console.log(a, 'vs', b, a === b);
                  },
                  toEqual(b) {
                      console.log(a, 'vs', b, a + '' === b + '');
                  },
                  toThrow(){
                      try{
                          a()
                      }catch(e){
                          console.log(e,"catch")
                      }
                  }
              };
		 };
  const themes = {
  green: {
    foreground: '#000000',
    background: 'green',
  },
  red: {
    foreground: '#ffffff',
    background: 'red',
  },
};

const ThemeContext = React.createContext(
  themes.red // default value
);
class ThemedButton extends React.Component {
  render() {
    let props = this.props;
    let theme = this.context;
   console.log("ThemedButton", props, theme)
    return (
      <button
        {...props}
        style={{backgroundColor: theme.background}}
      />
    );
  }
}
ThemedButton.contextType = ThemeContext;

function Toolbar(props) {
  return (
    <ThemedButton onClick={props.changeTheme}>
      Change Theme
    </ThemedButton>
  );
}

class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      theme: themes.green,
    };
    console.log("变色")
    this.toggleTheme = () => {
      console.log(this.state.theme, '1111')
      this.setState(state => ({
        theme:
          state.theme === themes.red
            ? themes.green
            : themes.red,
      }));
    };
  }

 render() {
    // The ThemedButton button inside the ThemeProvider
    // uses the theme from state while the one outside uses
    // the default red theme
    return (
      <div>
        <ThemeContext.Provider value={this.state.theme}>
          <Toolbar changeTheme={this.toggleTheme} />
        </ThemeContext.Provider>
        <section>
          <ThemedButton>下面的</ThemedButton>
        </section>
      </div>
    );
  }
}
ReactDOM.render(<App />, container)
	
    </script>


</html>

``html

<script type='text/javascript' src="./dist/React.js"></script> <script type='text/javascript' src="./test/react.development.js"></script> <script type='text/javascript' src="./test/react-dom.development.js"></script> 
<script type='text/javascript' src="./lib/babel.js"></script>

    <pre>应该等于
       
      
    </pre>
    <h1 id='root' class="root">

    </h1>
    <script type='text/babel'>
       var container = document.getElementById("example")
        var div = container
        var PropTypes = React.PropTypes
        if(!window.ReactDOM){
          window.ReactDOM = React
        }
        var expect = function(a) {
            return {
                toBe: function(b) {
                    console.log(a,"vs", b, a === b)
                },
                toEqual(b){
                    console.log(a,"vs", b, a +""=== b+"")
                },
                toThrow(b){
                    try{
                        a()
                    }catch(e){
                        console.log(e,"vs", b, e.message +""=== b+"")
                    }
                }
            }
        }

        const Hello = ({ name }) => <h1>Hello {name}!</h1>;
        
        class ShowMyError extends React.Component {
          constructor(props) {
            super(props);
            this.state = { error: false };
          }
        
          componentDidCatch(error, info) {
              console.log(error, info)
            this.setState({ error, info });
          }
        
          render() {
            if (this.state.error) {
              return (
                <div>
                  <h1>
                    Error AGAIN: {this.state.error.toString()}
                  </h1>
                  {this.state.info &&
                    this.state.info.componentStack.split("\n").map(i => {
                      return (
                        <div key={i}>
                          {i}
                        </div>
                      );
                    })}
                </div>
              );
            }
            return this.props.children;
          }
        }
        
        class Broken extends React.Component {
          constructor(props) {
            super(props);
            this.state = { throw: false, count: 0 };
          }
        
          render() {
            if (this.state.throw) {
              throw new Error("YOLO");
            }
        
            return (
              <div>
                <button
                  onClick={e => {
                    this.setState({ throw: true });
                  }}
                >
                  button will render error.
                </button>
        
                <button onClick={e => {
                  this.setState(({ count }) => ({
                    count: count + 1
                  }));
                }}>button will not throw</button>
        
                <div>
                  {"All good here. Count: "}{this.state.count}
                </div>
              </div>
            );
          }
        }
        
        class App extends React.Component {
          render() {
            const styles = {
              fontFamily: "sans-serif",
              textAlign: "center"
            };
            return (
              <div style={styles}>
                <Hello name="ShowMyError" />
                <h2>
                  Start clicking to see some {"\u2728"}magic{"\u2728"}
                </h2>
                <ShowMyError>
                  <Broken />
                </ShowMyError>
              </div>
            );
          }
        }
        
        ReactDOM.render(<App />, document.getElementById("root"));
</script> ```
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