如何通过this.props.children将道具从父母传递给孩子？

Question

I have difficulties trying to pass props to this.props.children

I have a component MainLayout and I would like to pass props to this.props.children but his children are like that :

AppRouter.js

export default class AppRouter extends Component {

  render() {

    return (
      <HashRouter>
        <Switch>
          <MainLayout>
            <Route exact path="/" component={PubsList} />
            <Route exact path="/add-pub" component={AddPub} />
            <Route exact path="/add-pub/:id" component={AddPub} />
          </MainLayout>
        </Switch>
      </HashRouter>
    )
  }
}

MainLayout.js : I used React.Children and React.CloneElement to pass props

export default class MainLayout extends Component {

 constructor(props) {
  super(props);
  this.state = {
   foo: "foo"
  };

  render() {

    return (
      <div className="container" >
        <Menu inverted color='teal' fixed="top" style={{ margin: "0", padding: "20px", borderRadius: "0", display: "block" }}>    
          <Link to="/">
            <Header as='h2' content='PandaBar' floated="left" style={{ color: "white", margin: "0" }} />
          </Link>    
        </Menu>    

        <div className="content" style={{ marginTop: "70px", overflow: "hidden" }} >    

          {React.Children.map(this.props.children, child => {
           return React.cloneElement(child, { foo: this.state.foo })
          })}    

        </div>
      </div>
    );
  }
}

But, once my routes get the props, it appears like this:

<HashRouter>
   <Switch>
     <MainLayout>
        <Route exact path="/" component={PubsList} foo="foo"/>
        <Route exact path="/add-pub" component={AddPub} foo="foo"/>
        <Route exact path="/add-pub/:id" component={AddPub} foo="foo"/>
     </MainLayout>
    </Switch>
</HashRouter>

So, how can I pass my props foo to my component PubsList and AddPub with this configuration ?

Answer 1

Route does provide a way to pass custom props to the component, by using the render prop instead of the component prop. You pass a function in to the render prop, and that function will get called with the same props that are normally automatically passed when using component . You can then do whatever you want to with those props

An example of this (not including your mainLayout component) would look like this:

<Route render={(routeProps) => (
  <PubsList hello="world" {...routeProps} />
)}/>

So using this, you can put arbitrary props onto the components. But then how to let MainLayout dictate what those extra props are? There i think you'll need to modify MainLayout to have a render prop of its own.

render() {
  let children = null;
  if (this.props.render) {
    children = this.props.render({ foo: this.state.foo })
  }

  return (
    <div className="container" >
      <Menu inverted color='teal' fixed="top" style={{ margin: "0", padding: "20px", borderRadius: "0", display: "block" }}>    
        <Link to="/">
          <Header as='h2' content='PandaBar' floated="left" style={{ color: "white", margin: "0" }} />
        </Link>    
      </Menu>    

      <div className="content" style={{ marginTop: "70px", overflow: "hidden" }} >    
        {children}
      </div>
    </div>
  );
}

And you would use it like this:

<MainLayout render={(layoutProps) => (
  <React.Fragment>
    <Route exact path="/" render={(routeProps) => 
      <PubsList {...layoutProps} {...routeProps} />
    }/>
    <Route exact path="/add-pub" render={(routeProps) => 
      <AddPub {...layoutProps} {...routeProps} />
    }/>
    <Route exact path="/add-pub/:id" render={(routeProps) => 
      <AddPub {...layoutProps} {...routeProps} />
    }/>
  </React.Fragment>
)} />

Answer 2

In the example foo prop is passed to wrong component ( Route ).

In order to be passed to route components, route component prop should be changed instead:

const withFoo = (Comp, foo) => props => <Comp {...props} foo={foo}/>;
...

  render() {

    return (
      ...
      {React.Children.map(this.props.children, route => {
        return React.cloneElement(route, {
          component: withFoo(route.props.component, this.state.foo)
        });
      })}    
      ...
    );
  }

While the use of Route render prop as another answer suggest may be more straightforward.