反应不识别参数？

Question

所以在 React 中，我有一个 App 组件正在渲染多个子组件，如下所示：

应用程序

render() {
    return (
      //JSX inside
      <BrowserRouter>
        <div>
          <Header />
          <Switch>
            <Route exact path="/" component={Courses} />
            <Route exact path="/courses/create"  component={() => <CreateCourse email={this.state.emailAddress} pass={this.state.password} />} />
            <Route exact path="/courses/:id/update" component={() => <UpdateCourse email={this.state.emailAddress} pass={this.state.password} />} />
            <Route exact path="/courses/:id" component={() => <CourseDetail email={this.state.emailAddress} pass={this.state.password} />} />
            <Route exact path="/signin" component={ () => <UserSignIn signIn={this.signIn}/>} /> {/*pass in the signIn() in a prop called signIn to the UserSignIn component*/}
            <Route exact path="/signup" component={UserSignUp} />
            {/* <Route exact path="/signout" component={UserSignOut} /> */}
          </Switch>
        </div>
      </BrowserRouter>
    );
  }

在这个组件中我有参数，所以我可以通过它的 id 查看课程：

课程详情

componentDidMount() {
    const {match: { params }} = this.props; //I used a code snippet from this video https://scotch.io/courses/using-react-router-4/route-params
    //fetch data from API
    axios
      .get(`http://localhost:5000/api/courses/${params.id}`)
      .then(results => {
        //results param came back as data from api
        this.setState({
          //set state by setting the courses array to hold the data that came from results
          course: results.data,
          user: results.data.user
        });
        //console.log(results); //By console logging I was able to see that I am getting each individual course's info in the data object
      });
  }

  //this method will be for deleting a course
  handleDelete() {
    const { match: { params }, history } = this.props;

    axios.delete(`http://localhost:5000/api/courses/${params.id}`, {
    auth: {
      username: this.props.email,
      password: this.props.pass
   }
  }).then(() => {
      history.push("/"); //I used the history object and have it push to the homepage, that way every time I delete a course I am redirected to (/) afterwards
    });
  }

当我尝试导航到使用参数的 CourseDetail 组件时遇到的错误是：

有人可以帮忙吗？

Answer 1

你需要像这样传递道具read here

component={props => <CourseDetail {...props} email={this.state.emailAddress} pass={this.state.password} />} />

传递给 courseDetails 组件的道具没有任何道具名称 match 并且在您的 componentDidMount 中您正在这样做

const {match: { params }} = this.props;

此处匹配未定义，因此您可以访问 params

看这个例子就明白了

let a = {a:{b:1}}

let {x:{b,}} = a

以上代码同下

"use strict";

var a = {
  a: {
    b: 1
  }
};
var b = a.x.b;

所以最终在这里，如果在解构过程中，如果你没有匹配作为你试图访问的参数

(this.props.match).params
         |
         |__________ This is undefined  you end up `undefined.params`

Answer 2

当你写这篇文章时

常量{匹配：{参数}}=this.props；

这意味着您希望道具具有如下匹配属性：

params = this.props.match.params;

这就是您收到指定错误的原因。

如果你想分配一个变量，道具使用这个

const params = props;

注意：[如果你用方括号括起一个变量 const {match} = props; 这意味着你期望在 props 中进行键匹配。

Answer 3

Match 未定义，因为您没有将其作为道具传递给组件。

这样做

<Route exact path="/courses/:id/update" component={(routeProps) => <UpdateCourse email={this.state.emailAddress} pass={this.state.password} routeProps = {routeProps} />} />

然后您可以通过以下方式获得匹配属性 routeProps.

const {match} = this.routeProps;

或者简单地使用 属性扩展符号 它将 routeProps 中的属性作为组件中的离散属性展开。

示例，

<Route exact path="/courses/:id/update" component={(routeProps) => <UpdateCourse email={this.state.emailAddress} pass={this.state.password} {...routeProps} />} />

这相当于写-

<Route exact path="/courses/:id/update" component={(routeProps) => <UpdateCourse email={this.state.emailAddress} pass={this.state.password} Match = {this.routeProps.Match} Location = {this.routeProps.Location}/>} History = {this.routeProps.History />

反应不识别参数？

react is not recognizing params?

javascript

reactjs

react-router

react-router-dom