我有一个React组件,在组件的渲染方法中,我有这样的东西:

render() {
    return (
        <div>
            <div>
                // removed for brevity
            </div>

           { switch(...) {} }

            <div>
                // removed for brevity
            </div>
        </div>
    );
}

Now the point is that I have two div elements, one at the top and one at the bottom, that are fixed. In the middle I want to have a switch statement, and according to a value in my state I want to render a different component. So basically, I want the two div elements to be fixed always, and just in the middle to render a different component each time. I'm using this to implement a multi-step payment procedure). Though, as is the code currently it doesn't work, as it gives me an error saying that switch is unexpected. Any ideas how to achieve what I want?


当前回答

这个答案专门用来解决@tonyfat提出的“重复”问题,关于如何使用条件表达式来处理相同的任务。


Avoiding statements here seems like more trouble than it's worth, but this script does the job as the snippet demonstrates:

// Runs tests let id = 0, flag = 0; renderByFlag(id, flag); // jobId out of range id = 1; // jobId in range while(++flag < 5){ // active flag ranges from 1 to 4 renderByFlag(id, flag); } // Defines a function that chooses what to render based on two provided values function renderByFlag(jobId, activeFlag){ jobId === 1 ? ( activeFlag === 1 ? render("A (flag = 1)") : activeFlag === 2 ? render("B (flag = 2)") : activeFlag === 3 ? render("C (flag = 3)") : pass(`flag ${activeFlag} out of range`) ) : pass(`jobId ${jobId} out of range`) } // Defines logging functions for demo purposes function render(val){ console.log(`Rendering ${val}`); } function pass(reason){ console.log(`Doing nothing (${reason})`) }

其他回答

我们可以直接使用useCallback来做到这一点

const renderContent = useCallback(() => { switch (sortState) { “一”: 返回“一”; “两个”: 返回“两个”; “三”: 返回“三”; “四”: 返回“四”; 默认值: 返回“一”; } }, [sortState]);

这将在jsx中使用

<div>排序:{renderContent()}</div>

你可以这样做。

 <div>
          { object.map((item, index) => this.getComponent(item, index)) }
 </div>

getComponent(item, index) {
    switch (item.type) {
      case '1':
        return <Comp1/>
      case '2':
        return <Comp2/>
      case '3':
        return <Comp3 />
    }
  }

你不能在渲染中有开关。放置访问一个元素的对象文字的伪切换方法并不理想,因为它会导致所有视图都要处理,并且可能导致在该状态下不存在的道具的依赖错误。

这里有一个很好的干净的方法来做到这一点,不需要每个视图提前渲染:

render () {
  const viewState = this.getViewState();

  return (
    <div>
      {viewState === ViewState.NO_RESULTS && this.renderNoResults()}
      {viewState === ViewState.LIST_RESULTS && this.renderResults()}
      {viewState === ViewState.SUCCESS_DONE && this.renderCompleted()}
    </div>
  )

如果视图状态的条件不只基于一个简单的属性——比如每行有多个条件,那么枚举和getViewState函数封装条件是分离条件逻辑和清理呈现的好方法。

我正在使用这个帮助器,它允许我在JSX中有开关语句

// in helpers folder const switchTrue = (object) => { const { default: defaultValue, ...rest } = object; const obj = { default: defaultValue, ...rest }; const result = Object.keys(obj).reduce((acc, cur) => { return { ...acc, [cur === 'default' ? 'true' : cur]: obj[cur], }; }, {}); return result['true']; }; const Sample = () => { const isDataLoading = false; return ( <div> { switchTrue({ [`${isDataLoading}`]: <div>Loading</div>, [`${!isDataLoading}`]: <div>Data Ready</div>, default: <div>Default</div>, }) } </div> ) } ReactDOM.render( <Sample/>, document.getElementById("react") ); <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script> <div id="react"></div>

  const [route, setRoute] = useState(INITIAL_ROUTE)

  return (
    <RouteContext.Provider value={{ route, setRoute }}>
      {(() => {
        switch (route) {
          case Route.Home:
            return <PopupHomePage />
          case Route.App:
            return <PopupAppPage />
          default:
            return null
        }
      })()}
    </RouteContext.Provider>