如何在React组件中使用switch语句?

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

我真的很喜欢https://stackoverflow.com/a/60313570/770134中的建议，所以我把它改成了Typescript

import React, { FunctionComponent } from 'react'
import { Optional } from "typescript-optional";
const { ofNullable } = Optional

interface SwitchProps {
  test: string
  defaultComponent: JSX.Element
}

export const Switch: FunctionComponent<SwitchProps> = (props) => {
  return ofNullable(props.children)
    .map((children) => {
      return ofNullable((children as JSX.Element[]).find((child) => child.props['value'] === props.test))
        .orElse(props.defaultComponent)
    })
    .orElseThrow(() => new Error('Children are required for a switch component'))
}

const Foo = ({ value = "foo" }) => <div>foo</div>;
const Bar = ({ value = "bar" }) => <div>bar</div>;
const value = "foo";
const SwitchExample = <Switch test={value} defaultComponent={<div />}>
  <Foo />
  <Bar />
</Switch>;

2020-09-11 18:11:39

其他回答

这个助手应该可以做到这一点。使用示例:

{componentSwitch(3, (switcher => switcher
    .case(1, () =>
        <p>It is one</p>
    )
    .case(2, () =>
        <p>It is two</p>
    )
    .default(() =>
        <p>It is something different</p>
    )
))}

助手:

interface SwitchCases<T> {
    case: (value: T, result: () => React.ReactNode) => SwitchCases<T>;
    default: (result: () => React.ReactNode) => SwitchCases<T>;
}

export function componentSwitch<T>(value: T, cases: (cases: SwitchCases<T>) => void) {

    var possibleCases: { value: T, result: () => React.ReactNode }[] = [];
    var defaultResult: (() => React.ReactNode) | null = null;

    var getSwitchCases: () => SwitchCases<T> = () => ({
        case: (value: T, result: () => React.ReactNode) => {
            possibleCases.push({ value: value, result });

            return getSwitchCases();
        },
        default: (result: () => React.ReactNode) => {
            defaultResult = result;

            return getSwitchCases();
        },
    })
    
    // getSwitchCases is recursive and will add all possible cases to the possibleCases array and sets defaultResult.
    cases(getSwitchCases());

    // Check if one of the cases is met
    for(const possibleCase of possibleCases) {
        if (possibleCase.value === value) {
            return possibleCase.result();
        }
    }

    // Check if the default case is defined
    if (defaultResult) {
        // Typescript wrongly assumes that defaultResult is always null.
        var fixedDefaultResult = defaultResult as (() => React.ReactNode);

        return fixedDefaultResult();
    }

    // None of the cases were met and default was not defined.
    return undefined;
}

2022-01-22 14:16:40

这是因为switch语句是一个语句，但这里javascript需要一个表达式。

虽然，不建议在呈现方法中使用switch语句，但你可以使用自调用函数来实现这一点:

render() {
    // Don't forget to return a value in a switch statement
    return (
        <div>
            {(() => {
                switch(...) {}
            })()}
        </div>
    );
}

2017-10-05 19:02:10

Lenkan的回答是一个很好的解决方案。

<div>
  {{ beep: <div>Beep</div>,
     boop: <div>Boop</div>
  }[greeting]}
</div>

如果需要一个默认值，那么您甚至可以这样做

<div>
  {{ beep: <div>Beep</div>,
     boop: <div>Boop</div>
  }[greeting] || <div>Hello world</div>}
</div>

或者，如果这对你来说不太好，那么你可以做一些

<div>
  { 
    rswitch(greeting, {
      beep: <div>Beep</div>,
      boop: <div>Boop</div>,
      default: <div>Hello world</div>
    }) 
  }
</div>

with

function rswitch (param, cases) {
  if (cases[param]) {
    return cases[param]
  } else {
    return cases.default
  }
}

2019-01-04 19:04:06

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>

2022-10-25 19:49:10

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。

2019-04-09 18:45:28

如何在React组件中使用switch语句?

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