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

我将接受的答案转换为箭头功能组件解决方案，看到James提供了类似的答案，可以得到未定义的错误。这就是解决方案:

  const renderSwitch = (param) => {
    switch (param) {
      case "foo":
        return "bar";
      default:
        return "foo";
    }
  };

  return (
    <div>
      <div></div>

      {renderSwitch(param)}

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

2021-03-16 05:40:58

其他回答

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

如何:

mySwitchFunction = (param) => {
   switch (param) {
      case 'A':
         return ([
            <div />,
         ]);
      // etc...
   }
}
render() {
    return (
       <div>
          <div>
               // removed for brevity
          </div>

          { this.mySwitchFunction(param) }

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

2017-10-05 19:02:32

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

一种在渲染块中使用条件操作符表示一种开关的方法:

{(someVar === 1 &&
    <SomeContent/>)
|| (someVar === 2 &&
    <SomeOtherContent />)
|| (this.props.someProp === "something" &&
    <YetSomeOtherContent />)
|| (this.props.someProp === "foo" && this.props.someOtherProp === "bar" &&
    <OtherContentAgain />)
||
    <SomeDefaultContent />
}

应该确保条件严格返回布尔值。

2018-08-07 21:09:29

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

如何在React组件中使用switch语句?

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