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javascript - 三元运算符 - React 的条件渲染中是否存在可能的错误？

问题描述

目前，我正在使用 Node.js 和 React 进行开发，遇到了一个奇怪的问题，我不确定我是否遗漏了某些东西，或者它是否是 React 方面的错误。

我想要做的是使用三元运算符来呈现条件 HTML，如下所示：

...
{
  missingTradingSystemNameError
  ?
    <div>
      ...
    </div>
  :
    duplicateTradingSystemNameError
    ?
      <div>
        ...
      </div>
    :
      null
}
...

这两个三元运算符条件都是我的 JSX.Element 函数中的状态变量。但是，这样做会导致以下形式的多个错误：

错误：

React Hook "React.useEffect" is called conditionally. React Hooks must be called in the exact same order in every component render

有趣的是，如果我添加第三个（无用的）嵌套条件代替null，那么一切都按预期工作：

...
{
  missingTradingSystemNameError
  ?
    <div>
      ...
    </div>
  :
    duplicateTradingSystemNameError
    ?
      <div>
        ...
      </div>
    :
      <<condition3>>
      ?
        null
      :
        null
}
...

condition3是第三个有状态变量，但正如您所见，附加条件什么也不做，因此应该可以省略它。这是一个 React 错误还是我在这里遗漏了一些重要的东西？

（PS：请原谅我的代码不寻常的缩进，但对我来说，这是目前更复杂的 JSX 代码块最易读的解决方案）

编辑1：

为了提供一些进一步要求的细节，这里是我简化的 useEffect() 代码块：

const [missingTradingSystemNameError, setMissingTradingSystemNameError] = React.useState(false);
const [duplicateTradingSystemNameError, setDuplicateTradingSystemNameError] = React.useState(false);

...

React.useEffect(() => {
    if (props.tradingSystemDialog && resetTradingSystemDialogOnNextOpen) {
      ...
      
      setMissingTradingSystemNameError(false);
      setDuplicateTradingSystemNameError(false);
      
      ...
    }
  }, [
    props.tradingSystemDialog,
    resetTradingSystemDialogOnNextOpen,
    tickFields,
    consolidatedFields
  ]);

missingTradingSystemNameError是通过setMissingTradingSystemNameError设置的，而duplicateTradingSystemNameError是通过setDuplicateTradingSystemNameError设置的。如您所见，这些有状态变量可能在 useState() 中被更改，但它们不在 useState() 的依赖项中。

标签： javascriptnode.jsreactjsjsxconditional-operator

解决方案

Providing a minimal reproducible example would be the best, but the context is too complex in my case. However, what I did is to remove more and more code to examine if one small part is causing the issue. Now I came to the conclusion that the following code snippet at some other location in the file is problematic and causes the mentioned code to fail or at least behave in a strange way:

...
{
  basicShortSettingsError
  ?
    <div className={classes.error}>
      <ErrorOutline
        className={classes.errorIcon}
      />
      <Typography className={classes.sectionError} variant="body2">
        {
          parseFloat(positionSizeShort) > parseFloat(maxContractsShort)
          ?
            "Position size > maximum contracts"
          :
            "Set position size and maximum contracts"
        }
      </Typography>
    </div>
  :
    null
}
...

For some reason, the conditional part inside the Typography tag worked before but is now causing errors if I extend the code at some other point in the file by the content which I mentioned in the question.

To clarify, this is the code snippet causing problems:

<Typography className={classes.sectionError} variant="body2">
  {
    parseFloat(positionSizeShort) > parseFloat(maxContractsShort)
    ?
      "Position size > maximum contracts"
    :
      "Set position size and maximum contracts"
  }
</Typography>

positionSizeShort and maxContractsShort are also stateful variables and I am not sure why the code was working just fine before and is now failing, but at least I have found the problem's root now where I can probably do a workaround.

If anyone has a better idea why exactly this code is problematic, it is more than welcomed to share your thoughts here as I have no real answer for my issue.

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