为什么我的 Redux 减速器认为我的状态是未定义的?

问题描述

我相信我正在逐行复制 Todo 教程，但出现此错误:

I believe I'm copying the Todo tutorial pretty much line for line, I am getting this error:

错误:ReduceraddReport"在初始化期间返回未定义.如果传递给 reducer 的状态未定义，则必须显式返回初始状态.初始状态可能不是未定义的.

这是我的 addReport 减速器:

And here is my addReport reducer:

const addReport = (state = [], action) =>
{
  console.log(state)
  switch (action.type) {
    case ADD_NEW_REPORT:
    return [...state,
      addReports(undefined, action)
    ]
    }
}

我添加了日志语句并且可以验证它是否返回一个空数组.即使将 state 设置为 1 之类的值也会产生相同的结果.我错过了什么?

I added the logging statement and can verify that it returns an empty array. Even setting state to something like 1 will produce the same results. What am I missing?

推荐答案

您缺少 switch case 的 default.

You are missing the default of the switch case.

default: {
  return {
    ...state
  }
}

如果您忘记了 Redux，它就不会像一个好孩子一样玩！

Redux won't play along like a nice kid if you forget to do it!

或者，您可以在最后明确返回初始状态:如果传递给reducer的状态未定义，则必须显式返回初始状态.

Or alternatively, you can explicitly return at the end the initial state:If the state passed to the reducer is undefined, you must explicitly return the initial state.

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