反应钩子，状态没有正确改变

Question

在这个项目中，我使用了 React 钩子，这个片段用于改变项目的颜色主题，但有一个我无法解决的问题。 const lightTheme = { ... }

  const darkTheme = {
     ...
  }
 export const ThemeState = ({children}) => {

  const initialState = {
     theme: lightTheme
  }

  const [state, dispatch] = useReducer(ActionReducer, initialState)

  const {theme} = state 

  const themeToggler = (e) => {
     e.preventDefault()
     console.log(theme)
     if(theme == lightTheme){
        dispatch({type:THEME, payload: darkTheme})
     }
     else if(theme == darkTheme){
        dispatch({type:THEME, payload: lightTheme})
     }
   }

Lorem ipsum dolor sat amet，consectetur adipiscing elit，sed do eiusmod tempor incididunt ut Labore et dolore magna aliqua。

我的减速机：

export const ActionReducer = (state, action) => {
         switch(action.type) {
           case THEME:
             return{
               ...state,
               theme: action.payload
            }
           default:
              return state
   }
};

Here is component with toggle button by each click, I need to change theme in state, it clicks correctly: 

import {ThemeContext} from '../../store/themeState'

function Main () {
  const {theme, themeToggler} = useContext(ThemeContext)
   return (
       <button onClick={e => {themeToggler(e)}}></button>
   )
}

 export default Main

 when I press the button i catch this log


    ({body: "#E2E2E2", text: "#363537"}
      {body: "#363537", text: "#FAFAFA"}
      {body: "#363537", text: "#FAFAFA"}
      ....)

I don't know why do state changes like this. If you can, help me to solve this bug.)

Answer 1

初始主题是body: '{#E2E2E2', text: '#363537'} 。

当您单击按钮时，您会记录此主题{body: "#E2E2E2", text: "#363537"} ，这正是您的初始主题。

登录后，将主题更新为深色主题{body: '#363537', text: '#FAFAFA'} 。

这将被记录，一旦您再次单击按钮： {body: "#363537", text: "#FAFAFA"} 。

现在问题来了，由于您在每次渲染时都创建了 darkTheme 对象，因此引用与之前的不一样，因此else if(theme == darkTheme)失败，因为 darkTheme 对象与之前的 darkTheme 对象不同。

要么将主题对象生成移出组件，这样您就不会在每次渲染时生成一个新对象或向主题添加类型：

const lightTheme = {
  body: '#E2E2E2',
  text: '#363537',
  type: "light"
}`

并比较那些： if(theme.type == darkTheme.type)

Answer 2

您需要的是在按钮单击时切换主题：

所以你可以这样做：

主题状态

import React, { useReducer } from "react";
import { TOGGLE_THEME } from "./ActionTypes";
import ActionReducer from "./ActionReducer";

const lightTheme = {
  body: "#E2E2E2",
  text: "#363537"
};

const darkTheme = {
  body: "#363537",
  text: "#FAFAFA"
};

const initialState = {
  isLightTheme: true
};

export const ThemeState = ({ children }) => {
  const [state, dispatch] = useReducer(ActionReducer, initialState);

  const { isLightTheme } = state;

  const themeToggler = e => {
    e.preventDefault();
    dispatch({ type: TOGGLE_THEME });
  };

  const backgroundColor = isLightTheme ? lightTheme.body : darkTheme.body;
  const fontColor = isLightTheme ? lightTheme.text : darkTheme.text;

  return (
    <div style={{ backgroundColor: `${backgroundColor}` }}>
      <p style={{ color: `${fontColor}` }}>Some Text</p>
      <button type="submit" onClick={themeToggler}>
        Toggle Theme
      </button>
      <hr />
      Current Theme: {isLightTheme ? "light" : "dark"}
    </div>
  );
};

动作减速器：

import { TOGGLE_THEME } from "./ActionTypes";

export default function(state, action) {
  switch (action.type) {
    case TOGGLE_THEME:
      return {
        ...state,
        isLightTheme: !state.isLightTheme
      };
    default:
      return state;
  }
}

动作类型：

export const TOGGLE_THEME = "TOGGLE_THEME";

代码沙盒

Answer 3

我创建了这种行为如何小例子可以实现：

const darkTheme = {
  color: "green"
};

const lightTheme = {
  color: "red"
};

export default function App() {
  const [useLightTheme, setUseLightTheme] = useState(true);

  return (
    <div className={useLightTheme ? darkTheme.color : lightTheme.color}>
      <button onClick={() => setUseLightTheme(!useLightTheme)}>toggle</button>
      some example text
    </div>
  );
}

由于您没有提供所有相关代码（例如减速器），我无法解释您的代码。