如何在反应中获取部分数据，redux？

Question

动作

import { FETCH_BLOG, FETCH_BLOG_ERROR, FETCH_BLOG_LOADING } from "../constants/blogActionTypes"
    
    const initialState = {
        blogs: [],
    error: '',
    loading: false,
    allBlogs: []
}
// eslint-disable-next-line import/no-anonymous-default-export
export default (blogs = initialState, action) => {
    switch (action.type) {
        case FETCH_BLOG_LOADING:
            return {
                blogs: [...blogs.blogs],
                loading: true,
                error: ''
            };
        case FETCH_BLOG_ERROR:
            return {
                blogs: [...blogs.blogs],
                loading: false,
                error: action.payload
            };
        case FETCH_BLOG:
            return {
                blogs: [...action.payload, ...blogs.blogs],
                loading: false,
                error: ''
            };
        default: return blogs;
    }
}

减速器

export const fetchBlogs = (data) => async (dispatch) =>{

    dispatch({ type: FETCH_BLOG_LOADING, payload: true })
    fetch('http://localhost:5000/blog?show=' + data, {
        method: 'GET',
        headers: {
            authorization: userData.token
        }
    })
        .then(res => res.json())
        .then(data => {
            if (data.message) {
                dispatch(fetchBlogsError(data.message))
            } else {
                dispatch({ type: FETCH_BLOG, payload: data })
            }
        })
}

反应

const [fetchData, setFetchData] = useState(0);
    const showData = () => {
        setFetchData(fetchData + 10)
    }

    const dispatch = useDispatch();

    const { loading, error, blogs, } = useSelector(state => state.blogs)
  
    const getData = useCallback(  () => {
        dispatch(fetchBlogs(fetchData))
    }, [fetchData])

    useEffect(() => {
        getData()
    }, [getData])

在第一次渲染时，我获取了 10 个项目。单击加载更多后，我从数据库中获取了另外 10 个数据。在博客组件上它很好，但是返回主页并返回博客页面后；博客项目重复。如何解决此重复问题>

Answer 1

这里有两个相互关联的问题，你可能不需要解决#2，这取决于你如何解决#1。

1. 您应该向您的 thunk 操作添加一个条件，这样您就不会抓取您之前抓取过的页面。
2. 您应该按页面分隔您的博客项目，这样如果您两次获取第 1 页，您就不会总是将最新的项目附加到数组的末尾。

旁注：[...blogs.blogs] 是不必要的，因为有理由克隆您没有更改的属性。

我对您的 API 调用感到困惑。看起来/blog?show=20 正在获取帖子 21-30，但我认为基于名称 show 它将是帖子 1-20。

使用位置索引：

import { createAsyncThunk, createReducer } from "@reduxjs/toolkit";

export const fetchBlogs = createAsyncThunk(
  "blogs/fetchBlog",
  async (startIndex, { getState, rejectWithValue }) => {
    const res = await fetch("http://localhost:5000/blog?show=" + startIndex, {
      method: "GET",
      headers: {
        // where does userData come from ??
        authorization: userData.token
      }
    });
    const data = await res.json();
    if (data.message) {
      rejectWithValue(data.message);
    } else {
      return data;
    }
  },
  {
    condition: (startIndex, { getState }) => {
      const { blogs } = getState();
      // cancel if loading of if first post on paage is loaded
      if (blogs.loading || blogs.blogs[startIndex]) {
        return false;
      }
    }
  }
);

const initialState = {
  blogs: [],
  error: "",
  loading: false
};

export default createReducer(initialState, (builder) =>
  builder
    .addCase(fetchBlogs.pending, (state) => {
      state.loading = true;
      state.error = "";
    })
    .addCase(fetchBlogs.rejected, (state, action) => {
      state.loading = false;
      state.error = action.payload ?? action.error;
    })
    .addCase(fetchBlogs.fulfilled, (state, action) => {
      const startIndex = action.meta.arg;
      const newBlogs = action.payload;
      // insert in the array at the correct position
      state.blogs.splice(startIndex, newBlogs.length, newBlogs);
    })
);

使用分隔页：

import { createAsyncThunk, createReducer, createSelector } from "@reduxjs/toolkit";

export const fetchBlogs = createAsyncThunk(
  "blogs/fetchBlog",
  async (pageNumber, { getState, rejectWithValue }) => {
      const startIndex = 10 * (pageNumber - 1);
    const res = await fetch("http://localhost:5000/blog?show=" + startIndex, {
      method: "GET",
      headers: {
        // where does userData come from ??
        authorization: userData.token
      }
    });
    const data = await res.json();
    if (data.message) {
      rejectWithValue(data.message);
    } else {
      return data;
    }
  },
  {
    condition: (pageNumber, { getState }) => {
      const { blogs } = getState();
      // cancel if loading of if there is a property for this page
      if (blogs.loading || blogs.blogs[pageNumber]) {
        return false;
      }
    }
  }
);

const initialState = {
  //arrays keyed by page number
  blogs: {},
  error: "",
  loading: false
};

export default createReducer(initialState, (builder) =>
  builder
    .addCase(fetchBlogs.pending, (state) => {
      state.loading = true;
      state.error = "";
    })
    .addCase(fetchBlogs.rejected, (state, action) => {
      state.loading = false;
      state.error = action.payload ?? action.error;
    })
    .addCase(fetchBlogs.fulfilled, (state, action) => {
      const pageNumber = action.meta.arg;
      state.blogs[pageNumber] = action.payload;
    })
);

// want to flatten the blogs array when selecting
// create a memoized selector
export const selectBlogs = createSelector(
    state => state.blogs,
    (blogsState) => ({
        ...blogsState,
        blogs: Object.values(blogsState.blogs).flat(1)
    })
)

带组件：

export default () => {
  const [pageNumber, setPageNumber] = useState(1);

  const showNext = () => {
    setPageNumber((page) => page + 1);
  };

  const dispatch = useDispatch();

  const { loading, error, blogs } = useSelector(selectBlogs);

  useEffect(() => {
    dispatch(fetchBlogs(pageNumber));
  }, [dispatch, pageNumber]);