React Native、redux、redux-saga发起请求全过程简单解说

以下代码来源于我的项目NovelAPP：https://github.com/SemperChen/NovelAPP

 

首先是从this.props.dispatch发起网络请求，如MainDetail（BookDetailPage的子组件）

js/commons/MainDetail.js

下面是请求书籍详情， bookDetailUrl是请求书籍详情网址

 componentDidMount() {
    ...
    this.props.dispatch(requestDetail(this.bookDetailUrl))
    ...
 }

js/actions/detail.js

...
export function requestDetail(bookDetailUrl) {
    return {
        type: REQUEST_DETAIL,
        bookDetailUrl
    };
}
...

我们从上面代码可以看出，其实

requestDetail(this.bookDetailUrl)

这个方法返回的就是以下这个action对象

{
        type: REQUEST_DETAIL,
        bookDetailUrl
}

即代码

this.props.dispatch(requestDetail(this.bookDetailUrl))

可以看成

    this.props.dispatch({
        type: REQUEST_DETAIL,
        bookDetailUrl
    })

当dispatch把action即{ type: REQUEST_DETAIL, bookDetailUrl } 发出去之后，redux收到这个action请求，会执行以下代码中的detail(state=initalState, action)方法

js/reducers/detail.js

export default function detail(state = initialState, action) {
    switch (action.type) {
        case REQUEST_DETAIL:
        return {
            ...state,
            isFetchingDetail:true
        };
        ...
    }
}

并返回以下对象

{
    ...state,
    isFetchingDetail:true
};

然后会执行以下代码中mapStateToProps这个方法 ，将isFetchingDetail=true传进来

js/commons/MainDetail.js

function mapStateToProps(state) {
    const {bookDetail, isFetchingDetail} = state.detail;
    const {items: bookmarks} = state.bookmarks;
    return {bookDetail, bookmarks, isFetchingDetail}
}

上面mapStateToProps方法执行后，会重新渲染render等方法

 render() {
        ...
        return (
            
                        
            {this.props.isFetchingDetail
                 ?
                 
                    
                           加载中，        
                           请稍等
                 

                 : null
             }
            ...
            
        )
    }

这时，因为上面代码中this.props.isFetchingDetail=true，加载中，请稍等 这几个字便出现，如图

与此同时saga也收到REQUEST_DETAIL请求

js/sagas/index.js

const rootSaga = function* root() {
    yield all([
        ...
        takeLatestFetch(REQUEST_DETAIL,fetchBookDetail),
        ...
    ])
};
export default rootSaga;

以上takeLatestFetch(REQUEST_DETAIL, fetchBookDetail)，这个方法监听到REQUEST_DETAIL请求后，就会执行fetchBookDetail 这个方法，并将action即{ type:  REQUEST_DETAIL, bookDetailUrl }中bookDetailUrl作为参数

js/sagas/detail.js

export function* fetchBookDetail(params) {
    try {
        const {bookDetailUrl} = params;
        const bookDetail = yield call(fetchJSON, bookDetailUrl);
        yield put(receiveDetail(bookDetail))
    } catch (e) {
        console.log('detail fetchBookDetail:', e.message);

    }

};

 

const bookDetail = yield call(fetchJSON, bookDetailUrl);

 执行到上面这一步的时候，会把bookDetailUrl网址作为fetchJSON方法的参数，发起网络请求，并将请求结果返回，即bookDetail

js/utils/HttpUtil

export function fetchJSON(url) {
    return new Promise((resolve, reject) => {
        fetch(url, {
            headers: {
                'Content-Type': 'application/json',
                'Accept-Charset': 'utf-8',
                'User-Agent': 'Mozilla/5.0 (Linux; X11)',
            }
        })
            .then((response) => {
                return response.json()
            })
            .catch((error) => {
                reject(error);
            }).then((responseData) => {
            if (!responseData) {
                reject(new Error('fetchJSON:responseData is null'));
                return;
            }
            resolve(responseData);
        }).done();
    })
}

 

yield put(receiveDetail(bookDetail))

执行到这一步时候，saga会将网络请求返回的结果bookDetail发出去，类似于刚开始介绍的this.props.dispatch

 

js/actions/receiveDetail.js

export function receiveDetail(bookDetail) {
    return {
        type: RECEIVE_DETAIL,
        bookDetail
    };
}

因为receiveDetail(bookDetail) 返回的值是{ type:  RECEIVE_DETAIL, bookDetail } ，所以yield put(receiveDetail(bookDetail))相当于

yield put({
        type: RECEIVE_DETAIL,
        bookDetail
    })

或相当于

this.props.dispatch({
        type: RECEIVE_DETAIL,
        bookDetail
    })

然后redux收到RECEIVE_DETAIL请求后，会执行以下方法，并将action：{type:  RECEIVE_DETAIL, bookDetail}传到下面代码里，然后action.type跟case RECEIVE_DETAIL匹配，返回{ ...state, bookDetail:  action.bookDetail, isFetchingDetail: false }

js/reducers/detail.js

export default function detail(state = initialState, action) {
    switch (action.type) {
       ...
        case RECEIVE_DETAIL:
            return {
                ...state,
                bookDetail: action.bookDetail,
                isFetchingDetail:false
            };
        ...
    }
}

然后会将上面bookDetail和isFetchingDetail传到mapStateToProps

js/commons/MainDetail.js

function mapStateToProps(state) {
    const {bookDetail, isFetchingDetail} = state.detail;
    const {items: bookmarks} = state.bookmarks;
    return {bookDetail, bookmarks, isFetchingDetail}
}

render将重新渲染，返回的bookDetail书籍详情将会显示

render(){
   ...
   this.bookDetail = this.props.bookDetail;
   return(
    
      ...
      {this.bookDetail.bookName}
      ...
    
   )
   ...

}

因为返回的 isFetchingDetail=false，下图中的加载中，请稍等将消失