Question

我正在使用承诺。这是我的问题here

的延续

我遇到的问题是响应，即一个对象数组具有空值。我会尝试解释这个

首先我得到userId
从userId获取用户whishlist产品
然后使用userId我得到商店/商店列表
然后我遍历商店列表并调用另一个API来检查这个商店是否是用户最喜欢的商店。

然后我获取每个商店的产品并附加到一个对象中并返回。

 int ReadScores(string fileName, string names[], float avg_scores[], int array_size){

int linesCounted = 0;
float indScores[array_size];

int lineCounter = 0;
string myLine, nameSubString, scoreSubString;
float scoreConvert = 0.0;
float averageScores = 0.0;

ifstream myFileIn;
//open the file
myFileIn.open(fileName, ios::in);
    if (myFileIn.fail()){
        cout << "Error opening "<< fileName << endl;
        return 0;
    }
    int index = 0;
    //read the file until the end of file is reached
    while (getline(myFileIn, myLine)){
            //firstComma will hold the integer value of the index position of the first comma found
            int firstComma = myLine.find(',');
             //this should grab the the names at the beginning of each string on each new line
            nameSubString = myLine.substr(0, firstComma);
            names[index] = nameSubString;


            int startingPos = 0;
            float commaCounter = 0;
            //find how many commas are in a string and use that to limit your loop
            for (int ind = 0; ind < myLine.length(); ind++){
                if (myLine[ind] == ',')
                    commaCounter++;
                }

            for (int ind = 0; ind < commaCounter; ind++){
                     //grab the first number and store it the scoreSubString variable
                    int found = myLine.find(',', firstComma) + 1;
                    scoreSubString = myLine.substr(found, myLine.find(',', found));
                    //change the value of firstComma to the next index location
                    firstComma = found + 1;

                    ///convert string to number
                    stringstream(scoreSubString) >> scoreConvert;
                    ///store number in float array
                    indScores[ind] = scoreConvert;
                }

        averageScores = 0;
            for (int ind = 0; ind < commaCounter; ind++){
                averageScores = indScores[ind] + averageScores;
                }
                float averageOverall = averageScores/commaCounter;
                avg_scores[index] = averageOverall;
        index++;
        if (!myLine.empty()){
                lineCounter++;
            }
        }
    myFileIn.close();

我得到的回应是

function getStoresList(context) {
    const userID = common.getUserID(context)
    let userWishListProd = []

    return userID
        .then(uid => Wishlist.getUserWishlistProducts(uid).then((products) => {
            userWishListProd = products.data.map(product => +product.id)
            return uid
        }))
        .then(uid => api.getOfficialStoresList(uid).then((response) => {
                if (!response.data) {
                    const raw = JSON.stringify(response)
                    return []
                }

                const shops = response.data
                return Promise.all(
                        shops.map((shop) => {
                            const id = shop.shop_id
                            const shopobj = {
                                id,
                                name: shop.shop_name,
                            }
                            return favAPI.checkFavourite(uid, id)
                                .then((favData) => {
                                    shopobj.is_fave_shop = favData

                                    // Fetch the products of shop
                                    return getProductList(id, uid)
                                        .then((responsedata) => {
                                            shopobj.products = responsedata.data.products.map(product => ({
                                                id: product.id,
                                                name: product.name,
                                                is_wishlist: userWishListProd.indexOf(product.id) > -1,
                                            }))
                                            return shopobj
                                        })
                                        .catch(() => {})
                                })
                                .catch(err => console.error(err))
                        }))
                    .then(responses => responses)
                    .catch(err => console.log(err))
            })
            .catch(() => {}))
        .catch()
}

实际商店的数量是4，但是不会追加null。我在这里做Promise有什么问题。

Answer 1

您是否调试了代码？我会在Chrome上调试并在代码上添加一些断点，以查看实际响应是什么。

Answer 2

这似乎与您的.catch(() => {})和.catch(err => console.error(err))调用有关。如果循环中的一个promise有错误，它将转换为undefined值（可选择在之前报告），以便Promise.all符合可能包含undefined值的数组。如果您JSON.stringify，那么您将获得null这些索引。

删除无效的.catch(() => {})语句（或将其替换为日志记录），并检查错误日志。

从Promise.all获取值为null

2 个答案: