javascript - Angular Service "Unable to get property ' then' 未定义或空引用”

Question

您好，我不知道如何返回服务的正确功能/部分，因为它是由于 Yammer API 而进行分页的。

我已阅读文档并尝试返回整个函数，但我花了很长时间在它上面，我开始绝望，请帮助我。

我认为返回在错误的地方 - 我收到错误:

"Unable to get property 'then' of undefined or null reference"

我的 Controller

app.controller("mainController", function($scope, $http, yammerREST) {

    $scope.getYammerPosts = function () {
                yammerREST.getYammerData($scope.yammerURL).then(function(data) {
                        $scope.results = data.results;
                });
    };
});

我的服务

app.service("yammerREST", function($http) {
    this.getYammerData = function(url) {

        var groupID = url.split("feedId=")[1];
        console.log(groupID);
        var baseURL = "https://www.yammer.com/api/v1/messages/in_group/" + groupID + ".json?threaded=true";
        var url = baseURL;
        var results = [];

        getPosts();

        function getPosts () {
        return $http({
                url: url,
                method: "GET",
                headers: { "Accept": "application/json; odata=verbose" }
             }).then(function(response) {
                    results = results.concat(response.data.messages);
                    console.log(results);

                    if (response.data.meta.older_available == true) {
                            url = baseURL + "&older_than=" + results[results.length-1].id;
                            getPosts();
                    };

                    return {
                        yammerListName: response.data.meta.feed_name,
                        results: results,
                    };
            }).catch(function(e){
                console.log("Error: ", e);
            });
        };
    };
});

Answer 1

“Unable to get property 'then' of undefined or null reference”

该错误消息通常意味着该函数未能 return promise :

app.service("yammerREST", function($http) {
    this.getYammerData = function(url) {

        var groupID = url.split("feedId=")[1];
        console.log(groupID);
        var baseURL = "https://www.yammer.com/api/v1/messages/in_group/" + groupID + ".json?threaded=true";
        var startURL = baseURL;
        var results = [];

        //vvvv RETURN promise
        return getPosts(baseURL,startURL);

        function getPosts (baseURL, url) {
            //vvvv RETURN promise
            return $http({
                url: url,
                method: "GET",
                headers: { "Accept": "application/json; odata=verbose" }
            }).then(function(response) {
                    results = results.concat(response.data.messages);
                    console.log(results);

                    if (response.data.meta.older_available == true) {
                        var nextURL = baseURL + "&older_than=" + results[results.length-1].id;
                        //vvvv RETURN promise
                        return getPosts(baseURL,nextURL);
                    };

                    return {
                        yammerListName: response.data.meta.feed_name,
                        results: results,
                    };
            }).catch(function(e){
                console.log("Error: ", e);
                //IMPORTANT to re-throw error
                throw e;
            });
        };
    };
});

正在递归调用 getPosts 函数。为了进行有效的递归，f(x) 必须调用 f(x+1) 直到满足某个结束条件。

此外，在 .catch block 中，re-throw errors 也很重要。为了跳过 promise 链中的后续 .then block 。