为什么.then不是函数? [英] Why .then is not a function?

问题描述

service.js

.factory('EventService', function ($http, $cordovaSQLite) {
    return {
        //some code here..
        populateData: function (data) {
            var items = [];
            for (i = 0; i < data.length; i++) {
                items.push(data[i]);
            }
            return items;
        }
    }
})

controller.js

.controller('NearCtrl', function ($scope, $http, $cordovaSQLite, EventService) {
    EventService.getDataFromDB().then(function (result) {
        if (result.length > 0) {
            EventService.populateData(result).then(function (items) {
                $scope.items = items;
            })
        } else {
            EventService.getDataFromApi().then(function () {
                EventService.getDataFromDB().then(function (result) {
                    EventService.populateData(result).then(function (items) {
                        $scope.items = items;
                    })
                })
            })
        }
    });
})

当我尝试运行此代码时，出现"TypeError:EventService.populateData(...).然后不是函数".

我在做什么错?谢谢.

解决方案

该服务需要返回承诺，而不返回项目

populateData: function(data) {
    var deferred = $q.defer();
    var items = [];
    for (i = 0; i < data.length; i++) {
        items.push(data[i]);
    }
    deferred.resolve(items);
    return deferred.promise;
}

尽管您可能会这样做，但您可能并不需要

var items = EventService.populateData(result);
//Do something with items here

通常在您异步执行某些操作时使用promises.就像调用API并等待响应一样.在这些情况下，响应可能需要几秒钟才能完成，然后调用.then函数.在您的情况下，如果您将该函数作为一个承诺，它将几乎立即被调用

这是$ q文档 AngularJS:API:$ q

service.js

.factory('EventService', function ($http, $cordovaSQLite) {
    return {
        //some code here..
        populateData: function (data) {
            var items = [];
            for (i = 0; i < data.length; i++) {
                items.push(data[i]);
            }
            return items;
        }
    }
})

controller.js

.controller('NearCtrl', function ($scope, $http, $cordovaSQLite, EventService) {
    EventService.getDataFromDB().then(function (result) {
        if (result.length > 0) {
            EventService.populateData(result).then(function (items) {
                $scope.items = items;
            })
        } else {
            EventService.getDataFromApi().then(function () {
                EventService.getDataFromDB().then(function (result) {
                    EventService.populateData(result).then(function (items) {
                        $scope.items = items;
                    })
                })
            })
        }
    });
})

When I'm trying to run this code, I get "TypeError: EventService.populateData(...).then is not a function".

What am I doing wrong ? Thanks.

解决方案

that service needs to return a promise, not returning the items

populateData: function(data) {
    var deferred = $q.defer();
    var items = [];
    for (i = 0; i < data.length; i++) {
        items.push(data[i]);
    }
    deferred.resolve(items);
    return deferred.promise;
}

you might not need this though since you could do

var items = EventService.populateData(result);
//Do something with items here

usually promises are used if you're doing something asynchronously. Like calling an API and waiting for a response. In those cases, the response might take seconds to finish THEN the .then function gets called. in your case if you make that function a promise it will be called almost immediately

EDIT: Here's the link to $q Documentation AngularJS: API: $q

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