javascript - 如何在不使用 $scope $watch 的情况下等到变量被定义？

Question

下面是我目前的代码:
我的模块

module App.SomeModule {

    import ILabelSettingsViewModel = App.GeneralSettings.data.ILabelSettingsViewModel;
    import IGeneralSettingsService = App.GeneralSettingsService.IGeneralSettingsService;

    export enum LabelPageFormat {
        A4,
        Thermal
    }

    export interface IConsignmentDataService {
        getAccountLabelFormat(): LabelPageFormat;
    }

    export class MyDataService implements IMyDataService {
        accountLabelFormat: LabelPageFormat;
        static $inject: string[] = ["generalSettingsService"];
        constructor(private generalSettingsService: IGeneralSettingsService) {
            this.determineAccountLabelFormat();
        }
        getAccountLabelFormat(): LabelPageFormat {
            return this.accountLabelFormat;
        }
        private determineAccountLabelFormat() {
            var that = this;
            this.generalSettingsService.getLabelSettings().then((data: ILabelSettingsViewModel) => {
                switch (data.name) {
                    case LabelPageFormat[LabelPageFormat.Thermal]:
                        that.accountLabelFormat = LabelPageFormat.Thermal;
                        break;
                    default:
                        that.accountLabelFormat = LabelPageFormat.A4;
                        break;
                }
            }, () => {
                that.accountLabelFormat = LabelPageFormat.A4;
            });
        }
    }
    angular.module("app.common").service("myDataService", MyDataService);
}     

和我的 Controller

module App.Consignment.List {
    "use strict";
    import IConsignmentDataService = Consignment.IConsignmentDataService;
    import ConsignmentListGridScope = Consignment.IConsignmentListGridScope;

    class ConsignmentListController implements IConsignmentBulkActionProvider {
        accountLabelFormat: LabelPageFormat;
        static $inject = ["$scope", "myDataService"];
        constructor(private $scope: ConsignmentListGridScope, private myDataService: IMyDataService) {
            this.accountLabelFormat = this.consignmentDataService.getAccountLabelFormat();
        }
    }
    angular.module("app.consignment").controller("consignmentListController", ConsignmentListController);
}

我想做的是，从我的数据服务中获取 accountLabelFormat，然后将其用于其他地方。在数据服务中，一种方法用于从数据库中获取格式，该格式作为 promise 返回，然后如果成功，我将设置在调用 getAccountLabelFormat() 方法时返回的变量我的 Controller 。现在我的问题是，由于服务方法是异步的，当我调用 getAccountLabelFormat() 方法时，accountLabelFormat 服务中的变量尚未设置，因此每个时间我在我的 Controller 中得到一个未定义的值。关于如何解决这个问题的任何想法？提前致谢。

Answer 1

使用$q.when。查看https://docs.angularjs.org/api/ng/service/ $q

例如:

$q.when(this.accountLabelFormat)

所以当你请求那个值时，它会返回一个 promise，然后将它链接到一个 then 语句