打字稿 await toPromise 类型转换错误

Question

我有以下问题：

export class FloorManagerComponent implements OnInit
{
    public meta = {
        list: [],
        building: Building,
        loading: true,
    };

    constructor(
        private router: Router, 
        private activatedRoute: ActivatedRoute, 
        private buildingService: BuildingService
    )
    {;}

    public async ngOnInit() 
    {
        let params = await this.activatedRoute.params.first().toPromise();

        this.meta.building = await this.buildingService // line 42: ERROR
            .getBuilding(params['buildingId'])          // line 42: ERROR
            .toPromise();                               // line 42: ERROR
    }

    ...
}

我在编译过程中遇到以下错误：

[at-loader] ./src/pages/floor/manager/floorManager.component.ts:42:9 TS2322：类型“Building”不可分配给类型“typeof Building”。 “建筑”类型中缺少属性“原型”。

我被困在这里 - 知道吗？

以下是使用的类的主体：

export class Building {

    constructor(
        public id: number,
        public name: string, 
        public image_url: string, 
    ) {}

    ...
}


export class BuildingService {

    public getBuilding(buildingId: number)
    {
        return this.http.get(Url.api('buildings/' + buildingId))
            .map( (response) => { 
                return Obj.cast(response, Building);                  
            } );
    }

    ...

}

export class Obj {

    /**
     * This method allow to cast json (and not only) obiects to given type including methods
     * CAUTION: Constructor of 'type' T of object obj is never call during casting
     * Example usage:
     *
     * let space: Space = this.cast(spaceFromJson,Space);
     *
     * (we use type: { new(...args): T} tp creeate fat arrow functions in prototpye...  https://stackoverflow.com/a/32186367/860099)
     *
     * @param obj object (from json) that has only fields and no methods
     * @param type desired type
     * @returns {any} object that hava fields from obj and methods from type
     */
    public static cast<T>(obj, type: { new(...args): T} ): T 
    {
        obj.__proto__ = type.prototype;
        return obj;
    }
    ...
}

Answer 1

我找到了解决方案：

public meta = {
    list: [],
    building: null as Building,
    loading: true,
};

所以我们应该将building: Building改为building: null as Building 。 因为我们在meta字段定义中使用“对象符号”，错误是我在子字段building使用了“非对象符号”（在“对象符号”中:将含义从类型更改为值定义）。