使用APP_INITIALIZER的角加载配置

Question

我正在尝试使用Angular 8中的APP_INITIALIZER通过服务加载配置文件（json）。配置包含缩略图的图像和道具的路径

app-config.json

    {
  "substitutePictureLink": "../images/not_found.png",
  "noImageFound": "../images/404_not_found.png",
  "thumbnailProps": {
  "width": "400",
    "height": "400",
    "format": "PNG",
    "view": "Interior",
    "withdimensions": "true",
    "withdescription": "true"
  }
}

为了加载配置，我创建了一个服务[app-config-service]，它看起来像这样：

app-config-service.ts

export class AppConfigService {

public get appConfig(): any {
    return this._appConfig;
}

public set appConfig(value: any) {
    this._appConfig = value;
}

private _appConfig: any;

constructor(
        private _httpClient: HttpClient,
    ) {
        console.log('constructor app-config-service'); 
        this.loadAppConfig();
    }

public loadAppConfig(): any { 
//also tried a promise here
    return this._httpClient.get('../../../assets/configs/app-config.json')
        .pipe(
            take(1)
        )
        .subscribe(
            (config) => {
                this._appConfig = config;
            }
        );

}

所以我需要在启动时加载配置；

app-module.ts

providers: [
    AppConfigService,
    {
        provide: APP_INITIALIZER,
        multi: true,
        deps: [AppConfigService],
        useFactory: (appConfigService: AppConfigService) => {
            return () => {
                return appConfigService.loadAppConfig();
            };
        }
    }
],
bootstrap: [AppComponent],
})

export class AppModule {
}

当我尝试加载配置时，它看起来像这样：

some-service.ts

    export class someService {

private _noImageFound = this._appConfigService.appConfig.noImageFound;

constructor(
        private _appConfigService: AppConfigService
    ) {
    }

...

public getThumbnail(): Observable<SafeUrl> {
        return this._httpClient.get(this._apiUrl + '/visual-tree/thumbnail?width=400&height=400', {
            responseType: 'blob',
        })
            .pipe(
                map((res: Blob): SafeUrl => this._blobToUrl.transform(res)),
                catchError((err: HttpErrorResponse): Observable<string> => {
                    this._logger.error(ErrorMessage.thumbnailNotLoaded, err);
                    return of(this._noImageFound);
                })
            );
    }
...

错误：

• 未捕获的TypeError：无法读取未定义的属性'noImageFound'

此错误在登录后立即发生。有趣的是，app-config-service的构造函数被调用了两次。我的猜测是，该服务的引用发生了一些奇怪的事情。

Answer 1