Question

我被迫在此处使用Promises with Observables，因为在Angular应用程序中加载数据时，它要求您将APP_INITIALIZER与返回的promise一起使用。这就是为什么我在诺言中创建一个可观察的东西。调试它以查看为什么我的数据未加载到表中后，我发现实例数据成员this.tableDataObs在以后使用getTableModelDataSource（tableName：string）方法被调用时没有任何预订，我无法明白为什么？它在承诺中确实具有价值。发生了什么事？

export class UiDataService {
    tableDataObs: Observable<TableModel[]>;

    constructor(private httpClient: HttpClient) {
        this.tableDataObs = new Observable<TableModel[]>();
    }

    loadTableData(): Promise<any> {
        return new Promise((resolve, reject) => {
            this.httpClient
                .get('/assets/data/tables.json')
                .map((tables: JSON) => {
                const tableModels: TableModel[] = this.createTableModels(tables);
                this.tableDataObs = of(tableModels); // tableModels has array value here
                // this.tableDataObs.subscribe(s => console.log(s)); again subscribing to observable here returns array 
            })
            .subscribe(() => {
                resolve(true);
            });
        });
    }

    getTableModelDataSource(tableName: string): TableModelDataSource {
        this.tableDataObs.subscribe(s => console.log(s)); // this.tableDataObs has nothing to subscribe to here? WHY?
    ...
    }

加载数据调用是从导入到AppModule的SharedModule中进行的

imports ...

export function tableFactory(provider: UiDataService) {
    return () => provider.loadTableData();
}


@NgModule({
    imports: [
        ...
    ],
    declarations: [
        ...
    ],
    entryComponents: [...],
    providers: [
        ...
        UiDataService,
        { provide: APP_INITIALIZER, useFactory: tableFactory, deps: [UiDataService], multi: true },
    ],
    exports: [
      ...
    ]
})
export class SharedModule {}

和getTableModelDataSource方法调用发生在具有需要数据源的mat表的组件中

使用'of'运算符创建Observable后，订阅不可用（需要Root和Singleton服务）

0 个答案: