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类型Observable<Observable<any[]>>不可分配给类型Observable<any[]>

rxjs5 rxjs typescript angular

6324 · 技术社区 · 8 年前

我正在使用数据库服务中的数据实现自动完成:

@Injectable()
export class SchoolService {
  constructor(private db: AngularFirestore) {
  }

  getSchools(): Observable<School[]> {
    return this.db.collection<School>('schools').valueChanges();
  }
}

在我的组件中:

export class SchoolComponent implements OnInit {
  formControl: FormControl = new FormControl();
  schools: Observable<School[]>;
  filteredSchools: Observable<School[]>;

  constructor(private schoolService: SchoolService) {
  }

  ngOnInit() {
    this.schools = this.schoolService.getSchools();

    //Below line gives error "Type Observable<Observable<School[]>> is not assignable to type Observable<School[]>".
    this.filteredSchools = this.formControl.valueChanges.pipe(
      startWith(''),
      map(name => this.filterSchools(name))
    );
  }

  filterSchools(name: string): Observable<School[]> {
    return this.schools.map(school => school.filter(s => s.name.toLowerCase().includes(name)));
  }
}

和我的html:

<form>
  <mat-form-field>
    <input type="text" matInput placeholder="Type Your School to Continue" [matAutocomplete]="auto"
           [formControl]="formControl">
    <mat-autocomplete #auto="matAutocomplete">
      <mat-option *ngFor="let school of filteredSchools | async" [value]="school">
        <span>{{school.name}}</span> |
        <small>{{school.city}}</small>
      </mat-option>
    </mat-autocomplete>
  </mat-form-field>
</form>

中的函数 ngOnInit 给予 Type Observable<Observable<School[]>> is not assignable to type Observable<School[]> 错误我怎样才能解决这个问题?

2 回复 | 直到 8 年前

martin 8 年前

错误正好说明了问题所在。您定义了:

filteredSchools: Observable<School[]>;

但稍后您将创建一个Observable,它将发出(映射每个值)的结果 filterSchools(name: string): Observable<School[]> 它还返回一个可观察的,所以在最后你有一个可观察的 Observable<Observable<School[]>> 。

看起来你只是想 switchMap (或 mergeMap 或 concatMap )而不是 map 。 开关映射 将订阅嵌套的Observable并将链转换为 Observable<School[]> :

this.filteredSchools = this.formControl.valueChanges.pipe(
  startWith(''),
  switchMap(name => this.filterSchools(name))
);

alsami 8 年前

我建议使用 Observable.combineLatest(...)

public ngOnInit(): void {
   this.schools = this.schoolService.getSchools();

   this.filteredSchools = Observable.combineLatest(
      this.formControl.valueChanges.startWith(''),
      this.schools
   ).map(([filter, schools]) => {
       if (!filter || filter === '') {
          return schools;
       }

       return schools.filter(s => s.name.toLowerCase().includes(name));
   });
}

只有当其中一个可观测对象发出新数据时,才会触发末尾仍有冷可观测对象。

不是你的问题,但对于你的模板自动完成,你需要 displayWith 作用