如何在使用响应数据之前调用方法?

要获取数据,您需要路由参数和类,这看起来是 combineLatest :

ngOnInit() {
    combineLatest(this.route.params, this.classService.getAllClasses())
    .subscribe(([params, classes]) => {
        if (params['id']) {
            let a = getData(classes, params['id']);
        }
    });
}

我认为你应该这样做:

    public classes: any;

    ngOnInit() {
    this.loadClasses().subscribe(() => getData());

    private getData(): void {
        this.route.params.subscribe(params => {
          if (params['id']) {
            let a = getData(this.classes, params['id']);// Notice here
          }
        });
    }

     public loadClasses(): void {
        this.classService.getAllClasses()
          .subscribe(data => {
             this.classes = data;
        });
    }