Google Firebase提取数据的本地过滤

Question

我正在尝试对从Firebase提取的数据进行一些过滤。

我试图通过获取完整数据并使用HTML中的 ngIf 进行过滤来做到这一点。

这是我的 public abstract class A<T, TB, C, D> where T : class where C : FooParameter where D : FooResponse where TB : B<C,D> { public TB B { get; set; } public A() { //instantiate B property } } 文件

list.ts

您看到的是在这里获取数据

import { Component, OnInit, OnDestroy } from '@angular/core';
import { DressService, Dress, City } from '../services/dress.service';
import { LanguageService } from '../services/language.service';
import { AuthService } from '../services/auth.service';
import { Router } from '@angular/router';
import { Subscription } from 'rxjs';

@Component({
    selector: 'app-list',
    templateUrl: 'list.page.html',
    styleUrls: ['list.page.scss']
})
export class ListPage implements OnInit, OnDestroy{
    dress: Dress[];
    mySub: Subscription;
    needApproval = null;
    currentCity = 'all';
    city: City[];
    citySub: Subscription;
    constructor(private dressService: DressService,
                public languageService: LanguageService,
                private authService: AuthService,
                private router: Router,
    ) {    }

    ngOnDestroy() {
        this.mySub.unsubscribe();
        this.citySub.unsubscribe();
        this.needApproval = null;
        console.log('list page destroyed');
        // tslint:disable-next-line: forin
        for (const member in this.dress) { delete this.dress[member]; }
    }
    changeFilter() {
        console.log(this.currentCity);
    }

    ngOnInit() {
        console.log('starting list page');
        this.mySub = this.dressService.getDresses().subscribe(res => {
            this.dress = res;
            console.log(typeof (this.dress));
            for (const key in this.dress) {
                if (this.dress.hasOwnProperty(key)) {
                    if (!this.dress[key].active) {
                        const currentNeedApproval = this.needApproval;
                        const addedNeedApproval = 1;
                        const newNeedApproval = Number(currentNeedApproval) + Number(addedNeedApproval);
                        this.needApproval = newNeedApproval;
                    }
                }
            }
        });
        this.gettingData();
    }

    getCurrentUser() {
        return this.authService.userDetails();
    }
    getCurrentLanguage() {
        return this.languageService.getCurrentLanguage();
    }

    changeToArabic() {
        this.languageService.changeToArabic();
    }

    changeToEnglish() {
        this.languageService.changeToEnglish();
    }
    gettingData() {
        this.citySub = this.dressService.getCities().subscribe(res => {
            this.city = res;
            console.log(this.city);
        });
    }
}

然后将其添加到要在我的HTML文件中使用的变量中

这是我的HTML文件：

        this.mySub = this.dressService.getDresses().subscribe(res => {
            this.dress = res;

我这里有一个选择菜单，该菜单从添加到项目详细信息的同一源获取数据，然后我使用ngIf条件过滤查看的项目。

一旦我更换了城市，它什么也没显示。