角度5显示“未找到数据".如果结果为空 [英] Angular 5 show "No data found" on ngIf empty results

问题描述

我正在使用Angular 5，并且正在构建带有一些用于过滤列表的按钮的项目列表.我正在努力做的是，当其中一个过滤器隐藏列表的每一项时，显示一条找不到数据"的消息.

I'm using Angular 5 and I'm building a list of items with some buttons that filter the list. What I'm struggling to do is show a "No data found" kind of message when one of those filters hide every item of the list.

基本上是这样:

过滤器按钮

<div padding>
    <ion-segment [(ngModel)]="filter" (ionChange)="onFilterChange()">
        <ion-segment-button value="all">
            All
        </ion-segment-button>
        <ion-segment-button value="2">
            Pending
        </ion-segment-button>
        <ion-segment-button value="1">
            Confirmed
        </ion-segment-button>
    </ion-segment>
</div>

列表

<ion-list *ngFor="let r of (reservations | async)">
    <ion-card *ngIf="(filter == 'all' || filter == r.confirmed)">
        <ion-item>
            Item
        </ion-item>
    </ion-card>    
</ion-list>

注意:我使用的是异步管道，因为数据来自Firebase实时数据库.

因此，我的所有项目都处于待处理状态(已确认:2)，因此，当我单击已确认"按钮时，列表上的所有项目都被隐藏了，这是完美的.但是，如何显示找不到数据"消息而不是空列表?

So, all my items are in a state of pending (having confirmed: 2), so when I click on the Confirmed button, all the items on the list get hidden, which is perfect. But how can I show a "No data found" message instead of an empty list?

我尝试了else条件，但是我收到多条找不到数据"消息(每个隐藏项一个):

I've tried the else condition, but I'm getting multiple "No data found" messages (one for each hidden item):

<ion-list *ngFor="let r of (reservations | async)">
    <ion-card *ngIf="(filter == 'all' || filter == r.confirmed); else empty;">
        <ion-item>
            Item
        </ion-item>
    </ion-card>    
</ion-list>
<ng-template #empty>
    No data found...
</ng-template>

那么实现这一目标的正确方法是什么? 谢谢.

So what's the correct way of achieving this? Thanks.

推荐答案

IMO，您不应该显示原始保留列表.而是显示已过滤的列表:

IMO you shouldnt display the raw list of reservations. Instead, display the already filtered list:

component.html

component.html

<ion-segment [formControl]="status" (ionChange)="onFilterChange()">
    <ion-segment-button value="2">
        Pending
    </ion-segment-button>
    <ion-segment-button value="1">
        Confirmed
    </ion-segment-button>
</ion>

<div *ngIf="empty$ | async; else notEmpty">
   Nothing
</div>
<ng-template #notEmpty>
   <ion-list *ngFor="let reservation of reservations$ | async">
        <ion-card>
            <ion-item>
                Item
            </ion-item>
        </ion-card>    
    </ion-list>
</ng-template>

component.ts

component.ts

import {combineLatest} from 'rxjs/observable/combineLatest';
import {FormControl} from '@angular/forms';

status= new FormControl;
reservations$: Observable<IReservation[]>;
empty$: Observable<boolean>;

constructor(){
   this.reservations$ = combineLatest(rawReservations$,this.status.valueChanges,this._applyFilter);
  this.empty$ = this.reservations$.map(reservations => reservations.length === 0);
}

private _applyFilter(reservations: IReservation[], status: number): IReservation[]{
  let result = reservations;
  //apply filter logic
  return result;
}

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