角度4 * ng用于带有管道的数组长度

Question

I have a range slider in my app. If you drag the range slider, based on "sliderPipe" change results will appear. My problem is I'm unable to display the "No Records Found" message.

html template

<div class="well" *ngFor="let data of onewayFormData$ | 
                                  sliderPipe: sliderValue as results;">
  <div class="row">
    <div class="col-md-6 onewayresults">
      <h2> {{ data.cost | currency: 'INR':true }} </h2>
      <h3> {{ data.agencycode }} </h3>
      <h5> {{ data.ocity }} > {{ data.dcity }}</h5>
      <h5> Depart: {{ data.depart }} </h5>
      <h5> Arrive: {{ data.arrive }} </h5>
    </div>
    <div class="col-md-6">
      <div style="float:right;">
        <img [src]="data.imageurl" width="120px" height="100px" [alt]="data.agency" />
        <br/>
        <br/>
        <button class="btn btn-success"> Book Tickets </button>
      </div>
    </div>
  </div>
  Length: {{ results }}
  <div class="well" *ngIf="results.length == ''">
    <div class="alert alert-danger"> No Results Found....... </div>
  </div>
</div>

Pipe Code

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'sliderPipe'
})
export class SliderPipePipe implements PipeTransform {
  transform(value, args ? ) { // ES6 array destructuring
  console.log('Arguments: ' , value.length);
  return value.filter(data => {
      return data.cost >= args;
    });
  }
}

Answer 1

If results is an array:

The length of an array is always of type number , so you need to check against results.length == 0 for an empty array.

If results is of type number:

Check against results == 0 .