角材质选择多个显示值

Question

Is it possible to change displayed value in Angular Material multiple select? How can I do this eg Products:(0/12) depends on number of selected items.

Answer 1

Use a <mat-select-trigger> for that. For example:

<mat-form-field>
  <mat-select placeholder="Toppings" [formControl]="toppings" multiple>
    <mat-select-trigger>
      {{toppings.value ? toppings.value[0] : ''}}
      <span *ngIf="toppings.value?.length > 1" class="example-additional-selection">
        (+{{toppings.value.length - 1}} {{toppings.value?.length === 2 ? 'other' : 'others'}})
      </span>
    </mat-select-trigger>
    <mat-option *ngFor="let topping of toppingList" [value]="topping">{{topping}}</mat-option>
  </mat-select>
</mat-form-field>

See the demo here: https://stackblitz.com/angular/qkjbojyxebly?file=app%2Fselect-custom-trigger-example.html

Answer 2

In addition to the answer above, to set the selection to an initial value, this is how you'd extend select-custom-trigger-example.ts in the given stackblitz demo:

import {Component, OnInit} from '@angular/core';
import {FormControl} from '@angular/forms';

/** @title Select with custom trigger text */
@Component({
  selector: 'select-custom-trigger-example',
  templateUrl: 'select-custom-trigger-example.html',
  styleUrls: ['select-custom-trigger-example.css'],
})
export class SelectCustomTriggerExample implements OnInit {
  toppings = new FormControl();

  toppingList: string[] = ['Extra cheese', 'Mushroom', 'Onion', 'Pepperoni', 'Sausage', 'Tomato'];

  ngOnInit()
  {
    // initalSelection could be the result from a service call (database, backend, etc.):
    let initalSelection : string [] = ["Onion","Pepperoni","Sausage"];

    // set initalSelection as inital value:
    this.toppings.setValue(initalSelection);
  }
}