How do I implement autocomplete in a <mat-select> component?

Question

I would like to combine the autocomplete feature with a multiselect mat-select chooser because the optionslist will be quite long.

I've already searched on stackoverflow for the answer and the closest to an answer was this implement a search filter for the <mat-select> component of angular material

However the examples are about table and not mat-select.

My question is, is it possible to add the autocomplete feature to mat-select. And if not could i make an autocomplete that includes checkboxes in front of each item in the list?

Thank you

EDIT: I've found out that primefaces for angular does have a multiselect list that allows you to search for listitems. It also includes a builtin select-all button! You can find it here https://www.primefaces.org/primeng/#/multiselect

You can install primefaces with npm install primeng --save

Answer 1

You can implement an autocomplete multi-select using MatAutocomplete and some tricks. I'm fairly sure you can't do it with MatSelect since that doesn't give you control over the input element. The technique is a little odd, but it works fine. The idea is to manage selections in your controller, and set the "value" of each mat-option to the same thing - your selected options. You also need to trap clicks to allow users to interact with the list (rather than have it close immediately when clicked), and of course provide checkboxes inside the mat-option items. A few other tricks are necessary as well - here is a quick and dirty example that shows what to do.

HTML:

<mat-form-field class="example-full-width">
    <input type="text" placeholder="Select Users" aria-label="Select Users" matInput [matAutocomplete]="auto" [formControl]="userControl">
    <mat-hint>Enter text to find users by name</mat-hint>
</mat-form-field>

<mat-autocomplete #auto="matAutocomplete" [displayWith]="displayFn">
    <mat-option *ngFor="let user of filteredUsers | async" [value]="selectedUsers">
        <div (click)="optionClicked($event, user)">
            <mat-checkbox [checked]="user.selected" (change)="toggleSelection(user)" (click)="$event.stopPropagation()">
                {{ user.firstname }} {{ user.lastname }}
            </mat-checkbox>
        </div>
    </mat-option>
</mat-autocomplete>

<br><br>

<label>Selected Users:</label>
<mat-list dense>
    <mat-list-item *ngIf="selectedUsers?.length === 0">(None)</mat-list-item>
    <mat-list-item *ngFor="let user of selectedUsers">
        {{ user.firstname }} {{ user.lastname }}
    </mat-list-item>
</mat-list>

TS:

import { Component, OnInit, ViewChild } from '@angular/core';
import { FormControl } from '@angular/forms';
import { Observable } from 'rxjs';
import { map, startWith } from 'rxjs/operators';

export class User {
  constructor(public firstname: string, public lastname: string, public selected?: boolean) {
    if (selected === undefined) selected = false;
  }
}

/**
 * @title Multi-select autocomplete
 */
@Component({
  selector: 'multiselect-autocomplete-example',
  templateUrl: 'multiselect-autocomplete-example.html',
  styleUrls: ['multiselect-autocomplete-example.css']
})
export class MultiselectAutocompleteExample implements OnInit {

  userControl = new FormControl();

  users = [
    new User('Misha', 'Arnold'),
    new User('Felix', 'Godines'),
    new User('Odessa', 'Thorton'),
    new User('Julianne', 'Gills'),
    new User('Virgil', 'Hommel'),
    new User('Justa', 'Betts'),
    new User('Keely', 'Millington'),
    new User('Blanca', 'Winzer'),
    new User('Alejandrina', 'Pallas'),
    new User('Rosy', 'Tippins'),
    new User('Winona', 'Kerrick'),
    new User('Reynaldo', 'Orchard'),
    new User('Shawn', 'Counce'),
    new User('Shemeka', 'Wittner'),
    new User('Sheila', 'Sak'),
    new User('Zola', 'Rodas'),
    new User('Dena', 'Heilman'),
    new User('Concepcion', 'Pickrell'),
    new User('Marylynn', 'Berthiaume'),
    new User('Howard', 'Lipton'),
    new User('Maxine', 'Amon'),
    new User('Iliana', 'Steck'),
    new User('Laverna', 'Cessna'),
    new User('Brittany', 'Rosch'),
    new User('Esteban', 'Ohlinger'),
    new User('Myron', 'Cotner'),
    new User('Geri', 'Donner'),
    new User('Minna', 'Ryckman'),
    new User('Yi', 'Grieco'),
    new User('Lloyd', 'Sneed'),
    new User('Marquis', 'Willmon'),
    new User('Lupita', 'Mattern'),
    new User('Fernande', 'Shirk'),
    new User('Eloise', 'Mccaffrey'),
    new User('Abram', 'Hatter'),
    new User('Karisa', 'Milera'),
    new User('Bailey', 'Eno'),
    new User('Juliane', 'Sinclair'),
    new User('Giselle', 'Labuda'),
    new User('Chelsie', 'Hy'),
    new User('Catina', 'Wohlers'),
    new User('Edris', 'Liberto'),
    new User('Harry', 'Dossett'),
    new User('Yasmin', 'Bohl'),
    new User('Cheyenne', 'Ostlund'),
    new User('Joannie', 'Greenley'),
    new User('Sherril', 'Colin'),
    new User('Mariann', 'Frasca'),
    new User('Sena', 'Henningsen'),
    new User('Cami', 'Ringo')
  ];

  selectedUsers: User[] = new Array<User>();

  filteredUsers: Observable<User[]>;
  lastFilter: string = '';

  ngOnInit() {
    this.filteredUsers = this.userControl.valueChanges.pipe(
      startWith<string | User[]>(''),
      map(value => typeof value === 'string' ? value : this.lastFilter),
      map(filter => this.filter(filter))
    );
  }

  filter(filter: string): User[] {
    this.lastFilter = filter;
    if (filter) {
      return this.users.filter(option => {
        return option.firstname.toLowerCase().indexOf(filter.toLowerCase()) >= 0
          || option.lastname.toLowerCase().indexOf(filter.toLowerCase()) >= 0;
      })
    } else {
      return this.users.slice();
    }
  }

  displayFn(value: User[] | string): string | undefined {
    let displayValue: string;
    if (Array.isArray(value)) {
      value.forEach((user, index) => {
        if (index === 0) {
          displayValue = user.firstname + ' ' + user.lastname;
        } else {
          displayValue += ', ' + user.firstname + ' ' + user.lastname;
        }
      });
    } else {
      displayValue = value;
    }
    return displayValue;
  }

  optionClicked(event: Event, user: User) {
    event.stopPropagation();
    this.toggleSelection(user);
  }

  toggleSelection(user: User) {
    user.selected = !user.selected;
    if (user.selected) {
      this.selectedUsers.push(user);
    } else {
      const i = this.selectedUsers.findIndex(value => value.firstname === user.firstname && value.lastname === user.lastname);
      this.selectedUsers.splice(i, 1);
    }

    this.userControl.setValue(this.selectedUsers);
  }

}