Angular ngx-mat-select-search Custom Component

I am trying to use the ngx-mat-select-search component to put a mat-select style dropdown menu with a search bar in my application. https://www.npmjs.com/package/ngx-mat-select-search

I have the dropdown working fine, but I am trying to turn it into a custom directive that I can then call and reuse on multiple pages through out the app.

So far I have this: site-dropdown-component.ts

import {AfterViewInit, Component, OnDestroy, OnInit, ViewChild} from '@angular/core';
import {FormControl} from '@angular/forms';
import {ReplaySubject, Subject} from 'rxjs';
import {MatSelect} from '@angular/material';
import {take, takeUntil} from 'rxjs/operators';

@Component({
  selector: 'app-site-dropdown',
  template: `
    <mat-form-field class="w-100">
      <mat-select [formControl]="siteCtrl" placeholder="Site" #singleSelect>
        <mat-option>
          <ngx-mat-select-search [formControl]="siteFilterCtrl" [placeholderLabel]="'Search Sites...'"></ngx-mat-select-search>
        </mat-option>
        <mat-option *ngFor="let site of filteredSites | async" [value]="site">{{site.name}}</mat-option>
      </mat-select>
    </mat-form-field>
  `
})
export class SiteDropdownComponent implements OnInit, OnDestroy, AfterViewInit {
  /** list of sites */
  protected sites: Site[] = SITES;

  /** control for the selected site */
  public siteCtrl: FormControl = new FormControl();

  /** control for the MatSelect filter keyword */
  public siteFilterCtrl: FormControl = new FormControl();

  /** list of sites filtered by search keyword */
  public filteredSites: ReplaySubject<Site[]> = new ReplaySubject<Site[]>(1);

  @ViewChild('singleSelect') singleSelect: MatSelect;

  /** Subject that emits when the component has been destroyed. */
  protected onDestroy = new Subject<void>();
  constructor() { }

  ngOnInit(): void {
    // set initial selection
    this.siteCtrl.setValue(this.sites);
    // load the initial site list
    this.filteredSites.next(this.sites.slice());
    // listen for search field value changes
    this.siteFilterCtrl.valueChanges
      .pipe(takeUntil(this.onDestroy))
      .subscribe(() => {
        this.filterSites();
      });
  }

  ngAfterViewInit(): void {
    this.setInitialValue();
  }

  ngOnDestroy(): void {
    this.onDestroy.next();
    this.onDestroy.complete();
  }

  /**
   * Sets the initial value after the filteredBanks are loaded initially
   */
  protected setInitialValue() {
    this.filteredSites
      .pipe(take(1), takeUntil(this.onDestroy))
      .subscribe(() => {
        // setting the compareWith property to a comparison function
        // triggers initializing the selection according to the initial value of
        // the form control (i.e. _initializeSelection())
        // this needs to be done after the filteredBanks are loaded initially
        // and after the mat-option elements are available
        this.singleSelect.compareWith = (a: Site, b: Site) => a && b && a.id === b.id;
      });
  }

  protected filterSites() {
    if (!this.sites) {
      return;
    }
    // get the search keyword
    let search = this.siteFilterCtrl.value;
    if (!search) {
      this.filteredSites.next(this.sites.slice());
      return;
    } else {
      search = search.toLowerCase();
    }
    // filter the sites
    this.filteredSites.next(
      this.sites.filter(site => site.name.toLowerCase().indexOf(search) > -1)
    );
  }
}


export interface Site {
  id: string;
  name: string;
}

export const SITES: Site[] = [
  {id: 'site1', name: 'Site 1'},
  {id: 'site2', name: 'Site 2'},
  {id: 'site3', name: 'Site 3'},
];

For the component im trying to use it in, i have:

<app-site-dropdown formControlName="site"></app-site-dropdown>

And inside the component class I have a form:

this.mySearchForm = this.formBuilder.group( {
  site: []
});

I can see and interact with the dropdown just fine, but when i submit my form, I cannot get the value of the selected option. It just always returns null when i try mySearchForm.controls['site'].value

What am I missing to be able to inject my custom dropdown component, and retrieve its value upon form submission?

UPDATE:

I was able to make it work by doing the following:

Inside site-dropdown.component.ts, I changed

protected siteCtrl: FormControl;

@Input() siteCtrl: FormControl;

And inside my html using the custom dropdown, i added:

<app-site-dropdown [siteCtrl]="myForm.get('site')"></app-site-dropdown>

This allowed me to save the selected value into my form on submission.

you can get the value of the selected option by having your SiteDropdownComponent implement the ControlValueAccessor interface as follows, resulting in your SiteDropdownComponent behaving as a form control and allowing to access the value with e.g. <app-site-dropdown formControlName="site"></app-site-dropdown>:

...
import { forwardRef } from '@angular/core';
import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';

@Component({
  selector: 'app-site-dropdown',
  template: ...
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => SiteDropdownComponent),
      multi: true
    }
  ],
})
export class SiteDropdownComponent implements OnInit, OnDestroy, AfterViewInit, ControlValueAccessor {
  ...

  onChange: Function = (_: any) => {};
  onTouched: Function = (_: any) => {};

  constructor() { }

  ngOnInit() {
    ...
    // call this.onChange to notify the parent component that the value has changed
    this.siteCtrl.valueChanges
      .pipe(takeUntil(this.onDestroy))
      .subscribe(value => this.onChange(value))
  }

  writeValue(value: string) {
    // set the value of siteCtrl when the value is set from outside the component
    this.siteCtrl.setValue(value);
  }

  registerOnChange(fn: Function) {
    this.onChange = fn;
  }

  registerOnTouched(fn: Function) {
    this.onTouched = fn;
  }

}

See e.g. https://github.com/bithost-gmbh/ngx-mat-select-search/blob/d7ea78d511bbec45143c58c855f013a44d0d5055/src/app/mat-select-search/mat-select-search.component.ts#L134