How to change Angular Material Datepicker format in run-time

OK, so I finally find a way to change the mat-date-picker format during run-time (the documentation didn't help at all).

Step #1 - Create a service that will provide the formatting.

You probable already have a service like this, if no you should create one, so you could control the date-formatting in one place.

// date-time.service
import { Injectable } from '@angular/core';
import * as moment from 'moment';

@Injectable({ providedIn: 'root' })
export class DateTimeService
{
  public getFormat(): string
  {
    return "DD-MM-YYYY"; // add you own logic here
  }
  public getLocale(): string
  {
    return "he-IL"; // add you own logic here
  }  
}

Step #2 - Create a CustomDateAdapter, that will be responsible for parsing the date during run-time

// customDateAdapter.ts
import { Injectable } from '@angular/core';
import { MomentDateAdapter } from '@angular/material-moment-adapter';
import * as moment from 'moment';
import { DateTimeService } from './date-time.service';

@Injectable()
export class CustomDateAdapter extends MomentDateAdapter
{
  constructor(private _dateTimeService: DateTimeService)
  {
    super('en-US'); // set default locale
  }

  public format(date: moment.Moment, displayFormat: string): string
  {
    const locale = this._dateTimeService.getLocale();
    const format = this._dateTimeService.getFormat();

    return date.locale(locale).format(format);
  }
}

Please Notice: That "CustomDateAdapter" is a regular class, and not a component. Although we are injecting a service to this class. To achieve this we need to add the @Injectable() decorator to the "CustomDateAdapter", and make some light changes in the app.module.ts.

Step #3 - Modify the app.module.ts to support custom formating and to allow Dependence Injection to CustomDateAdapter.

// app.module.ts
import { DateAdapter, MatNativeDateModule } from '@angular/material';
import { MatMomentDateModule } from '@angular/material-moment-adapter'
import { CustomDateAdapter } from './<some-path>/customDateAdapter';

@NgModule({
  imports:
  [
    MatNativeDateModule,
    MatMomentDateModule
  ],
  providers:
  [
    CustomDateAdapter, // so we could inject services to 'CustomDateAdapter'
    { provide: DateAdapter, useClass: CustomDateAdapter }, // Parse MatDatePicker Format
  ]
})
export class AppModule { /* ... */ }

P.S
Please notice that the code from the question (from the "demo.component.ts") isn't relevant any more.

Demo at Stackblitz

Thanks for your idea! Just for clarification. You can use non-singleton service for setting custom formatting of datepicker value. Extending your code:

import { Injectable } from '@angular/core';
    @Injectable({ providedIn: 'root' })
    export class DateTimeService {
        private _format = 'DD.MM.YYYY';

        set format(value: string) {
            this._format = value;
        }

        public getFormat(): string {
            return this._format;
        }

        public getLocale(): string {
            return 'ru-ru';
        }
    }

If you inject this service like this:

providers: [
        { provide: MAT_DATE_LOCALE, useValue: 'ru-ru' },
        CustomDateAdapter,
        DateTimeService,
        { provide: DateAdapter, useClass: CustomDateAdapter, deps: [DateTimeService] }
]

you can store any value from your component during component working.

constructor(private dateTimeService: DateTimeService) {
    }

    ngOnInit() {
        this.dateTimeService.format = this.format;
    }