title: Is it possible to extend DefaultValueAccessor?
body: <p>I am wondering if I have to implement the <code>ControlValueAccessor</code> to get the same behavior as with the <code>DefaultValueAccessor</code> for my own component or can I extend the class?</p>
  
  <p>Extending the class ends with a template parse error (yes, the component is already part of the module).</p>
  
  <p>module:</p>
  
  <pre><code>@NgModule({
      imports: [
          BrowserModule,
          HttpModule,
          FormsModule,
      ],
      declarations: [
          AppComponent ,
          DatePickerComponent,
      ],
      bootstrap:    [ AppComponent ],
  })
  export class AppModule { }
  </code></pre>
  
  <p>component:</p>
  
  <pre><code>export class DatePickerComponent extends DefaultValueAccessor {
  </code></pre>
  
  <p>error:</p>
  
  <pre><code>Unhandled Promise rejection: Template parse errors:
  'date-picker' is not a known element:
  1. If 'date-picker' is an Angular component, then verify that it is part of this module.
  2. If 'date-picker' is a Web Component then add "CUSTOM_ELEMENTS_SCHEMA" to the '@NgModule.schemas' of this component to suppress this message. ("
      &lt;div class="col-sm-7"&gt;
          &lt;div class="input-group"&gt;
              [ERROR -&gt;]&lt;date-picker [name]="beginn" [(ngModel)]="startDate"&gt;&lt;/date-picker&gt;
          &lt;/div&gt;
          &lt;p id="b"): 
  </code></pre>