title: Angular 2+: How to make drop down menu readonly (or disable) with default value and add form validation error if no default value
body: <pre><code>&lt;mat-form-field class=""&gt;
    &lt;mat-select placeholder="Lead Status" formControlName="leadStatusId" name="leadStatusId" id="leadStatusId" [formGroup]="form"
      required *appReadOnlyView&gt;
      &lt;mat-option *ngFor="let leadStatus of allLeadStatus" [value]="leadStatus?.leadStatusId"&gt;
        {{ leadStatus?.name }}
      &lt;/mat-option&gt;
    &lt;/mat-select&gt;
  &lt;/mat-form-field&gt;
  </code></pre>
  
  <p>this is my dropdown where I need to make this field readonly and set to default value. If no default value to set, it need to add form validation error.
  I know we can't add validation with disabled, but I don't know how to do it with readonly</p>