title: Checkbox angular material checked by default
body: <p>I am trying to use an Angular Material checkbox, and set it by default as checked, but it is displayed as non-checked, what is wrong?</p>
  
  <pre><code>&lt;mat-checkbox class = "example-margin" [(ngModel)] = obj.impresora&gt; 
       &lt;label&gt;Printer&lt;/label&gt; 
  &lt;/mat-checkbox&gt;
  </code></pre>
  
  <p>obj.impresora property is boolean</p>