title: context.select isn't defined for BuildContext
body: <p>Why I can't use any extension methods of Provider (<code>context.select</code>, <code>context.read</code> and <code>context.listen</code>)?</p>
  <p>I get a static error like this.</p>
  <blockquote>
  <p>The method 'select' isn't defined for the type 'BuildContext'.Try
  correcting the name to the name of an existing method, or defining a
  method named 'select'..</p>
  </blockquote>
  <pre><code>class MyWidget extends StatelessWidget {
    
  
    @override
    Widget build(BuildContext context) {
  
      // Following line causes the problem
      var isFavorite = context.select&lt;FavModel, bool&gt;(
        (fav) =&gt; fav.items.contains(item),
      );
  
      return OtherWidget(...);
    }
  }
  </code></pre>