title: Cannot add a controller from List to Widget parameter
body: <p>I was trying to add a controller from a <code>List</code> to my Widget constructor like this :</p>
  <pre><code>List&lt;TextEditingController&gt; controllers = [
      TextEditingController(),
      TextEditingController(),
      TextEditingController(),
      TextEditingController()
    ];
  
  
  List&lt;Widget&gt; _cardList = [
      (InputRefNomProduit(
        label: 'Référence',
        content: 'Taper la référence',
        label2: 'Nom du produit',
        content2: '',
        label3: 'Quantité',
        content3: 'Taper la quantité',
        label4: 'Prix',
        content4: 'Taper le prix unitaire',
        fieldController: widget.controllers.first,
        fieldController2: widget.controllers[1],
        fieldController3: widget.controllers[2],
        fieldController4: widget.controllers.last,
      )),
    ];
  </code></pre>
  <p>I'm getting this error on all <code>fieldController</code> :</p>
  <pre><code>The instance member 'widget' can't be accessed in an initializer.
  </code></pre>