Fixes #3240: Added support for assigning an anonymous function to...

Fixes #3240: Added support for assigning an anonymous function to `yii\widgets\ActiveForm::fieldConfig`

ActiveForm.php

@@ -65,6 +65,11 @@ use yii\base\InvalidConfigException;
  */
 class ActiveForm extends \yii\widgets\ActiveForm
 {
+    /**
+     * @var string the default field class name when calling [[field()]] to create a new field.
+     * @see fieldConfig
+     */
+    public $fieldClass = 'yii\bootstrap\ActiveField';
     /**
      * @var array HTML attributes for the form tag. Default is `['role' => 'form']`.
      */
@@ -91,9 +96,6 @@ class ActiveForm extends \yii\widgets\ActiveForm
         if ($this->layout !== 'default') {
             Html::addCssClass($this->options, 'form-' . $this->layout);
         }
-        if (!isset($this->fieldConfig['class'])) {
-            $this->fieldConfig['class'] = ActiveField::className();
-        }
         parent::init();
     }
 }