Fixes #848: Added hidden field for Html::activeFileInput().

framework/yii/helpers/HtmlBase.php

@@ -1049,7 +1049,10 @@ class HtmlBase
 	 */
 	public static function activeFileInput($model, $attribute, $options = array())
 	{
-		return static::activeInput('file', $model, $attribute, $options);
+		// add a hidden field so that if a model only has a file field, we can
+		// still use isset($_POST[$modelClass]) to detect if the input is submitted
+		return static::activeHiddenInput($model, $attribute, array('id' => null, 'value' => ''))
+			. static::activeInput('file', $model, $attribute, $options);
 	}
 
 	/**