form代码

  $form->checkbox('nr', __('内容'))->options(['1' => 'A','2' => 'B', '3' => 'C'])->required();

grid代码

 $grid->column('nr', __('内容'))->display(function($arr){
            return implode(',', $arr); 
   });

模型代码,nr是字段，注意大小写

 public function getNrAttribute($value)
    {
        return explode(',', $value);
    }
    public function setNrAttribute($value)
    {
        $this->attributes['nr'] = implode(',', $value);
    }