iOS8 Swift：如何访问/编辑/删除默认/私有inputAccessoryView高度约束'_UIKBAutolayoutHeightConstraint'

我想使inputAccessoryView随着UITextView内部的增长而扩展。inputAccessoryView具有一个私有NSLayoutConstraint，其标识符为“ _UIKBAutolayoutHeightConstraint”

尽管经历了inputAccessoryView.constraints数组中的每个约束，但我还是无法访问。我尝试了两种方法：

 var constraints:[NSLayoutConstraint] = tableView.inputAccessoryView!.constraints() as Array
        for  (c: NSLayoutConstraint) in constraints{
            if c.identifier == "_UIKBAutolayoutHeightConstraint"{
                println("height")
            }
        }



var constraints:[NSLayoutConstraint] = tableView.inputAccessoryView!.constraints() as Array
        for  (c: NSLayoutConstraint) in constraints{
            if c.firstAttribute == NSLayoutAttribute.Height{
                println("height constraint found")
            }
        }