iOS-Cannot find interface declaration for 'XX', superclass of 'XX'

构建一个父类，然后创建一个子类继承于父类，报错如下：

Cannot find interface declaration for 'BillSwitchGoodsViewModel', superclass of 'SaleBillSwitchGoodsViewModel'
Class 'SaleBillSwitchGoodsViewModel' defined without specifying a base class

其实就是子类找不到父类导致的，只需要在子文件中import父类即可，如下：