通过将DropDown控件拖放到UserControl上，您不能期望UserControl自动显示其组成控件的属性.要控制组成控件的行为，您必须为UserControl创建属性并编写代码以使其按您希望的方式工作. 此 [

By dragging and dropping a DropDown control onto a UserControl, you cannot expect the UserControl to automatically show the propeties for its constituent controls. To control the behavior of constituent controls, you have to create properties for the UserControl and write code to make it work the way you want it to be. This[^] might help you to get started.

检查这两个组合框的修饰符是否设置为公共"?

Check if the modifiers for these two combobox set to ''Public'' ?