主题：控件事件代码报错

我在窗体afterload 事件中写入代码
Dim ccdd As WinForm.ComboBox = e.Form.Controls("出差地点")
Dim a As List(of String) = DataTables("地区信息").GetUniqueValues("","省级")
Dim s As List(of String) = DataTables("地区信息").GetUniqueValues("","市级")
Dim d As List(of String) = DataTables("地区信息").GetUniqueValues("","县级")
For Each q As String In a
For Each w As String In s
For Each r As String In d
 ccdd.ComboList =q & w & r
Next
Next
Next
目的就是让这个控件点击的时候可以接收到我的连接三列数据以｜分割

系统报错为类型不符

请高手指点