主题：[求助]未将对象引用设置到对象的实例？

代码如下（在窗口的afterload事件中）：

Dim cmb1 As WinForm.ComboBox
cmb1 = e.Form.Controls("ComboBox1")
cmb1.ComboList = DataTables("政策外类型表").GetComboListString("政策外类型")
Dim cmb2 As WinForm.ComboBox = e.Form.Controls("ComboBox2")
Dim str As String = e.Form.Controls("ComboBox1").Value
cmb2.ComboList = DataTables("政策外类型表").GetComboListString("政策外具体类型", "政策外类型 = '" & str & "'")

出现如下错误：