主题：窗口中数值复合框不可以相互运算吗

Dim htsl As WinForm.NumericComboBox = e.Form.Controls("NumericComboBox1")
Dim htdj As WinForm.NumericComboBox = e.Form.Controls("NumericComboBox2")
Dim htze As WinForm.Label = e.Form.Controls("Label8")
If htsl.value IsNot Nothing And htdj.value IsNot Nothing Then
htze.value = htdj.value * htsl.value
End If

这样会报错，那正确的应该怎么样呢？