主题：窗口列表项目排除空值

请DX帮我看看，窗口组合框列表项目怎么不能排除空置，我代码哪里有问题，谢谢。
Dim cmb As WinForm.ComboBox = e.form.Controls("精度")
cmb.ComboList = DataTables("基础表").GetComboListString("精度","精度 = 'IsNot Nothing'")
Dim cmb3 As WinForm.ComboBox = e.form.Controls("装夹难度")
cmb3.ComboList = DataTables("基础表").GetComboListString("装夹","装夹 = 'IsNot Nothing'")
Dim cmb1 As WinForm.ComboBox = e.form.Controls("钢性")
cmb1.ComboList = DataTables("基础表").GetComboListString("钢性","钢性 = 'IsNot Nothing'")

还是不行我两种都试了：
第一种：
Dim cmb As WinForm.ComboBox = e.form.Controls("精度")
cmb.ComboList = DataTables("基础表").GetComboListString("精度","精度 = 'Is Not Null '")
Dim cmb3 As WinForm.ComboBox = e.form.Controls("装夹难度")
cmb3.ComboList = DataTables("基础表").GetComboListString("装夹","装夹 = 'Is Not Null '")
Dim cmb1 As WinForm.ComboBox = e.form.Controls("钢性")
cmb1.ComboList = DataTables("基础表").GetComboListString("钢性","钢性 = 'Is Not Null '")
第二种：
Dim cmb As WinForm.ComboBox = e.form.Controls("精度")
cmb.ComboList = DataTables("基础表").GetComboListString("精度","精度 Is Not Null ")
Dim cmb3 As WinForm.ComboBox = e.form.Controls("装夹难度")
cmb3.ComboList = DataTables("基础表").GetComboListString("装夹","装夹 Is Not Null ")
Dim cmb1 As WinForm.ComboBox = e.form.Controls("钢性")
cmb1.ComboList = DataTables("基础表").GetComboListString("钢性","钢性 Is Not Null ")

我这样也是过了，也是不行：
Dim cmb As WinForm.ComboBox = e.form.Controls("精度")
cmb.ComboList = DataTables("基础表").GetComboListString("精度")
Dim cmb3 As WinForm.ComboBox = e.form.Controls("装夹难度")
cmb3.ComboList = DataTables("基础表").GetComboListString("装夹 ")
Dim cmb1 As WinForm.ComboBox = e.form.Controls("钢性")
cmb1.ComboList = DataTables("基础表").GetComboListString("钢性")

我是用5楼代码的结果，好像3个代码都会一样的结果，请看图片：

此主题相关图片如下：打开窗口时报错图片.bmp



此主题相关图片如下：点确定能打开窗口，请看精度下拉项目.bmp

精度列是字符型，结果一样的，在表中属性PrepareEdit事件中设置能正常使用，但我现在想做成窗口录入。
If e.IsFocusCell Then
    If e.Col.Name = "难度情况_精度" Then
        e.Col.Combolist = DataTables("基础表").GetComboListString("精度")
    End If
    If e.Col.Name = "难度情况_切削" Then
        e.Col.Combolist = DataTables("基础表").GetComboListString("切削")
    End If
    If e.Col.Name = "难度情况_装夹" Then
        e.Col.Combolist = DataTables("基础表").GetComboListString("装夹")
    End If
    If e.Col.Name = "难度情况_钢性" Then
        e.Col.Combolist = DataTables("基础表").GetComboListString("钢性")
    End If
    If e.Col.Name = "工序_班组" Then
        e.Col.Combolist = DataTables("基础表").GetComboListString("班组")
    End If
    If e.Col.Name = "工艺_工作中心组" Then
        e.Col.Combolist = DataTables("基础表").GetComboListString("工作中心组","[班组] = '" & e.Row("工序_班组") & "'")
    End If
End If

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点击浏览该文件:铣床产品工艺录入.rar

呵呵，可能是我昨天刚开始代码出错，就改成在控件属性中设置来源于数据表了，忘了改回来，谢谢C版