ASP VB.net在页面加载时根据其值隐藏详细信息视图

Question

我想在页面加载中隐藏Detailsview控件，其中控件值为0。Detailsview链接到sql数据库，显示的值是从零开始的数字值。

我将控件设置如下：

<asp:DetailsView Height="25px" Width="60px" ID="dv2cG" runat="server" AutoGenerateRows="False" DataSourceID="ds2cG" BorderWidth="0px" HorizontalAlign="Center" BackColor="#ccd0ff" >
    <Fields>
        <asp:BoundField showheader="false" DataField="2cG" HeaderText="2cG" ReadOnly="True" SortExpression="2cG" />
    </Fields>
</asp:DetailsView>

<asp:SqlDataSource ID="ds2cG" runat="server" ConnectionString="<%$ ConnectionStrings:MaltingsConnectionString %>" SelectCommand="select sum(case when (name = 'English' and ks2en = '2c' and result like 'G') or (name = 'Mathematics' and ks2ma = '2c' and result like 'G') or (not name = 'Mathematics' and not name = 'English' and ks2av = '2c' and result like 'G') then 1 else 0 end) as '2cG' from student join subject on student.upn=subject.upn where @TeachingGroup = 'Select All' AND ([StuYear] = @StuYear) AND ([DataCollection] = @DataCollection) AND ([Name] = @SubjectName) OR @TeachingGroup &lt;&gt; 'Select All' AND ([StuYear] = @StuYear) AND ([DataCollection] = @DataCollection) AND ([Name] = @SubjectName) AND ([TeachingGroup] = @TeachingGroup)">

<SelectParameters>
    <asp:ControlParameter ControlID="DdlTeachingGroup" Name="TeachingGroup" PropertyName="SelectedValue" />
    <asp:ControlParameter ControlID="DdlYear" Name="StuYear" PropertyName="SelectedValue" />
    <asp:ControlParameter ControlID="ddlDataCollection" Name="DataCollection" PropertyName="SelectedValue" />
    <asp:ControlParameter ControlID="DdlSubject" Name="SubjectName" PropertyName="SelectedValue" />
 </SelectParameters>

我编写了以下简单过程：

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    'G column - sets dataitem to visible false where the dataitem equal 0
     If dv2cG.DataItem = 0 Then
         dv2cG.Visible = False
     Else
         dv2cG.Visible = True
     End If

End Sub

这将成功隐藏DetailsView。 但是，即使控件中的值不等于1，也会这样做。

谢谢阅读。

Answer 1

我在这里踩到这篇文章时解决了这个问题 。

我在sql命令上使用了nullif()函数，例如

select nullif(sum(case when.....then 1 else 0 end),0) as '2cG'