c# - 如果 Eval 不为空，如何在 GridView 中有选择地显示按钮？

Question

我有以下 GridView 和 ObjectDataSource:

<asp:GridView 
    ID="grdTrades" 
    runat="server" 

    DataSourceID="srcTrades" 
    DataKeyNames="tradeId"
    EnablePersistedSelection="true"            
    SelectedRowStyle-BackColor="Yellow" 
    AllowPaging="true" 
    AllowSorting="true"
    PageSize = "10" 
    AutoGenerateColumns="false" 
    >
    <Columns>
        <asp:CommandField ShowSelectButton="true" ButtonType="Link" SelectText="Select" />                           
        <asp:BoundField DataField="tradeId" HeaderText="TradeId"  ReadOnly="True" SortExpression="tradeId" />
        <asp:BoundField DataField="symbol" HeaderText="Pair" SortExpression="symbol" />
        <asp:BoundField DataField="chartTimeFrame" HeaderText="TF" SortExpression="chartTimeFrame" />
        <asp:BoundField DataField="tradeSetupId" HeaderText="Setup" SortExpression="tradeSetupId" />
        <asp:BoundField DataField="tradeType" HeaderText="Trade Type" SortExpression="tradeType" />
        <asp:BoundField DataField="side" HeaderText="Side"  ReadOnly="True" SortExpression="side" />
        <asp:BoundField DataField="units" HeaderText="Units"  ReadOnly="True" SortExpression="units" />
        <asp:BoundField DataField="price" HeaderText="Price" SortExpression="price" />
        <asp:BoundField DataField="orderDateTime" HeaderText="Order Date/Time" SortExpression="orderDateTime" />
        <asp:BoundField DataField="pipsProfit" HeaderText="Pips profit" DataFormatString="{0:F1}" SortExpression="pipsProfit" />
        <asp:BoundField DataField="riskPips" HeaderText="Pips risked" DataFormatString="{0:F1}" SortExpression="riskPips" />
        <asp:BoundField DataField="pipsInMove" HeaderText="Pips in move" DataFormatString="{0:F1}" SortExpression="pipsInMove" />
        <asp:BoundField DataField="rewardRiskRatio" HeaderText="R/R" DataFormatString="{0:F1}" SortExpression="rewardRiskRatio" />            
        <asp:BoundField DataField="pctAccountRisked" HeaderText="% risk" DataFormatString="{0:F1}" ReadOnly="True" SortExpression="pctAccountRisked" />
        <asp:BoundField DataField="pctAccountChange" HeaderText="% AcctChange" DataFormatString="{0:F2}" SortExpression="pctAccountChange" />            
        <asp:TemplateField>
            <ItemTemplate>
                <input type="button" size="x-small" value="View" onclick="javascript:ShowImageInNewPage('DisplayImage.aspx?screenshotId=<%# Eval("screenshotId") %>');" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:HyperLinkField 
            Text="Edit"
            DataNavigateUrlFields="tradeId" 
            DataNavigateUrlFormatString="EditTrade.aspx?screenshotId={0}" />                
        <CustomControls:DeleteButtonField ConfirmText="Delete this trade?" Text="Del" />
    </Columns>
</asp:GridView>

<CustomControls:CustomObjectDataSource
    id="srcTrades" 
    TypeName="DatabaseComponent.DBUtil" 
    SelectMethod="GetTrades" 
    DeleteMethod="DeleteTrade"             
    runat="server">
    <DeleteParameters>
        <asp:ControlParameter Name="tradeId" ControlId="grdTrades" PropertyName="SelectedValue"  />
    </DeleteParameters> 
</CustomControls:CustomObjectDataSource>  

在我的 TemplateField 中，如果 screenshotId 的计算结果为非空非零值，我只想显示按钮。如果 screenshotId 是 DbNull 或 0，那么我想将该单元格留空。我应该在哪里编写代码，在 ASP.NET 代码中，还是必须编写一些代码隐藏？什么是最好的方法？

更新

我添加了以下代码:

protected void grdTrades_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        var dataitem = DataBinder.Eval(e.Row.DataItem, "screenshotId");
        Button btnShowImage = e.Row.FindControl("btnShowImage") as Button;
        if (dataItem.screenshotId != null && screenshotId > 0)
        {
            btnShowImage.OnClientClick = "javascript:ShowImageInNewPage(\"DisplayImage.aspx?screenshotId=" + dataItem.screenshotId + "\");";
            btnShowImage.Visible = true;
        }
        else
            btnShowImage.Visible = false;                
    }
}  

但是我得到了这些错误:

The name 'dataItem' does not exist in the current context

和

The name 'screenshotId' does not exist in the current context

MyRow 也没有被识别。有什么想法吗？

更新 2

我终于解决了 - 这是我的代码:

protected void grdTrades_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        // If you do it like this, you already get the screenshotId value;
        var screenshotId = DataBinder.Eval(e.Row.DataItem, "screenshotId");
        Response.Write("ScreenshotId: " + screenshotId.ToString());

        Button btnShowImage = e.Row.FindControl("btnShowImage") as Button;

        if (screenshotId is System.DBNull)
            btnShowImage.Visible = false;
        else            
        {
            btnShowImage.Text = screenshotId.ToString();
            btnShowImage.OnClientClick =
               "javascript:ShowImageInNewPage(\"DisplayImage.aspx?screenshotId=" + screenshotId.ToString() + "\");";
            btnShowImage.Visible = true;
        }            
    }
}

Answer 1

你能以声明的方式完成这一切吗？

    <asp:TemplateField>
        <ItemTemplate>
                <input runat="server" visible='<%# Eval("screenshotId") != DBNull.Value %>' type="button" size="x-small" value="View" onclick='<%# "ShowImageInNewPage(\"DisplayImage.aspx?screenshotId=" + Eval("screenshotId") + "\")" %>' />
        </ItemTemplate>
    </asp:TemplateField>