c# - 我得到 NullReferenceException

Question

填充Repeater时我得到NullReferenceException。某些产品功能为空。我在使用UrlDecode（）和kill（）方法时使用了IsNullControl（）方法来避免异常。但我仍然得到错误。

   <asp:Repeater ID="rptProducts" runat="server">
        <ItemTemplate>
                <div>
                    <%# Eval("ProductName")%>
                </div>
                <div>
                    <%# kill(Server.UrlDecode(IsNullControl(Eval("ProductFeature").ToString())))%>
                </div>
        </ItemTemplate>
    </asp:Repeater>

    try
    {
        ProductsDataContext pdc = new ProductsDataContext();
        var query = from p in pdc.Products
                    select p;

        rptProducts.DataSource = query;
        rptProducts.DataBind();
    }
    catch (Exception ex)
    {
        Response.Write(ex.Message);
    }

    public static string kill(string val)
    {
        val = val.Replace("<ul>", " ");
        val = val.Replace("<li>", " ");
        val = val.Replace("</li>", "<br/>");
        val = val.Replace("</ul>", " ");
        return val.ToString();
    }

    public static string IsNullControl(string val)
    {
        string space = " ";
        if (string.IsNullOrEmpty(val))
        {
            val = space;
        }
        return space;
    }

Answer 1

在此代码片段中检查 null 之前，您首先将字段转换为字符串 -->Eval("ProductFeature").ToString()

Answer 2

检查 null 如下

<%#kill(Server.UrlDecode(Eval("ProductFeature")?? String.Empty))%>

或者您可以更改查询如下

 var query = from p in pdc.Products
             select p
             where p!= null;