Question

我在网格视图中的页脚中有一个下拉列表。我希望它从数据库中读取，因为这是用于插入。

我从here获得了一个用于此目的的代码并且它可以正常工作，但是当我为页脚编写相同内容时它会给出错误：System.NullReferenceException。

我的代码如下：

 <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" OnRowDataBound="OnRowDataBound" ShowFooter="True">
    <Columns>
        <asp:BoundField HeaderText="EId" DataField="EId" />
        <asp:TemplateField HeaderText = "CName">
            <ItemTemplate>
                <asp:Label ID="lblCountry" runat="server" Text='<%# Eval("CName") %>' Visible = "false" />
                <asp:DropDownList ID="ddlCountries" runat="server">
                </asp:DropDownList>

            </ItemTemplate>
             <FooterTemplate>

              <asp:DropDownList ID="ddlCName"  CssClass="auto-style16" Width="80px" runat="server" ></asp:DropDownList>


        </FooterTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

代码背后的代码：

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            GridView1.DataSource = GetData("select * from TbExam inner join TBCourse on TBCourse.CId = TbExam.CId inner join TbCourseMajor on TbCourseMajor.CId=TBCourse.CId");
            GridView1.DataBind();
        }
    }

    private DataSet GetData(string query)
    {
        string conString = ConfigurationManager.ConnectionStrings["RigesterConnectionString1"].ConnectionString;

    SqlCommand cmd = new SqlCommand(query);
        using (SqlConnection con = new SqlConnection(conString))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataSet ds = new DataSet())
                {
                    sda.Fill(ds);
                    return ds;
                }
            }
        }
    }

    protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            //Find the DropDownList in the Row
            DropDownList ddlCountries = (e.Row.FindControl("ddlCountries") as DropDownList);
            ddlCountries.DataSource = GetData("SELECT * FROM TBCourse  INNER JOIN TbCourseMajor ON  TBCourse.CId = TbCourseMajor.CId ");
            ddlCountries.DataTextField = "CName";
            ddlCountries.DataValueField = "CId";
            ddlCountries.DataBind();

            //Add Default Item in the DropDownList
            ddlCountries.Items.Insert(0, new ListItem("Please select"));

            DropDownList ddlCName = GridView1.FooterRow.FindControl("ddlCName") as DropDownList;
            ddlCName.DataSource = GetData("SELECT * FROM TBCourse  INNER JOIN TbCourseMajor ON  TBCourse.CId = TbCourseMajor.CId ");
            ddlCName.DataTextField = "CName";
            ddlCName.DataValueField = "CId";
            ddlCName.DataBind();

            //Add Default Item in the DropDownList
            ddlCName.Items.Insert(0, new ListItem("Please select"));

        }
    }

Answer 1

由于asp.net GridView上的<charset-params> <input-charset> <resource-path>/*</resource-path> <java-charset-name>UTF-8</java-charset-name> </input-charset> </charset-params>在Grid和页脚行中的每个数据绑定行之后触发可能没有绑定...所以OnRowDataBound很自然......所以你可以做以下事情。

在rowDataBound中找到GridView中的页脚

和更新数据库

如此完整的代码

的.aspx

System.NullReferenceException.

和.cs

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 
            ShowFooter="True" ondatabound="GridView1_DataBound">
    <Columns>
      <asp:BoundField HeaderText="EId" DataField="UserId" />
        <asp:TemplateField HeaderText = "CName">
            <ItemTemplate>
                <asp:Label ID="lblCountry" runat="server" Text='<%# Eval("UserId") %>' Visible = "True" />

            </ItemTemplate>
             <FooterTemplate>

              <asp:DropDownList ID="ddlCName"  CssClass="auto-style16" Width="80px" runat="server" >
                  <asp:ListItem Selected="True">1</asp:ListItem>
                  <asp:ListItem>2</asp:ListItem>
                 </asp:DropDownList>


        </FooterTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Answer 2

这是有效的：

 protected void GridView1_DataBound1(object sender, EventArgs e)
        {
            //GridViewRow row = GridView1.FooterRow;

            //var CName = ((DropDownList)row.Cells[1].FindControl("ddlCName")).SelectedValue;
            //var s = CName;

            DropDownList ddlCName = GridView1.FooterRow.FindControl("ddlCName") as DropDownList;
            ddlCName.DataSource = GetData("SELECT * FROM TBCourse  INNER JOIN TbCourseMajor ON  TBCourse.CId = TbCourseMajor.CId ");
            ddlCName.DataTextField = "CName";
            ddlCName.DataValueField = "CId";
            ddlCName.DataBind();

            //Add Default Item in the DropDownList
            ddlCName.Items.Insert(0, new ListItem("Please select"));
        }

对于网格视图中的下拉列表页脚（NullReferenceException）

2 个答案: