我正在尝试将特定的 gridview 数据移动到 excel 文件中，但出现错误object reference not set to the instance of an object
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns = "false" Font-Names = "Arial"
Font-Size = "11pt" AlternatingRowStyle-BackColor = "#C2D69B"
HeaderStyle-BackColor = "green">
<Columns>
<asp:TemplateField>
<HeaderTemplate>
<asp:CheckBox ID="Chckcol0" runat="server" Checked="true"/>
<asp:Label ID="lbl_catid" runat="server" Text=" CategoryID"></asp:Label>
</HeaderTemplate>
<ItemTemplate>
<asp:Label ID="lbl_catid" runat="server" Text='<%# Eval("cat_id")%>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField>
<HeaderTemplate>
<asp:CheckBox ID="Chckcol1" runat="server" Checked="true"/>
<asp:Label ID="lbl_catname" runat="server" Text="category Name"></asp:Label>
</HeaderTemplate>
<ItemTemplate>
<asp:Label ID="lbl_categoryname" runat="server" Text='<%# Eval("categoryname")%>'> </asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField>
<HeaderTemplate>
<asp:CheckBox ID="Chckcol2" runat="server" Checked="true"/>
<asp:Label ID="description" runat="server" Text="description"></asp:Label>
</HeaderTemplate>
<ItemTemplate>
<asp:Label ID="lbl_description" runat="server" Text='<%# Eval("description")%>'> </asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
而我背后的代码：
public partial class _Default : System.Web.UI.Page
{
MySqlConnection con = new MySqlConnection("Data Source=localhost;Database=mylibrary_db;User ID=root;Password=MyLuck2010");
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
fillgrid();
}
}
protected void fillgrid()
{
MySqlDataAdapter da = new MySqlDataAdapter("select cat_id,categoryname,description from library_category", con);
DataSet ds = new DataSet();
da.Fill(ds);
GridView1.DataSource = ds;
GridView1.DataBind();
}
protected void getcheckedgridview()
{
CheckBox chkCol0 = (CheckBox)GridView1.HeaderRow.Cells[0].FindControl("chkCol0");
CheckBox chkCol1 = (CheckBox)GridView1.HeaderRow.Cells[0].FindControl("chkCol1");
CheckBox chkCol2 = (CheckBox)GridView1.HeaderRow.Cells[0].FindControl("chkCol2");
ArrayList arr;
if (ViewState["States"] == null)
{
arr = new ArrayList();
}
else
{
arr = (ArrayList)ViewState["States"];
}
arr.Add(chkCol0.Checked);
arr.Add(chkCol1.Checked);
arr.Add(chkCol2.Checked);
ViewState["States"] = arr;
}
protected void btnExportExcel_Click(object sender, EventArgs e)
{
Response.Clear();
Response.Buffer = true;
Response.AddHeader("content-disposition","attachment;filename=GridViewExport.xls");
Response.Charset = "";
Response.ContentType = "application/vnd.ms-excel";
StringWriter sw = new StringWriter();
HtmlTextWriter hw = new HtmlTextWriter(sw);
GridView1.AllowPaging = false;
GridView1.DataBind();
GridView1.HeaderRow.Style.Add("background-color", "#FFFFFF");
GridView1.HeaderRow.Cells[0].Style.Add("background-color", "green");
GridView1.HeaderRow.Cells[1].Style.Add("background-color", "green");
GridView1.HeaderRow.Cells[2].Style.Add("background-color", "green");
ArrayList arr = (ArrayList)ViewState["States"];
GridView1.HeaderRow.Cells[0].Visible = Convert.ToBoolean(arr[0]);
GridView1.HeaderRow.Cells[1].Visible = Convert.ToBoolean(arr[1]);
GridView1.HeaderRow.Cells[2].Visible = Convert.ToBoolean(arr[2]);
GridView1.HeaderRow.Cells[0].FindControl("chkCol0").Visible = false;
GridView1.HeaderRow.Cells[1].FindControl("chkCol1").Visible = false;
GridView1.HeaderRow.Cells[2].FindControl("chkCol2").Visible = false;
for (int i = 0; i < GridView1.Rows.Count; i++)
{
GridViewRow row = GridView1.Rows[i];
row.Cells[0].Visible = Convert.ToBoolean(arr[0]);
row.Cells[1].Visible = Convert.ToBoolean(arr[1]);
row.Cells[2].Visible = Convert.ToBoolean(arr[2]);
row.BackColor = System.Drawing.Color.White;
row.Attributes.Add("class", "textmode");
if (i % 2 != 0)
{
row.Cells[0].Style.Add("background-color", "#C2D69B");
row.Cells[1].Style.Add("background-color", "#C2D69B");
row.Cells[2].Style.Add("background-color", "#C2D69B");
}
}
GridView1.RenderControl(hw);
string style = @"<style> .textmode { mso-number-format:\@; } </style>";
Response.Write(style);
Response.Output.Write(sw.ToString());
Response.End();
}
}