"System.Exception: 未将对象引用设置到对象的实例。"是怎么回事?

Question

我看见一个人总结的gridview方法很好,就想直接用到自己的东西里,但是为什么会显示"System.Exception: 未将对象引用设置到对象的实例。"
异常详细信息: System.Exception: 未将对象引用设置到对象的实例。源错误: 
行 96:         catch (Exception e)
行 97:         {
行 98:             throw new Exception(e.Message);行 99:         }
行 100:        finally
 类common如下using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Collections;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.OleDb;/// <summary>
///Common 的摘要说明
/// </summary>
public class Common
{
    private static OleDbConnection conn = new OleDbConnection();
    private static OleDbCommand comm = new OleDbCommand();
public Common()
{
//
//TODO: 在此处添加构造函数逻辑
//
}
    /// <summary>
    /// 打开连接
    /// </summary>
    private static void openConnection()
    {
        if (conn.State == ConnectionState.Closed)
        {
            try
            {
                conn.ConnectionString = System.Web.Configuration.WebConfigurationManager.ConnectionStrings["connStr"].ConnectionString;
                comm.Connection = conn;
                conn.Open();
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }
        }
    }
    /// <summary>
    /// 关闭连接
    /// </summary>
    private static void closeConnection()
    {
        if (conn.State == ConnectionState.Open)
        {
            conn.Close();
        }
        conn.Dispose();
        comm.Dispose();
    }
    /// <summary>
    /// 执行一条sql语句
    /// </summary>
    /// <param name="sqlStr">sql语句</param>
    public static void ExecuteSql(string sqlStr)
    {
        try
        {
            openConnection();
            comm.CommandType = CommandType.Text;
            comm.CommandText = sqlStr;
            comm.ExecuteNonQuery();
        }
        catch (Exception e)
        {
            throw new Exception(e.Message);
        }
        finally
        {
            closeConnection();
        }
    }
    /// <summary>
    /// 返回一个数据集
    /// </summary>
    /// <param name="sqlStr">sql语句</param>
    /// <returns></returns>
    public static DataSet dataSet(string sqlStr)
    {
        OleDbDataAdapter da = new OleDbDataAdapter();
        DataSet ds = new DataSet();
        try
        {
            openConnection();
            comm.CommandType = CommandType.Text;
            comm.CommandText = sqlStr;
            da.SelectCommand = comm;
            da.Fill(ds);
        }
        catch (Exception e)
        {
            throw new Exception(e.Message);
        }
        finally
        {
            closeConnection();
        }
        return ds;
    }
    /// <summary>
    /// 返回一个数据视图
    /// </summary>
    /// <param name="sqlStr">sql语句</param>
    /// <returns></returns>
    public static DataView dataView(string sqlStr)
    {
        OleDbDataAdapter da = new OleDbDataAdapter();
        DataView dv = new DataView();
        DataSet ds = new DataSet();
        try
        {
            openConnection();
            comm.CommandType = CommandType.Text;
            comm.CommandText = sqlStr;
            da.SelectCommand = comm;
            da.Fill(ds);
            dv = ds.Tables[0].DefaultView;
        }
        catch (Exception e)
        {
            throw new Exception(e.Message);
        }
        finally
        {
            closeConnection();
        }
        return dv;
    }
}代码如下:
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.IO;
using System.Text;
/// <summary>
/// Author:匆匆  Blog:http://www.cnblogs.com/huangjianhuakarl/
/// 将Gridview中的数据导出Excel表格
/// </summary>
public partial class admin_Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            bind();
        }
    }
    /// <summary>
    /// 数据绑定
    /// </summary>
    public void bind()
    {
        string sqlStr = "select * from Employee";
        DataSet myds = Common.dataSet(sqlStr);
        GridView1.DataSource = myds;
        GridView1.DataKeyNames = new string[] { "ID" };
        GridView1.DataBind();
    }
    /// <summary>
    /// 在 GridView 控件中的某个行被绑定到一个数据记录时发生。此事件通常用于在某个行被绑定到数据时修改该行的内容。
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        foreach (TableCell tc in e.Row.Cells)
        {
            tc.Attributes["style"] = "border-color:Black";
        }
        if (e.Row.RowIndex != -1)
        {
            int id = GridView1.PageIndex * GridView1.PageSize + e.Row.RowIndex + 1;
            e.Row.Cells[0].Text = id.ToString();
        }
    }
    /// <summary>
    /// 导出Excel
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void Button1_Click(object sender, EventArgs e)
    {
        Export("application/ms-excel", "Employee information.xls");
    }
    /// <summary>
    /// 定义导出Excel的函数
    /// </summary>
    /// <param name="FileType"></param>
    /// <param name="FileName"></param>
    private void Export(string FileType, string FileName)
    {
        Response.Charset = "GB2312";
        Response.ContentEncoding = System.Text.Encoding.UTF8;
        Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(FileName, Encoding.UTF8).ToString());
        Response.ContentType = FileType;
        this.EnableViewState = false;
        StringWriter tw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(tw);
        GridView1.RenderControl(hw);
        Response.Write(tw.ToString());
        Response.End();
    }
    /// <summary>
    /// 此方法必重写，否则会出错
    /// </summary>
    /// <param name="control"></param>
    public override void VerifyRenderingInServerForm(Control control)
    {
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        //Export("application/ms-excel", "Employee.doc");
        Export("application/ms-word", "员工信息.doc");//都可以
    }
}

Answer 1

在程序中标出来时那块啊出错了啊，这样看着恼火的很……

Answer 2

是你自己把人家的异常捕获了，又抛得异常呀

Answer 3

看到这个错误就知道有值为空，应该贴关键代码就可以了，代码太长看不下去

Answer 4

我也遇到了同样的问题！解决了送分！兄弟们帮忙看看！