当Excel表里有多行時会报c#System.NullReferenceException:“未将对象引用设置到对象的实例。”，请问哪里出问题了

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.OleDb;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Oracle.ManagedDataAccess.Client;

namespace excel表导入oracle
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
OpenFileDialog openFileDialog1 = new OpenFileDialog();
openFileDialog1.Filter = "电子表格(*.xls)|*.xlsx";
openFileDialog1.ShowDialog();//打开对话框
this.textBox1.Text = openFileDialog1.FileName;//得到文件=路径+名称
}

private void button2_Click(object sender, EventArgs e)
{
try
{

DataSet ds = ImportExcel(this.textBox1.Text);//将excel的对象先放到ds 中
if (ds != null)
{
if (ds.Tables[0].Rows.Count > 0)//如果ds中是有值的话 执行下面的操作
{
if (ExportInfo(ds))
{
MessageBox.Show("导入数据库成功!");
}
else
{
MessageBox.Show("导入数据库失败!");
}
}

}
}
catch
{

MessageBox.Show("导入数据库失败 请检查导入文件是否填写正确!");
}


}

public static DataSet ImportExcel(string file)
{
FileInfo fileInfo = new FileInfo(file);
if (!fileInfo.Exists) return null; string strConn = "Provider=Microsoft.Ace.OleDb.12.0;" + "data source=" + file + ";Extended Properties='Excel 12.0; HDR=Yes; IMEX=1'";
OleDbConnection objConn = new OleDbConnection(strConn);
DataSet dsExcel = new DataSet();
try
{
objConn.Open();
string strSql = "select * from [Sheet1$]";
OleDbDataAdapter odbcExcelDataAdapter = new OleDbDataAdapter(strSql, objConn);
odbcExcelDataAdapter.Fill(dsExcel); return dsExcel;
}
catch (Exception ex)
{
throw ex;
}
}
/// <summary>
/// 这是将ds对象导入数据库的方法
/// 代云超
/// </summary>
/// <returns>执行是否成功 如: 成功=true 失败=false</returns>
public static bool ExportInfo(DataSet ds)
{
if (ds != null)
{
if (ds.Tables[0].Rows.Count > 0)//如果ds中是有值的话 执行下面的操作
{
return Do(ds);//执行成功
}
}
return false;//执行失败
}
public static bool Do(DataSet ds)
{
OracleConnection conNorthwind = new OracleConnection("Data Source=(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=127.0.0.1)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=orcl)));Persist Security Info=True;User ID=system;Password=orcl;");//链接字符串
OracleCommand commandNorthwind = new OracleCommand();
try
{

conNorthwind.Open();//打开数据库链接
OracleTransaction tranNorthwind = conNorthwind.BeginTransaction();//开始事务
Console.WriteLine("行数"+ds.Tables[0].Rows.Count);
for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
{
DataRow dr = ds.Tables[0].Rows[i];

OracleParameter[] parameters = null;//为了得到插入数据库的参数 定义参数对象 为空
string sql = GetSqlString(dr, out parameters);//执行sql -->用out关键字得到参数 赋到parameters对象上
//插入数据库中
PrepareCommand(commandNorthwind, conNorthwind, tranNorthwind, sql, parameters);
Console.WriteLine("liyaxuan测试仪"+ sql.ToString());
int a= commandNorthwind.ExecuteNonQuery();//执行操作
Console.WriteLine(a);
}
commandNorthwind.Transaction.Commit();//提交事务
conNorthwind.Close();//关闭数据库链接资源
return true;
}
catch//如果有异常 不一定要捕捉异常 但要rollback事务
{
if (commandNorthwind.Transaction != null && conNorthwind != null)
{
commandNorthwind.Transaction.Rollback();//rollback事务
conNorthwind.Close();//关闭数据库链接
}
return false;
}
}
/// <summary>
/// 每一行信息插入数据库中
/// </summary>
/// <param name="dr">要插入的这一行ds-datarow对象</param>
/// <returns>sql语句和用out关键字的参数数组对象</returns>
public static string GetSqlString(DataRow dr, out OracleParameter[] parameters)
{
StringBuilder sb = new StringBuilder();
sb.Append("INSERT INTO LIYAXUAN.TEXT(ID,NAME) VALUES(:ID,:NAME)");
parameters = new OracleParameter[] { new OracleParameter(":ID", Convert.ToString(dr[0])), new OracleParameter(":NAME", Convert.ToString(dr[1])) };
Console.WriteLine("ID的值"+ dr[0]);
Console.WriteLine("name的值" + dr[1]);
return sb.ToString();//将sqlreturn出去
}
private static void PrepareCommand(OracleCommand cmd, OracleConnection conn, OracleTransaction trans, string cmdText, OracleParameter[] cmdParms)
{
PrepareCommand(cmd, conn, trans, cmdText, CommandType.Text, cmdParms);
}
//参数设定 此方法被重载
private static void PrepareCommand(OracleCommand cmd, OracleConnection conn, OracleTransaction trans, string cmdText, CommandType cmdType, OracleParameter[] cmdParms)
{
if (conn.State != ConnectionState.Open)
{
conn.Open();
}
cmd.Connection = conn;
cmd.CommandText = cmdText;
if (trans != null)
{
cmd.Transaction = trans;
}
cmd.CommandType = cmdType; // CommandType.Text;//cmdType;
if (cmdParms != null)
{
foreach (OracleParameter parameter in cmdParms)
{
if (parameter != null)
{
if (parameter.Value == null)
{
parameter.Value = DBNull.Value;
}
cmd.Parameters.Add(parameter);
Console.WriteLine("parameter:" + parameter);
}
}
}
}
}
}