谁能帮个忙啊。我的代码总是提示 “System.NullReferenceException: 未将对象引用设置到对象的实例”
Loken 2008-04-27 05:49:55 代码片段如下:
namespace OnlineExam2.DataAccessLayer
{
....
// 数据库接口类
public class DataBase
{
// 函数:
public DataSet GetDataSet(string ProcName, SqlParameter[] Params)
{
//Open();
SqlCommand Cmd = CreateCommand(ProcName, Params);
SqlDataAdapter adapter = new SqlDataAdapter(Cmd);
DataSet dataset = new DataSet();
adapter.Fill(dataset);
Close();
return dataset;
}
}
}
namespace OnlineExam2.BusinessLogicLayer
{
//用户类
public class Paper
{
public DataSet QueryPaper()
{
DataBase DB = new DataBase();
SqlParameter[] Params = new SqlParameter[1];
Params[0] = DB.MakeInParam("@PaperState", SqlDbType.Bit,1, "true"); //题目编号
return DB.GetDataSet("Proc_PaperUseList",Params);
}
}
}
调用:
Paper paper = new Paper(); //创建Paper对象
DataSet ds = paper.QueryPaper(); //查询所有可用试卷
try
{
if (ds != null && ds.Tables[0].Rows.Count >= 1)
{
ddlPaper1.DataSource = ds.Tables[0].DefaultView; //指名考试科目列表框数据源
ddlPaper1.DataTextField = "PaperName"; //DataTextField显示Name字段值
ddlPaper1.DataValueField = "PaperID"; //DataValueField显示ID字段值
ddlPaper1.DataBind(); //绑定数据
}
else
{
ddlPaper1.Enabled = false;
imgBtnLogin1.Enabled = false;
lblMessage1.Text = "没有试卷!";
}
}
catch (NullReferenceException e)
{
Response.Write(e.Message + ds.Tables[0].Rows.Count.ToString());
}
总是显示
System.NullReferenceException: 未将对象引用设置到对象的实例
谁有时间帮我可以留言,我将所有代码发过去看看。