DataReader怎样判断是否为空啊？

[greenhill]

我的程序因为DataReader读出的数据为空而出错，因为我的数据库里面没有数据，我想加个判断语句，判断datareader是否为空数据，请问怎样判断？？

[greenhill1]

我找到问题的根源了！是我的判断变量设置不对！和这段代码没有关系！感谢大家的帮助！

[greenhill1]

我找到问题的根源了！是我的判断变量设置不对！和这段代码没有关系！感谢大家的帮助！

[jjcccc]

OleDataReader reader;

while (reader.Read())
{
//...
}

[dding_ch]

DataReader dr = cmd.ExecuteReader();
if(dr.read()) //check whether the DataReader has got some values
{
...
}
dr.close();

[greenhill]

这些我知道啊！就这样它才出错啊，因为读不到数据！我想问怎样判断是否读到了数据？

[brightheroes]

show your code

[greenhill]

SqlCommand thisCommand=thisConnection.CreateCommand();
thisCommand.CommandText="SELECT * FROM 班级";
SqlDataReader thisReader=thisCommand.ExecuteReader();
while(thisReader.Read())
{
if(thisReader["年级"].ToString().Trim()==comboBox1.Text.Trim() && thisReader["班级名称"].ToString().Trim()==textBox1.Text.Trim())
{
MessageBox.Show("该班已存在！");
i=0;
thisReader.Close();
thisConnection.Close();
break;
}
else
{
i=1;
}
}

thisReader.Close();

if(i==1)
{
SqlDataAdapter thisAdapter=new SqlDataAdapter("SELECT * FROM 班级",thisConnection);
SqlCommandBuilder thisBuilder=new SqlCommandBuilder(thisAdapter);

DataSet thisDataSet=new DataSet();

thisAdapter.Fill(thisDataSet,"班级");

DataRow thisRow=thisDataSet.Tables["班级"].NewRow();
thisRow["年级"]=comboBox1.Text.Trim();
thisRow["班级名称"]=textBox1.Text.Trim();
thisRow["人数"]="0";
thisRow["班主任"]=textBox2.Text.Trim();
thisRow["班主任手机"]=textBox3.Text.Trim();

thisDataSet.Tables["班级"].Rows.Add(thisRow);

thisAdapter.Update(thisDataSet,"班级");

thisConnection.Close();

MessageBox.Show("修改成功！");

this.Close();

[maregister]

用IsNull方法。可以判断某个字段内容是否为空值

[dding_ch]

SqlCommand thisCommand=thisConnection.CreateCommand();
thisCommand.CommandText="SELECT * FROM 班级";
//把数据访问放到try ... catch ... 里，看看是否有异常抛出
try
{
SqlDataReader thisReader=thisCommand.ExecuteReader();
while(thisReader.Read())
{
if(thisReader["年级"].ToString().Trim()==comboBox1.Text.Trim() && thisReader["班级名称"].ToString().Trim()==textBox1.Text.Trim())
{
MessageBox.Show("该班已存在！");
i=0;
thisReader.Close();
thisConnection.Close();
break;
}
else
{
i=1;
}
}

thisReader.Close();

if(i==1)
{
SqlDataAdapter thisAdapter=new SqlDataAdapter("SELECT * FROM 班级",thisConnection);
SqlCommandBuilder thisBuilder=new SqlCommandBuilder(thisAdapter);

DataSet thisDataSet=new DataSet();

thisAdapter.Fill(thisDataSet,"班级");

DataRow thisRow=thisDataSet.Tables["班级"].NewRow();
thisRow["年级"]=comboBox1.Text.Trim();
thisRow["班级名称"]=textBox1.Text.Trim();
thisRow["人数"]="0";
thisRow["班主任"]=textBox2.Text.Trim();
thisRow["班主任手机"]=textBox3.Text.Trim();

thisDataSet.Tables["班级"].Rows.Add(thisRow);

thisAdapter.Update(thisDataSet,"班级");

thisConnection.Close();

MessageBox.Show("修改成功！");

this.Close();
}
catch(Exception e)
{
MessageBox.Show(e.Message);
}