C#中DBNull问题

/// <summary>
/// 插入数据
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void button2_Click(object sender, RoutedEventArgs e)
{
string name = txtName.Text;
string age = txtAge.Text;
string height = txtHeight.Text;
object objName;
if (name.Length <= 0)
{
objName = DBNull.Value;
}
else
{
objName = name;
}
object objAge;
if (age.Length <= 0)
{
objAge = DBNull.Value;
}
else
{
objAge = age;
}
object objHeight;
if (height.Length <= 0)
{
objHeight = DBNull.Value;
}
else
{
objHeight = height;
}
SqlHelper.ExecuteNonQuery(@"insert into T_Person(Name,Age,Height) values (@Name,@Age,@Height)",
new SqlParameter("@Name", objName),
new SqlParameter("@Age", objAge),
new SqlParameter("@Height", objHeight));
}
/// <summary>
/// 读出数据
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void button3_Click(object sender, RoutedEventArgs e)
{
DataSet ds = SqlHelper.ExecuteDataSet("select * from T_Person where id=2");

string name;
if (ds.Tables[0].Rows[0]["Name"] == DBNull.Value)
{
name = null;
}
else
{
name = ds.Tables[0].Rows[0]["Name"].ToString();
}
int? age;
if (ds.Tables[0].Rows[0]["Age"] == DBNull.Value)
{
age = null;
}
else
{
age = int.Parse(ds.Tables[0].Rows[0]["Age"].ToString());
}
txtName.Text = name;
txtAge.Text = age.ToString();
txtHeight.Text=ds.Tables[0].Rows[0]["Height"].ToString();
}