datagridview中事务的问题，“事务不是与当前连接无关联，就是已完成”
小弟在form里就放了一个datagridview和一个button
想利用datagridview实现对表的直接修改，但是现在只能添加行不能修改，修改就提示“事务不是与当前连接无关联，就是已完成”
public partial class Form1 : Form
  {
  public Form1()
  {
  InitializeComponent();
  }
   
  SqlDataAdapter adapter;
  DataSet ds = new DataSet();
  private void Form1_Load(object sender, EventArgs e)
  {
  SqlConnection sqlconn = new SqlConnection("Server=.;DataBase=user;uid=sa;pwd=sa");
  try
  {
  //select语句中一定要包含主键字段，否则无法更新
  adapter = new SqlDataAdapter("select stuno'学号',stuname'姓名' from stuinf", sqlconn);//表里就两个字段，stuno和stuname
  adapter.Fill(ds, "student");
  dataGridView1.AutoGenerateColumns = true;
  dataGridView1.DataSource = ds.Tables["student"]; 
  sqlconn.Close();
  }
  catch (Exception ex)
  {
  MessageBox.Show(ex.ToString(), "异常错误!", MessageBoxButtons.OK, MessageBoxIcon.Error);

  }
  }

  private void btnUpdate_Click(object sender, EventArgs e)
  {
   
  try
  {
  SqlConnection conn = new SqlConnection("Server=.;DataBase=user;uid=sa;pwd=sa");
  SqlCommandBuilder sBuilder = new SqlCommandBuilder(adapter);
  adapter.UpdateCommand = sBuilder.GetUpdateCommand();
  conn.Open();
  SqlTransaction Trans = conn.BeginTransaction();  
  try
  {
  adapter.UpdateCommand.Transaction = Trans;
  adapter.Update(ds, "student"); 
  Trans.Commit();
  }
  catch (Exception ex)
  {
  Trans.Rollback();
  MessageBox.Show(this, ex.ToString(), "提示信息", MessageBoxButtons.OK, MessageBoxIcon.Information);
  return;
  }
  ds.Clear();
  adapter.Fill(ds, "student");
  dataGridView1.AutoGenerateColumns = true;
  dataGridView1.DataSource = ds.Tables["student"];
  MessageBox.Show(this, "确定", "提示信息", MessageBoxButtons.OK, MessageBoxIcon.Information);

  }
  catch (Exception ex)
  {
  MessageBox.Show(ex.ToString(), "异常错误!", MessageBoxButtons.OK, MessageBoxIcon.Error);
  }


  }
  }

请各位告诉指教

------解决方案--------------------
private void btnUpdate_Click(object sender, EventArgs e) 
{ 

try 
{ 
SqlConnection conn = new SqlConnection("Server=.;DataBase=user;uid=sa;pwd=sa"); 
//......
adapter.UpdateCommand.Transaction = Trans; 
adapter.Update(ds, "student"); 
Trans.Commit(); 
}