SqlDataAdapter.Update 或 SqlCommandBuilder 不起作用

我有一个带有数据网格的表单，该表单由sqlserver数据库中的数据填充。 数据网格填充良好，但我无法将用户所做的更改回发到 sql 数据库中的表中。 我的表单代码如下：

public partial class frmTimesheet : Form
{
    private DataTable tableTS = new DataTable();
    private SqlDataAdapter adapter = new SqlDataAdapter();
    private int currentTSID = 0;
    public frmTimesheet()
    {
        InitializeComponent();
    }
    private void frmTimesheet_Load(object sender, EventArgs e)
    {
        string strUser = cUser.currentUser;            
        cMyDate cD = new cMyDate(DateTime.Now.ToString());
        DateTime date = cD.GetDate();
        txtDate.Text = date.ToString();
        cboTSUser.DataSource = cUser.GetListOfUsers("active");
        cboTSUser.DisplayMember = "UserID";
        cboTSUser.Text = strUser;
        CheckForTimeSheet();
        PopulateTimeSheet();
    }
    private void CheckForTimeSheet()
    {
        string strUser = cboTSUser.Text;
        cMyDate cD = new cMyDate(txtDate.Text);
        DateTime date = cD.GetDate();
        int newTSID = cTimesheet.TimeSheetExists(strUser, date);
        if (newTSID != this.currentTSID)
        {
            tableTS.Clear();
            if (newTSID == 0)
            {
                MessageBox.Show("Create TimeSheet");
            }
            else
            {
                this.currentTSID = newTSID;
            }
        }
    }
    private void PopulateTimeSheet()
    {
        try
        {
            string sqlText = "SELECT EntryID, CaseNo, ChargeCode, StartTime, FinishTime, Units " +
                             "FROM tblTimesheetEntries " +
                             "WHERE TSID = " + this.currentTSID + ";";
            SqlConnection linkToDB = new SqlConnection(cConnectionString.BuildConnectionString());
            SqlCommand sqlCom = new SqlCommand(sqlText, linkToDB);
            SqlDataAdapter adapter = new SqlDataAdapter(sqlCom);
            adapter.SelectCommand = sqlCom;
            SqlCommandBuilder builder = new SqlCommandBuilder(adapter);
            adapter.Fill(tableTS);
            dataTimesheet.DataSource = tableTS;                
        }
        catch (Exception eX)
        {
            string eM = "Error Populating Timesheet";
            cError err = new cError(eX, eM);
            MessageBox.Show(eM + Environment.NewLine + eX.Message);
        }         
    }
    private void txtDate_Leave(object sender, EventArgs e)
    {
        CheckForTimeSheet();
        PopulateTimeSheet();            
    }
    private void cboTSUser_DropDownClosed(object sender, EventArgs e)
    {
        CheckForTimeSheet(); 
        PopulateTimeSheet();
    }
    private void dataTimesheet_CellValueChanged(object sender, DataGridViewCellEventArgs e)
    {
        try
        {   
            adapter.Update(tableTS);
        }
        catch (Exception eX)
        {
            string eM = "Error on frmTimesheet, dataTimesheet_CellValueChanged";
            cError err = new cError(eX, eM);
            MessageBox.Show(eM + Environment.NewLine + eX.Message);
        }
    }
}

没有例外发生，当我逐步解决问题时，问题似乎与 SqlCommandBuilder 有关，它不会根据我的 gien SELECT 命令构建插入/更新/删除命令。

谁能看出我做错了什么？

我错过了什么？