使用两个数据表时如何清除数据表值？

Question

通过查询后我有两个数据表，第二个数据表显示第一个数据表值。请找到我的代码

我的连接class是

 public class Connection
 {
  conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ApplicationServices"].ConnectionString);
  public SqlDataAdapter ad;
  public DataTable dt = new DataTable();
  public DataTable gettable(string cmdtxt)
    {
        if (conn.State == ConnectionState.Open)
        {
            conn.Close();
        }
        conn.Open();

        dt.Clear();

        ad = new SqlDataAdapter(cmdtxt, conn);
        ad.Fill(dt);
        return dt;
    }
  }

我的密码是

 String qry="";
 DataTable shiftdt = new DataTable();
 DataTable empdt = new DataTable();   
 qry = "select ShiftID from ShiftGroup  where ShiftName="@Shift";
 shiftdt = conn.gettable(qry);
 qry = "select EmpCode from EmployeeShift where GroupCode="@gcode";
 empdt = conn.gettable(qry);

首先，shiftdt 显示正确的输出 ShiftID，当继续时，empdt 将第一列显示为 ShiftID，将第二列显示为 EmpCode。实际上我不想在 empdt 中使用 ShiftID。当我继续时，Shiftdt 值再次更改为 EmpCode。我可以知道原因吗？

I tried `Dot net learner,when I change code as per him, I have a dropdown class it shows error like

`Error  8   'Sample.Connection' does not contain a definition for 'dt' and no extension method 'dt' accepting a first argument of type 'Sample.Connection' could be found (are you missing a using directive or an assembly reference?

。该课程是

 public class Dropdown
{

    Connection con = new Connection();
    public void dropdwnlist(string qry, DropDownList ddl)
    {
       con.gettable(qry);
       if (con.dt.Rows.Count > 0)
       {
           if (con.dt.Columns.Count == 2)
           {
               string str1 = con.dt.Columns[0].ColumnName.ToString();
               string str2 = con.dt.Columns[1].ColumnName.ToString();
               ddl.DataValueField = str1;
               ddl.DataTextField = str2;
               ddl.DataSource = con.dt;
               ddl.DataBind();
               con.dt.Columns.Remove(str1);
               con.dt.Columns.Remove(str2);

           }
           else
           {  
               string str = con.dt.Columns[0].ColumnName.ToString();
               ddl.DataValueField = str;
               ddl.DataTextField = str;
               ddl.DataSource = con.dt;
               ddl.DataBind();
               con.dt.Columns.Remove(str);
           }

       } 
           ddl.Items.Insert(0, ("--Select--"));
    }
}

Answer 1

您在 Class 中将 dt 作为全局变量，因此请将其设为函数的局部变量或在启动可获取函数时分配新的 DataTable。

您修改后的代码应该是

 public class Connection
{
 conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ApplicationServices"].ConnectionString);
public SqlDataAdapter ad;

public DataTable gettable(string cmdtxt)
{
    DataTable dt = new DataTable();
    if (conn.State == ConnectionState.Open)
    {
        conn.Close();
    }
    conn.Open();

    dt.Clear();

    ad = new SqlDataAdapter(cmdtxt, conn);
    ad.Fill(dt);
    return dt;
}
}

我已经根据您的需要修改了代码，请查看。

您不应使用连接 Class DataTable(dt) 变量来绑定下拉列表，而应为下拉列表声明本地 DataTable 变量 Class 并使用它来绑定下拉列表。

下拉菜单的修订代码 Class

public class Dropdown
{

Connection con = new Connection();
public void dropdwnlist(string qry, DropDownList ddl)
{
DataTable dt =con.gettable(qry);
   if (dt.Rows.Count > 0)
   {
       if (dt.Columns.Count == 2)
       {
           string str1 = dt.Columns[0].ColumnName.ToString();
           string str2 = dt.Columns[1].ColumnName.ToString();
           ddl.DataValueField = str1;
           ddl.DataTextField = str2;
           ddl.DataSource = dt;
           ddl.DataBind();
           dt.Columns.Remove(str1);
           dt.Columns.Remove(str2);

       }
       else
       {  
           string str = dt.Columns[0].ColumnName.ToString();
           ddl.DataValueField = str;
           ddl.DataTextField = str;
           ddl.DataSource = dt;
           ddl.DataBind();
           dt.Columns.Remove(str);
       }

   } 
       ddl.Items.Insert(0, ("--Select--"));
    }
 }

使用两个数据表时如何清除数据表值？

How to clear datatable values when using two datatables?

c#

datatable