c# - 在 checkboxList 中的 SelectedIndexChanged ListItem 上重复

Question

每次在 SelectedIndexChanged 上，都会在 checkboxList 中创建一个新的 ListItem。我只需要显示从下拉列表中选择的 listItem。

 protected void ddlgrade_SelectedIndexChanged(object sender, EventArgs e)
            {
                string gradeid = ddlgrade.SelectedValue;
    
                if (Convert.ToInt32(gradeid) != -1 )
                {
                    SqlCommand cmd = new SqlCommand();
                    cmd.CommandType = CommandType.Text;
                    cmd.CommandText = "SELECT t.subject_name,t.subject_id from tblsubject t where NOT EXISTS(SELECT sg.subject_id from tblsubject_grade sg where t.subject_id = sg.subject_id and sg.grade_id = @g_Name)";
                    cmd.Connection = con;
                    cmd.Parameters.AddWithValue("@g_Name", gradeid);
                    SqlDataReader dr;
                    con.Open();
                    dr = cmd.ExecuteReader();
                    while (dr.Read())
                    {
                        ListItem item = new ListItem();
                        item.Text = dr["subject_name"].ToString();
                        item.Value = dr["subject_id"].ToString();
                        CheckBoxList1.Items.Add(item);
                    }
                }

示例 1 示例 2

标签： c#asp.net