C# ASP.net通过从表中预加载数据来加速dropdownlist加载

我有一个网格视图，它使用dropdownlist选择员工ID，但显示姓名

 <EditItemTemplate>
 <asp:DropDownList ID="DropDownList5" runat="server" AppendDataBoundItems="True" DataSourceID="SqlDataSourceEmployees" DataTextField="name" DataValueField="empID" SelectedValue='<%# Bind("employee") %>'>
                                <asp:ListItem></asp:ListItem>
                            </asp:DropDownList>
  </EditItemTemplate>

但是改变列表的绑定

<EditItemTemplate>
                            <asp:DropDownList ID="DropDownList5" runat="server" AppendDataBoundItems="True" DataSourceID="EmployeesTable" DataTextField="name" DataValueField="empID" SelectedValue='<%# Bind("employee") %>'>
                                <asp:ListItem></asp:ListItem>
                            </asp:DropDownList>

}

这并没有加快速度，我确信DDL仍然从SQL源获取数据（当我试图删除它时，我有一个错误，指出SelevtedValue无效）

所以我试着在编辑事件期间提前一步分配它

 protected void GridView5_RowEditing(object sender, GridViewEditEventArgs e)
{
    ((DropDownList)GridView5.FindControl("DropDownList5")).DataSource = EmployeesTable;
    ((DropDownList)GridView5.FindControl("DropDownList5")).DataBind();


}

但是它没有找到dropdownlist5

---

编辑：我放弃了。阅读之后，我简单地将SQLDataSource类型更改为DataReader，这确实提高了性能。或者这可能是对我疲惫的大脑的安慰剂效应。

你不能按你现在的方式来做，因为你的employeesTable变量在页面一送达就被销毁了。然后，每次回发都会获得一个新实例。如果列表不是唯一的，则将其存储到缓存对象中。然后还可以为其设置超时

如果它基于页面的数据，则可以将其存储在会话中，这样可以跨页面传输数据，但如果跨用户在会话中存储大量对象，则会降低性能

如果它不是太大，您可以将其存储在ViewState中。然后将其序列化到客户端。缺点是，数据可能会膨胀发送到客户端的HTML

在您的情况下，由于datatable似乎依赖于文本字段，因此最好使用viewstate。但是，在您的例子中，由于您需要知道文本值何时也发生了更改，以便可以否定数据，因此增加了复杂性

下面是ViewState的粗略示例，但您也可以针对会话和缓存进行调整

private string SelectedDepartmentText
{
    get
    {
        if(ViewState["SelectedDepartmentText"] != null)
            return ViewState["SelectedDepartmentText"].ToString();
        else
            return string.Empty;
    }
    set{ViewState["SelectedDepartmentText"] = value;}
}

public DataSet.employeesDataTable EmployeesTable
{
     get
    {
           if(!SelectedDepartmentText.Equals(lblDepartment.Text))
           {
               // if the SelectedDepartmentText isn't the same as the lblDepartment.Text, go fetch it
               DataSetTableAdapters.employeesTableAdapter TA = new DataSetTableAdapters.employeesTableAdapter();
               ViewState["EmployeesTable"] =TA.GetDataByDepartment(lblDepartment.Text);
               // save the lblDepartment.Text value to the viewstate for next time.
               SelectedDepartmentText = lblDepartment.Text;
               return ViewState["EmployeesTable"];
           }
           else
           {
               // let's see if we have something already and return it
               if(ViewState["EmployeesTable"] != null)
                   return (DataSet.employeesDataTable)ViewState["EmployeesTable"];
               else
                {

                // if we don't, let's get it, this also handles an empty string for the                     
                // lblDepartment.Text
            DataSetTableAdapters.employeesTableAdapter TA = new DataSetTableAdapters.employeesTableAdapter();
                        // store it in the viewstate
            ViewState["EmployeesTable"] =TA.GetDataByDepartment(lblDepartment.Text);
                        // and return whatever we got back
            return (DataSet.employeesDataTable)ViewState["EmployeesTable"];
                }
           }
           return null;
    }
    set{ ViewState["EmployeesTable"] = value;}
}

---

试着把你的数据表放到一个会话中，然后你可以让你的dropdownlist从会话中获取数据。我该怎么做呢？好吧，但我该如何将dropdownlist绑定到EmployeesTable上呢使用DataSourceId是错误的。用于表示数据源控件（如SqlDataSource）的ID。在Codebehind do中：DropDownList5.DataSource=EmployeesTable；DropDownList5.DataBind（）；它可能正在工作，但我无法将dropdownlist绑定到Employees表。。。（问题更新）

 protected void GridView5_RowEditing(object sender, GridViewEditEventArgs e)
{
    ((DropDownList)GridView5.FindControl("DropDownList5")).DataSource = EmployeesTable;
    ((DropDownList)GridView5.FindControl("DropDownList5")).DataBind();


}

private string SelectedDepartmentText
{
    get
    {
        if(ViewState["SelectedDepartmentText"] != null)
            return ViewState["SelectedDepartmentText"].ToString();
        else
            return string.Empty;
    }
    set{ViewState["SelectedDepartmentText"] = value;}
}

public DataSet.employeesDataTable EmployeesTable
{
     get
    {
           if(!SelectedDepartmentText.Equals(lblDepartment.Text))
           {
               // if the SelectedDepartmentText isn't the same as the lblDepartment.Text, go fetch it
               DataSetTableAdapters.employeesTableAdapter TA = new DataSetTableAdapters.employeesTableAdapter();
               ViewState["EmployeesTable"] =TA.GetDataByDepartment(lblDepartment.Text);
               // save the lblDepartment.Text value to the viewstate for next time.
               SelectedDepartmentText = lblDepartment.Text;
               return ViewState["EmployeesTable"];
           }
           else
           {
               // let's see if we have something already and return it
               if(ViewState["EmployeesTable"] != null)
                   return (DataSet.employeesDataTable)ViewState["EmployeesTable"];
               else
                {

                // if we don't, let's get it, this also handles an empty string for the                     
                // lblDepartment.Text
            DataSetTableAdapters.employeesTableAdapter TA = new DataSetTableAdapters.employeesTableAdapter();
                        // store it in the viewstate
            ViewState["EmployeesTable"] =TA.GetDataByDepartment(lblDepartment.Text);
                        // and return whatever we got back
            return (DataSet.employeesDataTable)ViewState["EmployeesTable"];
                }
           }
           return null;
    }
    set{ ViewState["EmployeesTable"] = value;}
}