级联DropDownList在ASP.Net c#中的应用

Question

我需要在cascading DropDownList in ASP.Net c#中创建一个DropDownList，它依赖于GridView.中的Footer Template中的数据的第一个DropDownList

当从第一个First_DDL_SelectedIndexChanged**.**中选择一个值时，我需要使用查询sql3的值填充第二个DropDownList

在调试中，在第一个DropDownList中选择的输出值和查询sql3是正确的。

我尝试过使用此解决方案，但没有成功，因为错误是：

Compiler Error Message: CS0103: 
The name 'dtSubCategories' does not exist in the current context

在这一行代码背后：

Line 360:
Second_DDL.DataSource = dtSubCategories();

如果你能帮我解决这个问题，我将不胜感激。

这是我的代码：

protected void First_DDL_SelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList First_DDL = (DropDownList)sender;
    GridViewRow row = (GridViewRow)First_DDL.NamingContainer;

    Response.Write(First_DDL.SelectedItem.ToString().Substring(0, 3) + "<br /><br />");

    sql3 = " SELECT FROM `tbl_m` WHERE fiedl1 = ?; ";

    Response.Write(sql3);

    DataTable dtSubCategories = new DataTable();

    using (OdbcConnection myConnectionString =
       new OdbcConnection(ConfigurationManager.ConnectionStrings["ConnMySQL"].ConnectionString))
    {
        myConnectionString.Open();
        using (OdbcCommand cmd = new OdbcCommand(sql3, myConnectionString))
        {
            OdbcDataAdapter adapter = new OdbcDataAdapter(cmd);
            cmd.Parameters.AddWithValue("param1", First_DDL.SelectedItem.ToString().Substring(0, 3));
            adapter.Fill(dtSubCategories);
        }
    }
}


protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.Footer)
    {
        DropDownList Second_DDL = (DropDownList)e.Row.FindControl("Second_DDL");
        Second_DDL.DataTextField = "text";
        Second_DDL.DataValueField = "text";
        Second_DDL.DataSource = dtSubCategories();
        Second_DDL.DataBind();

    }
}

编辑#1

DataTable dtSubCategories = new DataTable();


protected void First_DDL_SelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList First_DDL = (DropDownList)sender;
    GridViewRow row = (GridViewRow)First_DDL.NamingContainer;

    Response.Write(First_DDL.SelectedItem.ToString().Substring(0, 3) + "<br /><br />");

    sql3 = " SELECT FROM `tbl_m` WHERE fiedl1 = ?; ";

    Response.Write(sql3);

    DataTable dtSubCategories = new DataTable();

    using (OdbcConnection myConnectionString =
       new OdbcConnection(ConfigurationManager.ConnectionStrings["ConnMySQL"].ConnectionString))
    {
        myConnectionString.Open();
        using (OdbcCommand cmd = new OdbcCommand(sql3, myConnectionString))
        {
            OdbcDataAdapter adapter = new OdbcDataAdapter(cmd);
            cmd.Parameters.AddWithValue("param1", First_DDL.SelectedItem.ToString().Substring(0, 3));
            adapter.Fill(dtSubCategories);
        }
    }
}


    protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.Footer)
        {
            DropDownList Second_DDL = (DropDownList)e.Row.FindControl("Second_DDL");
            Second_DDL.DataTextField = "text";
            Second_DDL.DataValueField = "text";
            Second_DDL.DataSource = dtSubCategories();
            Second_DDL.DataBind();

        }
    }

编辑#2

using System;
using System.Configuration;
using System.Data;
using System.Data.Odbc;
using System.Globalization;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Level_Default2 : System.Web.UI.Page
{
    OdbcConnection cn =
       new OdbcConnection(ConfigurationManager.ConnectionStrings["cn"].ConnectionString);

    DataSet dset;
    DataTable dt = new DataTable();
    DataTable dtCategories = new DataTable();
    DataTable dtSubCategories = new DataTable();
    OdbcDataAdapter dadapter;

    private DataTable RetrieveSubCategories(string TRZ)
    {
        string sql3 = " SELECT ... where TRZ = ?; ";

        using (OdbcConnection cn =
            new OdbcConnection(ConfigurationManager.ConnectionStrings["cn"].ConnectionString))
        {
            cn.Open();
            using (OdbcCommand cmd = new OdbcCommand(sql3, cn))
            {
                dadapter = new OdbcDataAdapter(cmd);
                dadapter.SelectCommand.Parameters.AddWithValue(?, TRZ.SelectedItem.ToString().Substring(0, 3));
                dadapter.Fill(dtSubCategories);
            }
        }
        return dtSubCategories;
    }

    private DataTable RetrieveCategories()
    {
        string sql2 = " SELECT ... ; ";

        using (OdbcConnection cn =
           new OdbcConnection(ConfigurationManager.ConnectionStrings["cn"].ConnectionString))
        {
            cn.Open();
            using (OdbcCommand cmd = new OdbcCommand(sql2, cn))
            {
                dadapter = new OdbcDataAdapter(cmd);
                dadapter.Fill(dtCategories);
            }
        }
        return dtCategories;
    }

    protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.Footer)
        {
            DropDownList First_DDL = (DropDownList)e.Row.FindControl("First_DDL");
            First_DDL.DataTextField = "First_DDL";
            First_DDL.DataValueField = "First_DDL";
            First_DDL.DataSource = RetrieveCategories();
            First_DDL.DataBind();

            DropDownList Second_DDL = (DropDownList)e.Row.FindControl("Second_DDL");
            Second_DDL.DataTextField = "Second_DDL";
            Second_DDL.DataValueField = "Second_DDL";
            Second_DDL.DataSource = dtSubCategories;
            Second_DDL.DataBind();
        }
    }

    protected void First_DDL_SelectedIndexChanged(object sender, EventArgs e)
    {
        DropDownList TRZ = (DropDownList)sender;
        GridViewRow row = (GridViewRow)TRZ.NamingContainer;
        RetrieveSubCategories(TRZ.SelectedItem.ToString().Substring(0, 3));

        Response.Write(TRZ.SelectedItem.ToString().Substring(0, 3));
    }

    public DataTable GridViewBind()
    {
        using (OdbcConnection cn =
            new OdbcConnection(ConfigurationManager.ConnectionStrings["cn"].ConnectionString))
        {
            string sql1 = " SELECT ... ; ";

            using (OdbcDataAdapter command =
                new OdbcDataAdapter(sql1, cn))
            {
                cn.Open();
                dset = new DataSet();
                dset.Clear();
                command.Fill(dset);
                DataTable dt = dset.Tables[0];
                GridView1.DataSource = dt;
                GridView1.DataBind();
                return dt;
            }
        }
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            GridViewBind();
        }
    }
}

Answer 1

全局声明数据表。外部First_DDL_SelectedIndexChanged() function.Like

DataTable dtSubCategories = new DataTable();
protected void First_DDL_SelectedIndexChanged(object sender, EventArgs e)
{..}

您的问题是datatable是本地的，只有第一个下拉列表。

Answer 2

在扩展Yogi的答案和Rex的注释之后，当dtSubCategories是一个变量时，您也会像调用方法一样调用它。要么删除括号，要么创建方法/属性来检索数据表。

//using the global variable
Second_DDL.DataSource = dtSubCategories;

//using a property
Second_DDL.DataSource = DTSubCategories;
public DataTable DTSubCategories
{
    get { return dtSubCategories; }
    set { dtSubCategories = value; }
}

//using a method
Second_DDL.DataSource = GetSubCategories();
private DataTable GetSubCategories()
{
    return dtSubCategories;
}