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動態產生DropDownList

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Default.aspx

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>無標題頁</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>  
        <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
        <br />
        <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" /></div>
    </form>
</body>
</html>

==============================================================================
Default.aspx.cs

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

using Model;
using BLL;

public partial class _Default : System.Web.UI.Page
{
    private CategoryBLL _categoryBLL = new CategoryBLL();
    private Category _category = new Category();

    private void Page_Init(object sender, System.EventArgs e)
    {
        BindDrpClass();
    }
    protected void Page_Load(object sender, EventArgs e)
    {
        string str = "8/14/19/25"; //資料庫讀取
        string[] arr = str.Split('/');
        if (arr.Length == PlaceHolder1.Controls.Count) //防止新增類別時讀取出錯
        {
            for (int i = 0; i < PlaceHolder1.Controls.Count; i++)
            {
                if (PlaceHolder1.Controls[i] is DropDownList)
                {
                    ((DropDownList)PlaceHolder1.Controls[i]).SelectedValue = arr[i];
                }
            }
        }
    }
  
    private void BindDrpClass()
    {
        DataTable dt = _categoryBLL.GetCategory();
        DataRow[] drs = dt.Select("pid=0");

        foreach (DataRow dr in drs)
        {
            string id = dr["id"].ToString();
            string name = dr["name"].ToString();

            DropDownList ddl = new DropDownList();
            ddl.Items.Clear();
            ddl.ID = "ddl" + id;
            ddl.Items.Add(new ListItem("－" + name + "－", id));
            PlaceHolder1.Controls.Add(ddl);

            int sonparentid = int.Parse(id);
            BindDrpNode(sonparentid, dt, ddl);
        }

    }

    private void BindDrpNode(int parentid, DataTable dt, DropDownList ddl)
    {
        DataRow[] drs = dt.Select("pid= " + parentid);
        foreach (DataRow dr in drs)
        {
            string id = dr["id"].ToString();
            string name = dr["name"].ToString();

            ddl.Items.Add(new ListItem(name, id));         
            PlaceHolder1.Controls.Add(ddl);
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string category = "";
        string category2 = "";
        foreach (Control childControl in PlaceHolder1.Controls)
        {
            if (childControl is DropDownList)
            {
                category += "/" + ((DropDownList)childControl).SelectedItem.Text;
                category2 += "/" + ((DropDownList)childControl).SelectedValue;  
            }
        }
        if (category.Length > 0)
            category = category.Remove(0, 1);
        Response.Write(category);

        Response.Write("<br />");

        if (category2.Length > 0)
            category2 = category2.Remove(0, 1);
        Response.Write(category2);
    }
}

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