如何在點擊asp.net中的[show]按鈕時從數據庫中選擇下拉列表中的選項來填充其他下拉列表？

Question

大家好我一直在努力中，我有4個下拉列表是ddlpackage，ddlcategory，ddlsubcategory，ddlpackageprice分別命名爲顯示 以下按鈕是前端的圖像的項目：Image of Front end 這裏是形象數據庫中的表Image of tables from which i have retreived data to show in dropdownlist 現在我遇到的問題是，當從ddlpackage中選擇一個選項，然後單擊顯示我只是得到ddlcategory上的選項，然後再次點擊顯示按鈕即時獲取選項上ddlsubcategory，然後我有再次點擊顯示按鈕以獲得ddlpackage價格的選項。我想顯示所有選項，單擊顯示按鈕，並選擇下拉列表ddlpackage這裏是我的C＃代碼：

private String strConnection = @"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\PROJECT SEM6\Online Tours and Travels\App_Data\ToursandTravels.mdf;Integrated Security=True;User Instance=True"; 

protected void Page_Load(object sender, EventArgs e) 
{ 
    if (!IsPostBack) 
    { 
     BindPackageDropdown(); 
    } 
} 
protected void BindPackageDropdown() 
{ 
    //conenction path for database 
    SqlConnection con = new SqlConnection(strConnection); 
    con.Open(); 
    SqlCommand cmd = new SqlCommand("select * from package", con); 
    SqlDataAdapter da = new SqlDataAdapter(cmd); 
    DataSet ds = new DataSet(); 
    da.Fill(ds); 
    con.Close(); 
    ddlpackage.DataSource = ds; 
    ddlpackage.DataTextField = "packname"; 
    ddlpackage.DataValueField = "packid"; 
    ddlpackage.DataBind(); 
    ddlpackage.Items.Insert(0, new ListItem("--Select--", "0")); 
    ddlcategory.Items.Insert(0, new ListItem("--Select--", "0")); 
} 
protected void ddlpackage_SelectedIndexChanged(object sender, EventArgs e) 
{ 
    int packageid = Convert.ToInt32(ddlpackage.SelectedValue); 
    SqlConnection con = new SqlConnection(strConnection); 
    con.Open(); 
    SqlCommand cmd = new SqlCommand("select * from category where Cat_id=" + packageid, con); 
    SqlDataAdapter da = new SqlDataAdapter(cmd); 
    DataSet ds = new DataSet(); 
    da.Fill(ds); 
    con.Close(); 
    ddlcategory.DataSource = ds; 
    ddlcategory.DataTextField = "Cat_name"; 
    ddlcategory.DataValueField = "Cat_id"; 
    ddlcategory.DataBind(); 
    ddlcategory.Items.Insert(0, new ListItem("--Select--", "0")); 
} 


protected void ddlcategory_SelectedIndexChanged(object sender, EventArgs e) 
{ 
    int categoryid = Convert.ToInt32(ddlcategory.SelectedValue); 
    SqlConnection con = new SqlConnection(strConnection); 
    con.Open(); 
    SqlCommand cmd = new SqlCommand("select * from subcategory where catid=" + categoryid, con); 
    SqlDataAdapter da = new SqlDataAdapter(cmd); 
    DataSet ds = new DataSet(); 
    da.Fill(ds); 
    con.Close(); 
    ddlsubcategory.DataSource = ds; 
    ddlsubcategory.DataTextField = "subcatname"; 
    ddlsubcategory.DataValueField = "subcatid"; 
    ddlsubcategory.DataBind(); 
    ddlsubcategory.Items.Insert(0, new ListItem("--Select--", "0")); 
} 
protected void ddlsubcategory_SelectedIndexChanged(object sender, EventArgs e) 
{ 

    int subcategoryid = Convert.ToInt32(ddlsubcategory.SelectedValue); 
    SqlConnection con = new SqlConnection(strConnection); 
    con.Open(); 
    SqlCommand cmd = new SqlCommand("select * from package where packid=" + subcategoryid, con); 
    SqlDataAdapter da = new SqlDataAdapter(cmd); 
    DataSet ds = new DataSet(); 
    da.Fill(ds); 
    con.Close(); 
    ddlpackageprice.DataSource = ds; 
    ddlpackageprice.DataTextField = "packageprice"; 
    ddlpackageprice.DataValueField = "packageprice"; 
    ddlpackageprice.DataBind(); 
    ddlpackageprice.Items.Insert(0, new ListItem("--Select--", "0")); 
} 

請幫忙對不起我的英文...謝謝！

Answer 1

您無需再次單擊「顯示」按鈕。當第一次加載頁面時，您通過加載第一個下拉列表來執行正確的操作，這裏是您的代碼已經在執行此操作。 protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { BindPackageDropdown(); } }

現在你只需要確保每一個下拉列表中，只要您更改在下拉列表中選擇，相應的事件會被解僱例如：ddlsubcategory_SelectedIndexChanged等