动态创建控件

Question

I am doing a project for class but can't figure out this small pease that has being keeping me up nights. I am creating a page dynamically and it makes a panel for each entry in a database. Now the problem is i use one button for all the buttons on each panel. I need to be able to know what button was pressed so i can send the CarID in a session to another Page.

namespace SportBucks
{
public partial class Auction : System.Web.UI.Page
{
    string GCarID = "";
    protected void Page_Load(object sender, EventArgs e)
    {
        bool bWinnerID = false;
        bool bWiningBet = false;

        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        if ((string)Session["LoggedIn"] == null)
        {
            Response.Redirect("Default.aspx");
        }
        else
        {
            Service s = new Service();
            int Total = s.CarsCount();
            for (int loop = Total; loop > 0; loop--)
            {
                Panel Panel1 = new Panel();
                Panel1.ID = "pnl" + loop.ToString();
                Panel1.Style["position"] = "absolute";
                Panel1.Style["left"] = "155px";
                Panel1.Style["top"] = "250px";
                Panel1.Style["Height"] = "200px";
                Panel1.Style["Width"] = "1000px";
                Panel1.BackColor = System.Drawing.Color.Black;

                if (loop >= 2)
                {
                    int Top = (250 * (loop - 1));
                    Panel1.Style["top"] = (250 + Top + 20).ToString() + "px";
                }
                form1.Controls.Add(Panel1);
                string Details = s.LoadCars(loop);
                if (Details != null)
                {
                    string CarID = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(CarID + "|", "");
                    string Man = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(Man + "|", "");
                    string Class = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(Class + "|", "");
                    string Type = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(Type + "|", "");
                    string Description = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(Description + "|", "");
                    string Reserve = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(Reserve + "|", "");
                    string Starting = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(Starting + "|", "");
                    string Begun = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(Begun + "|", "");
                    Begun = Begun.Substring(0, Begun.IndexOf(" "));
                    string End = Details.Substring(0, Details.IndexOf("|"));
                    Details = Details.Replace(End + "|", "");
                    End = End.Substring(0, End.IndexOf(" "));
                    string WinnerID = "";
                    string WinningBet = "";
                    if (Details.Substring(0, 1) == "|")
                    {
                        bWinnerID = false;
                        Details = Details.Substring(1);
                    }
                    else
                    {
                        WinnerID = Details.Substring(0, Details.IndexOf("|"));
                        Details = Details.Replace(WinnerID + "|", "");
                        bWinnerID = true;
                    }

                    if (Details.Substring(0, 1) == "|")
                    {
                        Details = Details.Substring(1);
                        bWiningBet = false;
                    }
                    else
                    {
                        WinningBet = Details.Substring(0, Details.IndexOf("|"));
                        Details = Details.Replace(WinningBet + "|", "");
                        bWiningBet = true;
                    }

                    string PicUrl = Details.Substring(0, Details.IndexOf("|"));
                    int Counter = PicUrl.Split(';').Length - 1;
                    if (Counter >= 1)
                    {
                        Image image1 = new Image();
                        image1.ID = "img" + CarID;
                        image1.ImageAlign = ImageAlign.AbsMiddle;
                        image1.Visible = true;
                        string Pic1 = PicUrl.Substring(0, PicUrl.IndexOf(";"));
                        image1.ImageUrl = Pic1;
                        image1.Style["Left"] = "10px";
                        image1.Style["position"] = "absolute";
                        image1.Style["top"] = "10px";
                        image1.Height = 180;
                        image1.Width = 230;
                        Panel1.Controls.Add(image1);

                    }
                    Label label1 = new Label();
                    label1.ID = "lblDescription" + CarID;
                    label1.Text = Description;
                    label1.ForeColor = System.Drawing.Color.Lime;
                    label1.BorderStyle = BorderStyle.Groove;
                    label1.BorderColor = System.Drawing.Color.Violet;
                    label1.Style["Left"] = "500px";
                    label1.Style["position"] = "absolute";
                    label1.Style["top"] = "30px";
                    Panel1.Controls.Add(label1);

                    Label label2 = new Label();
                    label2.ID = "lblBegun" + CarID;
                    label2.Text = "Auction Start: " + Begun;
                    label2.ForeColor = System.Drawing.Color.Lime;
                    label2.Style["Left"] = "270px";
                    label2.Style["position"] = "absolute";
                    label2.Style["top"] = "30px";
                    Panel1.Controls.Add(label2);

                    Label label3 = new Label();
                    label3.ID = "lblEnd" + CarID;
                    label3.Text = "Auction End: " + End;
                    label3.ForeColor = System.Drawing.Color.Lime;
                    label3.Style["Left"] = "270px";
                    label3.Style["position"] = "absolute";
                    label3.Style["top"] = "50px";
                    Panel1.Controls.Add(label3);

                    Label label4 = new Label();
                    label4.ID = "lblReserve" + CarID;
                    label4.Text = "Reserve: " + Reserve;
                    label4.ForeColor = System.Drawing.Color.Lime;
                    label4.Style["Left"] = "270px";
                    label4.Style["position"] = "absolute";
                    label4.Style["top"] = "70px";
                    Panel1.Controls.Add(label4);

                    Label label5 = new Label();
                    label5.ID = "lblMan" + CarID;
                    label5.Text = "Manufacturer: " + Man;
                    label5.ForeColor = System.Drawing.Color.Lime;
                    label5.Style["Left"] = "270px";
                    label5.Style["position"] = "absolute";
                    label5.Style["top"] = "90px";
                    Panel1.Controls.Add(label5);

                    Label label6 = new Label();
                    label6.ID = "lblClass" + CarID;
                    label6.Text = "Class: " + Class;
                    label6.ForeColor = System.Drawing.Color.Lime;
                    label6.Style["Left"] = "270px";
                    label6.Style["position"] = "absolute";
                    label6.Style["top"] = "110px";
                    Panel1.Controls.Add(label6);

                    Label label7 = new Label();
                    label7.ID = "lblType" + CarID;
                    label7.Text = "Type: " + Type;
                    label7.ForeColor = System.Drawing.Color.Lime;
                    label7.Style["Left"] = "270px";
                    label7.Style["position"] = "absolute";
                    label7.Style["top"] = "130px";
                    Panel1.Controls.Add(label7);

                    if (bWinnerID == true)
                    {
                        Label label8 = new Label();
                        label8.ID = "lblWinnerID" + CarID;
                        label8.Text = "WinnerID: " + WinnerID;
                        label8.ForeColor = System.Drawing.Color.Lime;
                        label8.Style["Left"] = "270px";
                        label8.Style["position"] = "absolute";
                        label8.Style["top"] = "130px";
                        Panel1.Controls.Add(label8);
                    }
                    if (bWiningBet == true)
                    {
                        Label label9 = new Label();
                        label9.ID = "lblWinningBet" + CarID;
                        label9.Text = "WinningBet R: " + WinningBet;
                        label9.ForeColor = System.Drawing.Color.Lime;
                        label9.Style["Left"] = "270px";
                        label9.Style["position"] = "absolute";
                        label9.Style["top"] = "130px";
                        Panel1.Controls.Add(label9);
                    }

                    /*int View = s.TimesView(CarID);
                    Label label10 = new Label();
                    label10.ID = "lblView" + CarID;
                    label10.Text = "Times View: " + View;
                    label10.ForeColor = System.Drawing.Color.Lime;
                    label10.Style["Left"] = "1000px";
                    label10.Style["position"] = "absolute";
                    label10.Style["top"] = "130px";
                    Panel1.Controls.Add(label10);*/

                    Button btnView = new Button();
                    btnView.ID = CarID;
                    btnView.Text = "View Car";
                    btnView.ForeColor = System.Drawing.Color.DeepSkyBlue;
                    btnView.BackColor = System.Drawing.Color.Gray;
                    btnView.BorderColor = System.Drawing.Color.Violet;
                    btnView.Style["top"] = "110px";
                    btnView.Style["left"] = "800px";
                    btnView.Style["Height"] = "20px";
                    btnView.Style["position"] = "absolute";
                    btnView.BorderStyle = BorderStyle.Outset;
                    btnView.Click += new EventHandler(this.btnView_Click);
                    GCarID = CarID;
                    Panel1.Controls.Add(btnView);
                }
            }
        }
    }

            void btnView_Click(object sender, EventArgs e)
            {
                Session["CarID"] = GCarID;
                Response.Redirect("View.aspx");
            }

}}

Answer 1

Try add a custom html attribute.

//code behind:

Button btnView = new Button();
btnView.ID = CarID;
//here
btnView.Attributes.Add("GCarID", CarID);
btnView.Text = "View Car";
btnView.ForeColor = System.Drawing.Color.DeepSkyBlue;
btnView.BackColor = System.Drawing.Color.Gray;
btnView.BorderColor = System.Drawing.Color.Violet;
btnView.Style["top"] = "110px";
btnView.Style["left"] = "800px";
btnView.Style["Height"] = "20px";
btnView.Style["position"] = "absolute";
btnView.BorderStyle = BorderStyle.Outset;
btnView.Click += new EventHandler(this.btnView_Click);

//click
void btnView_Click(object sender, EventArgs e)
{
    Session["CarID"] = ((Button)sender).Attributes["GCarID"];
    Response.Redirect("View.aspx");
}

Answer 2

You need to understand the ASP.NET Life Cycle . Your dynamic controls need to be created in the Page_Init() stage, not the Page_Load().

What is happening is you are creating your controls in the Page_Load and when you click on a button and a post back occurs, your dynamic controls are being destroyed. The viewstate for controls is created after the Page_Init, but before the Page_Load. Therefore, your control's that you create dynamically are not keeping their values (such as the ID).

Check out this page and this page for a basic understanding of what I am talking about.

Answer 3

What's the issue? In your event handler btnView_Click(object sender, EventArgs e), the sender would be the button which got clicked. Just cast sender to Control or Button => (sender as Control) or (sender as Button) and retrieve the carID from the ID property.. (which you set in page load) - btnView.ID = CarID;

This is of course assuming your page viewstate is working fine :) - which can be tricky with dynamically added controls in asp.net

Answer 4

You want to use Button's Command event with CommandArgument instead of Click event.

CommandArgument is meant for that kind of storing arguments, and retrieves it back on past back.

Button btnView = new Button();
btnView.ID = CarID;
btnView.Text = "View Car";
btnView.ForeColor = System.Drawing.Color.DeepSkyBlue;
btnView.BackColor = System.Drawing.Color.Gray;
btnView.BorderColor = System.Drawing.Color.Violet;
btnView.Style["top"] = "110px";
btnView.Style["left"] = "800px";
btnView.Style["Height"] = "20px";
btnView.Style["position"] = "absolute";
btnView.BorderStyle = BorderStyle.Outset;
btnView.Command += btnView_Command; // Note: Command event is used instead of Click.
btnView.CommandArgument = CarID; // Note: CarID is stored in CommandArgument.
Panel1.Controls.Add(btnView);

void btnView_Command(object sender, CommandEventArgs e)
{
    string carID = e.CommandArgument.ToString();
    Session["CarID"] = carID;
    Response.Redirect("View.aspx");
}