CODEWITHSUNDEEP
c#asp.net
user1803300
user1803300

Reputation:

Items in Table are gone after a Postback

When ever i hide or show the Panel, the items i add (dynamically) to the Table are gone, and another thing is that when i try add new Row to the Table, it won't show it, it's overwriting the same Row, why ??.

Here's the CodeBehind:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void Button2_Click(object sender, EventArgs e)
        {
            DropDownList1.Items.Add(TextBox3.Text);
        }

        protected void Button3_Click(object sender, EventArgs e)
        {
            if (Panel1.Visible == true)
                Panel1.Visible = false;
        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            if (Panel1.Visible == false)
                Panel1.Visible = true;
        }

        protected void Button4_Click(object sender, EventArgs e)
        {
            TableCell tdStudentName = new TableCell();
            tdStudentName.Text = TextBox1.Text;

            TableCell tdStudentCourse = new TableCell();
            tdStudentCourse.Text = DropDownList1.SelectedValue;

            TableCell tdStudentGrade = new TableCell();
            tdStudentGrade.Text = TextBox2.Text;

            TableRow tr = new TableRow();
            tr.Cells.Add(tdStudentName);
            tr.Cells.Add(tdStudentCourse);
            tr.Cells.Add(tdStudentGrade);

            Table1.Rows.Add(tr);
        }
    }
}

Here's the Html Source:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="WebApplication1.WebForm1" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>

        <asp:Label ID="Label1" runat="server" Text="Student Name:"></asp:Label>
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <br />
        <asp:Label ID="Label2" runat="server" Text="Course:"></asp:Label>
        <asp:DropDownList ID="DropDownList1" runat="server">
        </asp:DropDownList>
        <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Add Course" />
        <br />
        <asp:Label ID="Label3" runat="server" Text="Grade:"></asp:Label>
        <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
        <asp:Button ID="Button4" runat="server" OnClick="Button4_Click" Text="Add" />
        <br />
        <br />
        <asp:Panel ID="Panel1" runat="server" GroupingText="Course Settings" Visible="False">
            <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
            <asp:Button ID="Button2" runat="server" OnClick="Button2_Click" Text="Add" />
            <asp:Button ID="Button3" runat="server" OnClick="Button3_Click" Text="Close" />
        </asp:Panel>
        <br />
        <br />
        <asp:Table ID="Table1" runat="server" BorderStyle="Solid">
            <asp:TableRow runat="server">
                <asp:TableCell runat="server">Name</asp:TableCell>
                <asp:TableCell runat="server">Course</asp:TableCell>
                <asp:TableCell runat="server">Grade</asp:TableCell>
            </asp:TableRow>
        </asp:Table>

    </div>
    </form>
</body>
</html>

Here's a preview of how it looks like:

enter image description here

Upvotes: 1

Views: 981

Answers (1)

freefaller
freefaller

Reputation: 19953

If you add anything dynamically, then you must re-add it on any subsequent post-back. They will not automatically just "be there" on the next post-back.

This requires you to store the fact that the dynamic controls have been created and added, and therefore allows you to detect that on the post-back and add the controls back in again.

It is better (if possible) to add dynamic controls as part of the init stage of the life cycle, as this will mean they will pick up view state information before the load stage.

Edit

In response to the comment by the OP...

Where do i store these controls ? and where do i add them back ? inside Page_Load ?

You don't store the controls... you store the fact that the controls have been added.

The "easiest" way would be to use the ViewState, but that puts you in a catch-22 situation... because the ViewState is not available at the init stage of the life cycle, which is the preferred place to re-add those controls.

Another option would be to "store the fact" within an <asp:HiddenField> which you can check for within the init stage. However you would have to get the value directly from the Request object, as the field would not have the correct .Value at the init stage. You'd do that like...

if (!Page.IsPostBack)
{
   string hdnValue = Request[hdnFieldCtrl.UniqueId];
   // Recreate controls based on the details you need
}

Upvotes: 1

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