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table disappears

Posted on 2006-11-08
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Last Modified: 2008-03-17
Hi,

I fill a Table from my code-behind file (C# ASP.NET 2.0) which is supposed to represent a form.

<asp:Table ID="input_table" runat="server" CellPadding=10 GridLines="Both" BackColor = white>
    </asp:Table>

The table is successfully created here:

protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            // create table

            … invoke code to create the table

            Session["input_table"] = this.input_table;
}
else
{

}
}

The table is made persistent as shown above. The page also contains a button. In its OnClick method I would like to access the entries of the user (in the table cells). Unfortunatley, the table disappears  when the button is clicked. I am just wondering why this is and how I can prevent it? Any input would be very much appreciated. Many thanks in advance.

Chris
0
Comment
Question by:csetzkorn
  • 8
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14 Comments
 
LVL 11

Expert Comment

by:ethoths
ID: 17896736
You need to get the table back out of session state in your else clause (if it is a postback).

this.input_table=Session["input_table"]


0
 

Author Comment

by:csetzkorn
ID: 17896753
sorry, I did this but forgot to add it to my post. I seem to be able to access the table in the OnClick method but it disappears.

C
0
 

Author Comment

by:csetzkorn
ID: 17896987
Hi,

It still disappears. Any feedback would be very much appreciate. This is the 'correct code' I am using:

protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
          // create table

          … invoke code to create the table

          Session["input_table"] = this.input_table;
}
else
{
this.input_table = (Table)Session["input_table"];
}
}
0
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LVL 11

Expert Comment

by:ethoths
ID: 17897016
You are creating the tabel in the if clause. Are you also adding it to the pages controls collection here. If so you need to do this in the else clause also. Please send your complete code.
0
 

Author Comment

by:csetzkorn
ID: 17897040
The table already exists in the aspx file

<asp:Table ID="input_table" runat="server" CellPadding=10 GridLines="Both" BackColor = white>
</asp:Table>

In Page_Load I add objects (e.g. TextBox[es]) to the table cells. This works fine. The table is shown like a form with all these elements. When I click this button:

<asp:Button id="validate_entries" Runat="server" Font-Bold="True" Text="Validate Entries" OnClick="validateEntriesClick"></asp:Button>
   
I can still access all the objects in the table within the 'validateEntriesClick' method but the table becomes invisible. The question is why this happens? This:

this.input_table = (Table)Session["input_table"];

does not seem enough to make it reappear. Perhaps I do not fully understand the life cycle of the page but I doubt I have to recreate everything ...

Thanks,

C
0
 

Author Comment

by:csetzkorn
ID: 17897245
If I am using:

protected void Page_Load(object sender, EventArgs e)
{
         // create table

          … invoke code to create the table
}

everything works fine (I even don't lose the data entered by the user???). However, this would be too inefficient wouldn't it as the table is created every time ...??!!

C
0
 
LVL 96

Expert Comment

by:Bob Learned
ID: 17897508
If you are adding the Table dynamically, all dynamic controls need to be recreated on post-back.

Bob
0
 

Author Comment

by:csetzkorn
ID: 17897544
This might be a stupid question. Why can I not put the whole (dyn. created) object (table), which contains all the other objects, and put it in a session object and then (after the postback) do this:

Session["input_table"] = this.input_table;

as I have done before.

Everything works fine if I recreate the table each time after a postback. I am just wondering, why ASP.NET 2.0 is 'clever enough' to restore the values entered by a user (they are still their after a postback).

Thanks.

Christian
0
 
LVL 96

Accepted Solution

by:
Bob Learned earned 1000 total points
ID: 17897554
You can store anything serializable into the Session, but that doesn't mean that it is added to the form through that mechanism.  It needs to be rendered in the output HTML.

Bob
0
 

Author Comment

by:csetzkorn
ID: 17897572
ok thanks. that makes sense.

could you possibly answer the second part of my last question?

Thanks.

C
0
 
LVL 96

Expert Comment

by:Bob Learned
ID: 17897583
If you are storing the Table in the Session, on post back are you recreating the Table, or getting it from the Session variable and rendering that?

Bob
0
 

Author Comment

by:csetzkorn
ID: 17897608
no. I am just doing this:

protected void Page_Load(object sender, EventArgs e)
{
         // create table

          … invoke code to create the table
}

and it works as I wanted. It even persists the values entered by users (e.g. after a refresh). I am just wondering why this is? ASP.NET 2.0 seems to do this automatically which is nice.

Thanks,

Christian
0
 
LVL 11

Expert Comment

by:ethoths
ID: 17897625
Yes asp.net does this automatically. It can even raise echanged events as it knows what the previous values was (from viewstate) and it knows what the new values is (from the post collection).

 
0
 

Author Comment

by:csetzkorn
ID: 17897658
Ok thanks for your feedback. I accept Bob's comment (11/08/2006 04:54AM PST
) as it clarifies things.

Chris
0

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