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How to maintain Listbox position after Postback

Posted on 2007-12-03
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Last Modified: 2012-06-21
Greetings

I have a listbox that contains names. AT this point all I want to do si display the current item in a text box.

As I understand things (which stands a fair chance of being wrong!!), in order to see the change effected to the textbox, the AutoPostBack property must be set to TRUE, to foirce a PostBack after selection change. This I have done, but am getting the following:

A potentially dangerous Request.Form value was detected from the client (TextBox1="...>>Mickey<<<PL").

WHAT SHOULD I BE DOING??
(IT ALSO LOOKS LIKE THE POSITION IN THE LISTBOX IS BEING LOST ON POSTBACK!!)

My code:

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            ListBox1.Items.Add("Mickey");
            ListBox1.Items.Add("Donald");
            ListBox1.Items.Add("Goofy");
            ListBox1.Items.Add("Wacko");
            ListBox1.SelectedIndex = 0;
        }
       
        TextBox1.Text = ">>>" + ListBox1.SelectedValue + "<<<PL";
    }
   
    protected void ListBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        Label1.Text = ">>>" + ListBox1.SelectedValue + "<<<SI";
    }
    protected void ListBox1_TextChanged(object sender, EventArgs e)
    {
        Label1.Text = ">>>" + ListBox1.SelectedValue + "<<<ST";
    }

In advance, thanks!!
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Question by:allanmark
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5 Comments
 
LVL 37

Accepted Solution

by:
samtran0331 earned 1200 total points
ID: 20395715
>>A potentially dangerous Request.Form value was detected from the client

this is happening because .Net detects that the textbox contains the "<" and the ">" characters....which can be used for sql/script injection attacks.

while you can turn the warning off, you lose a level of hack protection.
0
 
LVL 14

Assisted Solution

by:Dustin Hopkins
Dustin Hopkins earned 300 total points
ID: 20395757
You could use the html encoded values for >(&gt;) and <(&lt;) in your code.

Label1.Text = "&gt;&gt;&gt;" + ListBox1.SelectedValue  + "&lt;&lt;&lt;PL";

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0
 
LVL 37

Assisted Solution

by:samtran0331
samtran0331 earned 1200 total points
ID: 20395802
that would work for a label, but .Net is catching the tags when the code does this:

TextBox1.Text = ">>>" + ListBox1.SelectedValue + "<<<PL";

and setting a textbox text to "&gt;" will still render "&gt;"
0
 

Author Comment

by:allanmark
ID: 20396170
Short and sweet  -  Thank You very much!!!
0
 

Author Closing Comment

by:allanmark
ID: 31412334
Most educational -  thank you!!
0

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