Develop Reference

Using ASP.NET to Hide an HTML Div

I am using ASP.NET for a web page in order to make some server calls that involve looking up user organization information. Based on that information, we need to either hide or display a div. In the header I have a C# function that definitely runs. I have tried the following lines to hide the div.
divID.Style.Add("display","none");
and
divID.Visible = false;
In the body, I am currently using an asp:Panel that runs at server and contains the id "divID". No matter what I do, I can't get the div to hide (without manually putting the styling in). I tried putting the scripts before and after the body, and it didn't make a difference. Any suggestions on the best way to do this would be appreciated.
EDIT:
Here is the C# initiating code.
<script runat="server" language="C#">
void getUserInfo(Object sender, EventArgs ev){
The rest of the C# code is irrelevant, but the relevant line shown above is definitely being run.
The HTML portion looks something like this.
<asp:Panel runat="server" id="divID" style="width:200px; height:130px; ">
<div style="text-align:center">Test Data</div>
</asp:Panel>

C# code is always compiled and run from the server-side, and so cannot impact the state of a page once rendered unless you use postbacks or callbacks. If you want to change the visible state of a control on the client-side, you will need to use Javascript on the client side (possibly triggered by a button click) to show and hide the control.
As an example, check out the solution at the link below.
https://forums.asp.net/t/1603211.aspx?Show+hide+div+on+button+click+without+postback
<script type="text/javascript">
function ToggleDiv(Flag) {
if (Flag == "first") {
document.getElementById('dvFirstDiv').style.display = 'block';
document.getElementById('dvSecondDiv').style.display = 'none';
}
else {
document.getElementById('dvFirstDiv').style.display = 'none';
document.getElementById('dvSecondDiv').style.display = 'block';
}
}
</script>
<asp:Button ID="btn" runat="server" Text="Show First Div"
OnClientClick="ToggleDiv('first');return false;" />
<asp:Button ID="Button1" runat="server" Text="Show Second Div"
OnClientClick="ToggleDiv('second');return false;" />
<br />
<div id="dvFirstDiv" style="display: none;">
First Div
</div>
<div id="dvSecondDiv" style="display: none;">
Second Div
</div>

In the header I have a C# function that definitely runs.
If you're talking about the HTML page header - no, it definitely not running. C# code is executed only server side.
Based on your post, I'm assuming we're talking WebForms here and yo have a script block in your aspx file. While this is fine, I recommend placing the server-side code into a code behind file.
So all you need to do is to add a handler for the PreRender phase of the page life cycle and place your logic for showing/hiding the div in there.
public void Page_Prerender(object sender, EventArgs e)
{
divID.Visible = false;
' OR
'divID.Style.Add("display","none");
}
Note that setting the Visible property of a WebForms control excludes the control from rendering to the page, whilst setting display: none renders it as HTML but it isn't displayed on the page.

Try in backcode: divID.Controls.clear();
This worked for me.

best practices for dynamic content

I have a pretty extensive Classic ASP background (using server-side javascript), and my company is finally (FINALLY) making the push towards recoding everything in ASP.Net (using C#). I have a good grasp on good programming practices in Classic ASP and I usually try to make sure I code things the "right" way. I've been reading ASP.Net tutorials and feel like I have a pretty understanding of the basics. I have good discipline about separating client side javascript into external js files, keeping styling outside of the markup in external css files, etc. So, when reading these novice tutorials I understand the concept of the code-behind pages. It makes sense to me to separate the c# code from what will ultimately become the markup for the page. Making < asp:button > objects and the code-behind rules to alter them makes perfect sense.
However, I'm having a hard time wrapping my head around how to do something simple like I would have done in Classic ASP like this:
<%
if (condition) {
%>
<input type="button" value="click me" onclick="dosomething()" />
<%
}
else {
%>
<span>You don't have permission to see the button</span>
<%
}
%>
I'm having a hard time trying to figure out how I'm supposed to fit the conditional stuff you see above into the code-behind page. If I was showing a button under both circumstances, I'd make an <asp:button> object and style it in the code-behind page accordingly - but in the example above I'm only showing the button if the condition is true, and a span block if false.
I know that you don't HAVE to put ALL the c# code in the code-behind page. I can use the <% %> tags the same way I would do in Classic ASP. But, if I do that then it seems to me that it lessens the relevance of the code-behind page. For example, I know you can use an external css stylesheet to stylize your page and at the same time use inline styles on individual tags as well. I believe this to be poor practice, however. It makes it difficult to later have to adjust the styles on that element if you don't know whether to look in the markup or in the css file to find the relevant styles affecting that element.
It seems to me that the same would hold true for your markup and code-behind pages. Is it just a necessary evil to have to mix the 2, or is there a better way to do what I'm demonstrating above?

You could have in your markup:
<asp:Button .. Visible="False" />
<asp:Label .. Text="You do not have permissions" Visible="False" />
Note the Visible property. ASP.NET web forms is build on the idea of an object model, so the button and label are objects you can work with. In the code behind, you can have:
protected void Page_Load(object sender, EventArgs e) {
.
.
if (Xcondition = true) {
Button1.visible= true;
Label2.Visible = false;
}
else {
Button1.visible= false;
Label2.Visible = true;
}
}
Is the traditional way to accomplish this. You just have to figure out where in the lifecycle you need to do this, as load may not be the best (Init or PreRender event, for instance). If you only need to do this at startup once, do if (!Page.IsPostBack) { .. } to ensure it only runs once.

I made a small example that you can basically just copy/paste and mess around with a little.
This is the aspx code:
< body>
<form id="form1" runat="server">
<div>
<asp:TextBox runat="server" ID="txtCondition"></asp:TextBox>
<asp:Button runat="server" Text="Check condition" ID="btnCheckCondition" OnClick="btnCheckCondition_Click" />
<asp:Button runat="server" Text="Click me" ID="btnSubmit" OnClick="btnSubmit_Click" Visible="false"/>
<asp:Label runat="server" ID="lblMsg"></asp:Label>
</div>
</form>
</body>
this is the code behind: (if you double click on the btnCheckCondition, the click_event method will be automatically generated in your codebehind.
protected void btnCheckCondition_Click(object sender, EventArgs e)
{
if (txtCondition.Text == "Show the button")
{
btnSubmit.Visible = true;
lblMsg.Text = "You are allowed to see the button.";
}
else
{
lblMsg.Text = "You are NOT allowed to see the button.";
}
}
This will basically check the input in the textbox txtCondition. If it is equal to "Show the button", the second button will become visible. If the text is something else, the button will not appear and a label will say that you are not allowed to see the button.

have a label and a button in the page. check the condition from code behind and based on the condition, hide or show the control. you can use visibility attribute of the controls to hide or show them. Also use asp.net controls so that you can access them from code behind.

Unless you have a good reason not to, use the Visible property. (In ASP.NET Web Forms, you're asking for trouble if you change the structure of the component tree dynamically other than using repeater controls.) What I do is:
Page.aspx
<button type='button' Visible='<%# condition %>' runat='server'>
Click Me!
</button>
<span Visible='<%# !condition %>' runat='server'>
No button for you!
</span>
Page.aspx.cs
protected void Page_Load() {
if (!IsPostBack) DataBind(); // evaluates <%# ... %> expressions
}
(My preference is to make controls to "pull" data from code-behind instead of pushing it there, and use anonymous and plain HTML controls over their heavier equivalents when possible.) Any way of setting Visible before the page renders will work though.

First to help you with the easy way, to been able the condition to been recognized you need to define it and make it public on code behind. For example:
<%if (condition) {%>
<input type="button" value="click me" onclick="dosomething()" />
<%}else { %>
<span>You don't have permission to see the button</span>
<% } %>
and on code behind
public partial class OnePage : System.Web.UI.Page
{
public bool condition = false;
protected void Page_Load(object sender, EventArgs e)
{
// here change the condition
}
}
Second case with function call
<%if (fCheckAuth()) {%>
<input type="button" value="click me" onclick="dosomething()" />
<%}else { %>
<span>You don't have permission to see the button</span>
<% } %>
and on code behind
public partial class OnePage : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
public bool fCheckAuth()
{
// return your evaluate
return false;
}
}
More asp.net form style
Now, working with the new asp.net (compared with the classic asp) you can also do that (and similar to that).
<asp:Panel runat="server" ID="pnlShowA">
<input type="button" value="click me" onclick="dosomething()" />
</asp:Panel>
<asp:Panel runat="server" ID="pnlShowB">
<span>You don't have permission to see the button</span>
</asp:Panel>
Use one asp:Panel to warp your full content, and on code behind you open it and close it.
public partial class OnePage : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (condition)
{
pnlShowA.Visible = true;
pnlShowB.Visible = false;
}
else
{
pnlShowA.Visible = false;
pnlShowB.Visible = true;
}
}
}

While the question is not about using ASP.NET Web Forms versus ASP.Net MVC. I felt compelled to point out that it may be more beneficial going with ASP.NET MVC rather than ASP.NET Web Forms in your scenario.
I say this because Classic ASP and ASP.NET MVC inline style is similar. In most cases you could probably convert ASP (<% %>) to Razor(a different flavor of in-lining server-side code with HTML) with little modification to the underlining logic. I don't know about you but the less code I have to write the better. For example, your above code would convert to the following Razor syntax:
#if (condition) {
<input type="button" value="click me" onclick="dosomething()" />
}
else {
<span>You don't have permission to see the button</span>
}
To answer your question, I would disable the button on the server-side. Have a disabled on the client. In the case the button is disabled, enable the Label with the appropriate text.
//Code-behind
bool correctPermission = true;
submit.Enabled = correctPermission;
noPermissionMessage.Enabled = !correctPermission;
//Client Code
<asp:Button ID="submit" runat="server" Text="Click Me" />
<asp:Label ID="noPermissionMessage" runat="server" Text="You don't have permission to see the button" Enabled="false" />

Handle every user input as plain text

We have a really big web-application.
About 120.000 lines in total.
In this application the user has plenty possibilities to enter text.
In the user information, folders, groups and so on.
Some of the users want to name different objects like Age < 20.
There was a problem because ASP.NET blocks such input because of the "<" to prevent javascript-injections.
We found a way to shut those safety-mechanisms down but now our application is unsafe.
So the question is:
Is there any setting or property or whatever that can be set global (at one point for the whole application) that the application handles such input as plain text?
So when a user for example wants to name a folder <script>alert("ALERT");</script> it should be named that way and is shown just as <script>alert("ALERT");</script> but the script will not execute.
The same for HTML: if its named Folder<br>One it should look like: Folder<br>One and not like:
Folder
One
Of course i could use HTML-Encode/-Decode but i dont want to go through the whole project and add an Encoding/Decoding wherever an input is made or shown...
Also would a global solution pretent mistakes in the future development.
So again the Question: is there any way to handle every text just as text? And all that as global as possible?
Hope you could understand my problem and know any possibilities.

If you are using JQuery, whenever you set your value to any span or div,
Use:
$('#myDiv').text('<script>alert("a")</script>');
And Don't use:
$('#myDiv').html('<script>alert("a")</script>');
or
$('#myDiv').innerHTML='<script>alert("a")</script>';

if you dont want to use HTML encode decode than try ValidateRequest="false" You can do it like in code bellow:
<%# Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" ValidateRequest="false" Inherits="_Default" %>
Another technique you may want to use is as following..
<script>
function Encode() {
var value = (document.getElementById('TextBox1').value);
value = value.replace('<', "<");
value = value.replace('>', ">");
document.getElementById('TextBox1').value = value;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="Encode()" />
</form>
Server-Side
protected void Page_Load(object sender, EventArgs e)
{
this.TextBox1.Text = Server.HtmlDecode(this.TextBox1.Text);
}

Adding OnClick event to ASP.NET control

i would like to create OnClick event for my panel. So far now the most of the google results look more or less like this: adding onclick event to aspnet label. Is there any way, to call codebehind function from javascript or panel attributes? Because I would like to Redirect user to a new page and before that save some information in ViewSTate or Sessionstate. Any suggestions?

In your java script method raise a __dopostback call to a Server side method.
<script type="text/javascript">
function YourFunction()
{
__doPostBack('btnTemp', '')
}
</script>
Where btnTemp is a server side button, so write a onClick event of this button on server side, where you can do the processing and then redirect to other page.
You can have a good understanding of dopostback at DoPostBack Understanding

My aspx page is like:
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<script type="text/javascript">
function CallMe() { __doPostBack('btnTemp', '') }
</script>
</head>
<body>
<form id="form1" runat="server">
<asp:Button ID="btnTemp" runat="server" Text="Test" onclick="btnTemp_Click" />
<div> <asp:Label ID="Label1" runat="server" Text="Label1"></asp:Label>
<asp:Label ID="Label2" runat="server" Text="Label"></asp:Label></div>
</form>
</body>
And my Server Side code is as:
protected void Page_Load(object sender, EventArgs e)
{
Label1.Attributes.Add("onClick", "CallMe();");
}
protected void btnTemp_Click(object sender, EventArgs e)
{
}
Thats the code that I have written, I haven;t included the using statement, Page directive etc in above code.

There is a PostBackUrl property on a ASP.NET Button, you could render the button as normal then postback to a different page - this is where your OnClick method would need to be declared.
I would strongly recommend against posting back to the same page then doing a Response.Redirect(), consider the traffic. The browser requests the page, posts back then is sent a HttpRedirect and then navigates to the new page. With the method I have outlined above this is not required and the browser has to make one request less (meaning the message doesn't have to be sent or the page rebuilt on the server) and is a significant performance benefit.

TextBox AutoPostBack pre-empts further events

In a simple ASP page, TextBox AutoPostBack events will prevent Button click events (except where button is tapped very quickly) and AutoPostBack events for other controls (like ListBox).
There's a similar question here, but I wasn't happy with being forced to use client side or AJAX solutions: Have to click button twice in asp.net (after autopostback textbox)
Example ASPX page:
<%# Page Language="C#" AutoEventWireup="true" CodeFile="temp.aspx.cs" Inherits="temp" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:TextBox ID="TextBox1" runat="server" AutoPostBack="True" OnTextChanged="PostBack"></asp:TextBox>
<asp:Button ID="Button1" runat="server" OnClick="PostBack" Text="Button" /><br />
<asp:ListBox ID="ListBox1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="PostBack">
<asp:ListItem>value1</asp:ListItem>
<asp:ListItem>value2</asp:ListItem>
</asp:ListBox><br />
<br />
Events Fired:<br />
<asp:TextBox ID="TextBox2" runat="server" Height="159px" TextMode="MultiLine" Width="338px"></asp:TextBox></div>
</form>
</body>
</html>
C# code behind:
public partial class temp : System.Web.UI.Page
{
protected void PostBack(object sender, System.EventArgs e)
{
this.TextBox2.Text += string.Format("PostBack for - {0}\n", ((System.Web.UI.Control)sender).ID);
}
}
I've been able to partially solve this problem for buttons by using mousedown instead of click events to submit the form (I also blocked extra AutoPostBack events client-side and handled any extra field changes during button click events server side)
However, this means my buttons aren't quite behaving in the standard (click on release) way.
Is there a better solution to this problem that doesn't require trying to do everything in javascript client-side? (I'm writing a lot of code that reads server data during these postbacks, so javascript isn't an ideal solution.)
I'm also trying to avoid switching to an AJAX library for these pages since every new library I add has to go through security auditing etc.
Note: I'm currently working with ASP.Net 2.0/VS 2005, but if this type of problem is fixed in a later release that would be a compelling argument to upgrade. (As far as I understand it, the same problem seems to happen in ASP.Net 4/VS 2010)

The reason to set AutoPostBack="true" on a field (or other input control) is because you want the page to postback when that control's data changes - without requiring that the user click a button. It sounds like that is exactly what is happening: when the field loses focus, the page does a postback.
Perhaps I'm misunderstanding the question? Can you provide some more information about how you need the page/form to behave?
Edit: more info, based on comment from OP.
I think I understand: the "normal" case is they select something from a DropDownList1, and you autopostback to set the values of DropDownList2, based on the selected item in DropDownList1. However, the user may not care about the second list; if they click "search", you want the button-click to essentially abort the autopostback (already in progress), and initiate a new postback.
Unfortunately, I don't think there's any functionality in any version of ASP.NET to "abort" a postback already in progress (not from the client-side code, anyway). Therefore, in order to implement the above behavior, you're going to have to do something outside the standard ASP.NET postback behavior. Here's a few ideas, though by no means is it an exhaustive list:
Use AJAX and JS to retrieve the contents of DropDownList2. If the user clicks search while that ajax call is in progress, the page should postback right away.
Store all possible DropDownList2 data in JSON format in your page; use purely client-side JS to populate List2 when List1 changes. Again, if the user clicks "search", the page will postback right away. Depending on how big the pool of possible List2 entries is, this may bloat the page size too much to be workable.
Use client-side JS to disable your search button when List1 changes selection. The user won't be able to click "search" until the autopostback (to fill List2) completes.
Hope this helps!

To make the client side be more interactive and reduce sending all that viewstate and redrawing the page, I add a little jquery into the mix. It makes things like what you are proposing possible. jquery even ships with the asp.net MVC framework so there is no shame in using it with asp.net.
Here is a simple example that uses jquery that demonstrates what I think you want.
First, in the aspx file, add in a reference to the jquery library. I use the
Google content delivery network so you don't even have add this file to your VS project.
Then take the auto postback references out of all your server controls except the button. I left that one to continue doing a postback because I suspect at some point you want a regular post back, all the other controls use ajax to get your server side response.
I started by using your example page with these modifications:
<%# Page Language="C#" AutoEventWireup="true" CodeBehind="temp.aspx.cs" Inherits="temp" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Untitled Page</title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js" type="text/javascript"></script>
</head>
<body>
<script type="text/javascript">
$(document).ready(function () {
// Establish where the output goes.
var outputObject = $("#<%=TextBox2.ClientID %>");
// create a function to do an ajax postback
function doAjaxPostback(sender, value) {
$.ajax({
type: "POST",
url: "temp2.aspx",
data: "id=" + sender.attr("id") + "&value=" + value,
success: function (data) { outputObject.append("<br />" + data) }
});
}
// Use jquery to wire up the event handler. We use the ClientID property in case these
// elements get embeded in some other server control container later.
$("#<%=TextBox1.ClientID %>").keyup(function (event) { doAjaxPostback($(this), $(this).val()); });
$("#<%=TextBox1.ClientID %>").change(function (event) { doAjaxPostback($(this), $(this).val()); });
$("#<%=ListBox1.ClientID %>").change(function (event) { doAjaxPostback($(this), $(this).val()); });
// Use a plain html button tag for ajax only. The server control button gets rendered as
// a submit button which requires it to be handled a little differently.
$("#PlainButton").click(function (event) { doAjaxPostback($(this), $(this).attr("value")); event.preventDefault(); });
});
</script>
<form id="form1" runat="server">
<div>
<asp:TextBox ID="TextBox1" runat="server" ></asp:TextBox>
<asp:Button ID="Button1" runat="server" OnClick="PostBack" Text="Button" /><br />
<button id="PlainButton" value="Plain Old Button">Ajax Only, No postback</button>
<br />
<asp:ListBox ID="ListBox1" runat="server" >
<asp:ListItem>value1</asp:ListItem>
<asp:ListItem>value2</asp:ListItem>
</asp:ListBox>
<br />
<br />
Events Fired:<br />
<asp:TextBox ID="TextBox2" runat="server" Height="159px" TextMode="MultiLine" Width="438px"></asp:TextBox>
</div>
</form>
</body>
</html>
Then for the code behind I just made a tiny change so we can report when we get a regular postback versus the ajax kind:
protected void PostBack(object sender, System.EventArgs e)
{
this.TextBox2.Text += "\n\nGot an asp.net postback\n\n"
+ string.Format("PostBack for - {0}\n", ((System.Web.UI.Control)sender).ID);
}
Okay, so I was trying not to get too fancy but I wanted to demonstrate how easy this is so I made a second page, temp2.aspx but left the aspx file alone as i only needed what is in the code behind:
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 temp2 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
string id = string.Empty;
string value = string.Empty;
Response.Clear();
if (Request.Form == null || Request.Form.Count < 1)
{
Response.Write("I got nothin'");
Response.Flush();
Response.End();
return;
}
id = Request.Form["id"];
value = Request.Form["value"];
Response.Write(string.Format("\nevent from: {0}; value={1}",id,value));
Response.Flush();
Response.End();
}
}
}
Notice that what I did was clear, write, flush and end the response so only the text we want is sent back to the caller. We could have done some fancy stuff in the page_load of the original temp page to check if it is a call from the ajax function that will not clear or flush the response if the incoming Request.Form does not contain a certain field, etc. But by doing it as a separate page, I hoped to simplify the code. This also opens up possibilities.
Say you have a country drop down that has Canada and USA in it and when it changes, you want to sent back data to populate a State/Province dropdown with the appropriate values. By putting the lookup code on its own page the way I did with temp2.aspx, you can then call it from all the pages in your app that have a need for such a service.
Good luck, let me know if you have any trouble understanding my code.