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Unable to modify the control collection

I'm trying to add a Link to a webform page from a user control. The CSS file contains the styling used by the control. When I try, I get the following exception:
The control collection cannot be modified during DataBind, Init, Load,
PreRender or Unload phase
So, when can anything be added to the controls collection? Seems to me the exception message suggests that all options are off the table. Here's the code:
public partial class AddNoteDlg : UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
RegisterFiles();
}
private void RegisterFiles()
{
Page.ClientScript.RegisterClientScriptInclude(GetType(), "addNoteDlgComponent-1.0.0.js", ResolveUrl("~/Shared/scripts/js/addNoteDlgComponent-1.0.0.js"));
var css = new HtmlLink();
css.Href = ResolveUrl("~/Shared/css/addNoteDlg-0.0.1.css");
css.Attributes["rel"] = "stylesheet";
css.Attributes["type"] = "text/css";
css.Attributes["media"] = "all";
Page.Controls.Add(css);
}
}

Instead, stuck the link tag in the user control markup, as there is no difference, practically speaking.
(The original motivation for doing it programmatically was so I could add it to the header, with Page.Header.Controls.Add(css), allowing me to keep all CSS links in the header.)

Get selected feature attributes in GeckoFx

I am using GeckoFx in my windows form app. When I select a feature in Gecko it should fill the attributes attr1 and attr2 of 'selectedfeature' class based on geojson file that loaded to html file. I test that html file and when clicking a feature this attributes will be filled (with javascript code).
<div class="selectedfeature" attr1="attr1" attr2="attr2"></div>
and when I want to retrieve these attributes from Gecko in 'geckoWebBrowser_DomClick' event, this event is raised first and so attributes attr1 and attr2 will be empty.
I used another events but nothing happened.
Any suggestion?

I moved the contents of 'geckoWebBrowser_DomClick' to another method 'DomClicked()' and this method called again when I get a property (SelectedFeature) that its value should be filled with attr1 or attr2.
private void geckoWebBrowser_DomClick(object sender, Gecko.DomMouseEventArgs e)
{
DomClicked();
}
private string _selectedFeature;
public string SelectedFeature
{
get
{
GBDomClick();
return _selectedFeature;
}
private set { _selectedFeature= value; }
}
By this (second called of DomClicked()),
<div class="selectedfeature" attr1="attr1" attr2="attr2"></div>
are filled with click event of javascript code. But in the first call:
<div class="selectedfeature" attr1="" attr2=""></div>
click event of javascript code does not execute.

How to open multiple windows on a button click?

In my design there are three buttons. I want to open new windows on each button click. I have done upto open a new window. But when I click on the second button it opens in the same popup window. How can I avoid this and open three windows when click on these three buttons?
c# code
protected void btnApprove_Click(object sender, EventArgs e)
{
string ddlVal = ddlComp.SelectedValue.ToString();
if (ddlVal != "--Select The Competition--")
{
Session["ddlVal"] = ddlComp.SelectedValue.ToString();
ScriptManager.RegisterStartupScript(this, typeof(string), "APPROVE_WINDOW", "var Mleft = (screen.width/2)-(760/2);var Mtop = (screen.height/2)-(700/2);window.open( 'approved.aspx', null, 'resizable=yes, status=yes,toolbar=no,scrollbars=yes,menubar=no,location=no,top=\'+Mtop+\', left=\'+Mleft+\'' );", true);
}
else
{
WebMsgBox.Show("Select a competition");
}
}
This is the code I have used for all the three buttons with different page names

You can pass the name parameter as '_blank' instead of null.
Change the below line in your code
window.open( 'approved.aspx', null,
to
window.open( 'approved.aspx', '_blank',

If you're referring to top-level browser windows, you cannot - browsers disable this for obvious reasons (pop-up blockers, etc). You also cannot have more than one JavaScript alert() window open at a time.
Your WebMsgBox class wraps the alert() function. So this not possible.
You will need to change your client-code to instead display multiple elements (e.g. absolutely-positioned <div> boxes with a modal rectangular appearance).

Post to facebook group with C# code

I am working on a windows application where I embedded webbroswercontrol. I am trying to post sample message to a open facebook group. I am unable to change value of a textbox with c#. When ever I automate click it says textbox value is null. What would be the fix?
<input type="hidden" autocomplete="off" class="mentionsHidden"
name="xhpc_message" value="lklklkl">
HtmlElement textBox = this.FindControlByName("xhpc_message",
this.webBrowser.Document.All);
//Click Code
var elements = webBrowser.Document.GetElementsByTagName("button");
foreach (HtmlElement element in elements)
{
// If there's more than one button, you can check the
//element.InnerHTML to see if it's the one you want
if (element.InnerText.Contains("Post"))
{
if (textBox.InnerText.Trim() == "Write something...")
{
textBox.Focus();
textBox.GetAttribute("value").Equals("Test Message");
IHTMLElement nativeElement = element.DomElement as IHTMLElement;
nativeElement.click();
break;
}
}
}

1) I suggest you to ensure, that textbox is null, not the textBox.InnerText. Usually inner text for elements is null, so its better to check the "placeholder" attribute and update the code with:
// if (textBox.InnerText.Trim() == "Write something...")
if (textBox.GetAttribute("placeholder") == "Write something...")
2) This code doesn't set the value. It gets the value and compares to "Test message".
textBox.GetAttribute("value").Equals("Test Message");
Just use SetValue instead.
textBox.SetAttribute("value", "Test message");
3) Ensure, that all operations are made after page is loaded.
public SomeFormName()
{
...
webBrowser.DocumentCompleted += webBrowser_DocumentCompleted;
}
void webBrowser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs args)
{
// put your code here
}
4) Not sure, how the FindControlByName is working, so check a simple LINQ query to ensure that textbox is found.
var textbox = webBrowser.Document.All.OfType<HtmlElement>()
.Where(item => item.Name == "xhpc_message")
.FirstOrDefault()
;

Use the code below after the Document complete event has been fired completely in a separate function, after commenting your code.The URL in the webbrowser should be holding the Group Page on which the post is to happen.
private void AfteDocumentLoads()
{
HtmlElementCollection textBox = webBrowser.Document.GetElementsByTagName("textarea").GetElementsByName("xhpc_message");
HtmlElementCollection button = webBrowser.Document.GetElementsByTagName("button");
foreach (HtmlElement element in textBox)
{
foreach (HtmlElement btnelement in button)
{
if (btnelement.InnerText == "Post")
{
element.Focus();
element.InnerText = txtPortalUserId.Text.ToString();
btnelement.InvokeMember("Click");
}
}
}
}
I was also stuck as it was not posting earlier because I was using WebBrowser class to get current WebBrowser. Result was that the text was inputted to the Group as a 'dim' Comment. Even if I clicked manually on FB page it would say "This status update appears to be blank. Please write something or attach a link or photo to update your status."
I used the page's webbrowser & it worked cos' it came in proper manner on the page. Also little bit of changes are there in the LOCs

How to check whether postback caused by a Dynamic link button

I have a button control. On click of this button I need to add a Link Button dynamically. The Link Button needs an event handler. Hence the dynamic Link button is first added in the Page_Load and cleared and added again in the button click handler. Please read Dynamic Control’s Event Handler’s Working for understanding the business requirement for this.
I have read On postback, how can I check which control cause postback in Page_Init event for identifying the control that caused the postback (inside Page_Load). But it is not working for my scenario.
What change need to be done to confirm whether the postback was caused by link button (inside Page_Load)?
Note: Refer the following for another scenario where it is inevitable https://codereview.stackexchange.com/questions/20510/custom-paging-in-asp-net-web-application
Note 1: I need to get the postback control ID as the first step inside if (Page.IsPostBack). I need to add the dynamic link buttons control only if it is a postback from the button or the link button. There will be other controls that causes postback. For such postbacks we should not execute this code.
Note 2: I am getting empty string for Request["__EVENTARGUMENT"] in the Page_Load
Related Question: By what event, the dynamic controls will be available in the Page (for using in FindControl). #Tung says - "Your GetPostBackControlId method is properly getting the name of the control that caused the postback, but it is unable to find a control with that id through page.FindControl because the linkbutton has not been created yet, and so page does not know of its existence. "
ASPX
<%# Page Language="C#" AutoEventWireup="true" CodeFile="PostbackTest.aspx.cs" Inherits="PostbackTest"
MasterPageFile="~/TestMasterPage.master" %>
<asp:Content ID="myContent" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
<div id="holder" runat="server">
</div>
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="TestClick" />
</asp:Content>
CODE BEHIND
public partial class PostbackTest : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if(Page.IsPostBack)
{
string IDValue = GetPostBackControlId(this.Page);
int x = 0;
holder.Controls.Clear();
LinkButton lnkDynamic = new LinkButton();
lnkDynamic.Click += new EventHandler(LinkClick);
lnkDynamic.ID = "lnkDynamic123";
lnkDynamic.Text = "lnkDynamic123";
holder.Controls.Add(lnkDynamic);
}
}
protected void TestClick(object sender, EventArgs e)
{
holder.Controls.Clear();
LinkButton lnkDynamic = new LinkButton();
lnkDynamic.Click += new EventHandler(LinkClick);
lnkDynamic.ID = "lnkDynamic123";
lnkDynamic.Text = "lnkDynamic123";
holder.Controls.Add(lnkDynamic);
}
protected void LinkClick(object sender, EventArgs e)
{
}
public static string GetPostBackControlId(Page page)
{
if (!page.IsPostBack)
{
return string.Empty;
}
Control control = null;
// First check the "__EVENTTARGET" for controls with "_doPostBack" function
string controlName = page.Request.Params["__EVENTTARGET"];
if (!String.IsNullOrEmpty(controlName))
{
control = page.FindControl(controlName);
}
else
{
// if __EVENTTARGET is null, the control is a button type
string controlId;
Control foundControl;
foreach (string ctl in page.Request.Form)
{
// Handle ImageButton they having an additional "quasi-property" in their Id which identifies mouse x and y coordinates
if (ctl.EndsWith(".x") || ctl.EndsWith(".y"))
{
controlId = ctl.Substring(0, ctl.Length - 2);
foundControl = page.FindControl(controlId);
}
else
{
foundControl = page.FindControl(ctl);
}
if (!(foundControl is Button || foundControl is ImageButton)) continue;
control = foundControl;
break;
}
}
return control == null ? String.Empty : control.ID;
}
}
REFERENCE
On postback, how can I check which control cause postback in Page_Init event
Dynamic Control’s Event Handler’s Working
Understanding the JavaScript __doPostBack Function
Access JavaScript variables on PostBack using ASP.NET Code
How does ASP.NET know which event to fire during a postback?
how to remove 'name' attribute from server controls?
How to use __doPostBack()

A postback in asp.net is done by the java script function __doPostback(source, parameter)
so in your case it would be
__doPostback("lnkDynamic123","") something like this
So in the code behind do the following
var btnTrigger = Request["__EVENTTARGET"];
if(btnTrigger=="lnkDynamic123")
{
}
--- this would tell that it is your linkbutton that causes the postback

You can move the call to the GetPostBackControlId method after the LinkButton has been added to the page:
protected void Page_Load(object sender, EventArgs e)
{
if (Page.IsPostBack)
{
holder.Controls.Clear();
LinkButton lnkDynamic = new LinkButton();
lnkDynamic.Click += new EventHandler(LinkClick);
lnkDynamic.ID = "lnkDynamic123";
lnkDynamic.Text = "lnkDynamic123";
holder.Controls.Add(lnkDynamic);
string IDValue = GetPostBackControlId(this.Page);
if (IDValue == lnkDynamic.ID)
LinkClick(lnkDynamic, new EventArgs());
}
}
Calling the click event handler here also more closely mimics the standard ASP.NET Page Life Cycle, where Postback event handling occurs after the Load event.
Edit:
If the control ID must be determined before the LinkButtons are created, you can create a naming scheme for the link button IDs, e.g. lnkDynamic_1, lnkDynamic_2 etc.
Request["__EVENTTARGET"] will then contain the auto-generated control ID such as “ctl00$mc$lnkDynamic_1”, which you can use to identify which LinkButton caused the postback.

If You're getting the post back control id correctly but FindControl returns nothing, then it's probably because You're using a master page. Basically, someControl.FindControl(id) searches through controls that are in someControl.NamingContainer naming container. But in Your case, the Button1 control is in the ContentPlaceHolder1, which is a naming container, and not directly in the Page naming container, so You won't find it by invoking Page.FindControl. If You can't predict in which naming container the control You're looking for is going to be (e.g. post back can be caused by two different buttons from two different content placeholders), then You can write an extension that'll search for a control recursively, like so:
public static class Extensions
{
public static Control FindControlRecursively(this Control control, string id)
{
if (control.ID == id)
return control;
Control result = default(Control);
foreach (Control child in control.Controls)
{
result = child.FindControlRecursively(id);
if (result != default(Control)) break;
}
return result;
}
}
Use it with caution though, because this method will return the first control that it finds with the specified id (and You can have multiple controls with the same id - but they should be in different naming containers; naming containers are meant to differentiate between controls with same ids, just as namespaces are meant to differentiate between classes with same names).
Alternatively, You could try to use FindControl(string id, int pathOffset) overload, but I think it's pretty tricky.
Also, check this question out.

First approach (wouldn't recommend but it's more flexible)
One completely different approach - although I don't really feel like I should promote it - is to add a hidden field to the form.
The value of this hidden field might be something like false by default.
In case of clicking one of the dynamic buttons which should cause the dynamic controls to be added again, you can simply change the hidden fields value to true on client side before performing the postback (eventually you want/have to modify the client side onclick handler to make this happen).
Of course it would be possible to store more information in such a field, like the controls id and the argument (but you can get those values as described in the other answers). No naming schema would be required in this case.
This hidden field could be "static". So it would be accessible in code behind all time. Anyhow, you might want to implement something to make sure that nobody is playing around with its values and fakes a callback which looks like it originated from one of these dynamic links.
However, this whole approach just helps you getting the id of the control. Until you create the control again, you won't be able to get the instance through NamingContainer.FindControl (as mentioned in the other answers already ;)). And in case you create it, you don't need to find it anymore.
Second approach (might not be suitable due to its contraints)
If you want to do it the clean way, you need to create your controls OnLoad, no matter if something was clicked or not. Additionally, the dynamic controls ID has to be the same as the one you sent to the client in the first place. You subscribe to its Click or Command event and set its visibility to false. Inside the click event handler, you set the senders visibility to true again. This implies, that you don't care if that link is created but instead just don't want to send it to the client. The example below only works for a single link of course (but you could easily modify it to cover a whole group of links).
public void Page_Load(object sender, EventArgs e)
{
LinkButton dynamicButton = new LinkButton();
dynamicButton.ID = "linkDynamic123";
// this id needs to be the same as it was when you
// first sent the page containing the dynamic link to the client
dynamicButton.Click += DynamicButton_Click;
dynamicButton.Visible = false;
Controls.Add(dynamicButton);
}
public void DynamicButton_Click(object sender, EventArgs e)
{
// as you created the control during Page.Load, this event will be fired.
((LinkButton)sender).Visible = true;
}