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linkbuttons postback before executing click event code?

I am trying to add a basic switch to my site in order to switch between static and responsive layouts.
I have two linkbuttons at the bottom of my page:
<div id="toggleView">
<asp:linkbutton ID="lbtnMobile" runat="server" Visible="false">Switch to Mobile site</asp:linkbutton>
<asp:linkbutton ID="lbtnFull" runat="server" >Switch to Full site</asp:linkbutton>
</div>
They both have a very similar OnClick event.
protected void lbtnFull_Click(object sender, EventArgs e)
{
c.ViewChange = true;
Session["Customer"] = c;
}
protected void lbtnMobile_Click(object sender, EventArgs e)
{
c.ViewChange = false;
Session["Customer"] = c;
}
The events should set a boolean in a class file (User.vb) between true or false and then save the session, on postback the Page_Load event is supposed to read this boolean and use it to adjust the Viewport meta tag:
protected void Page_Load(object sender, System.EventArgs e)
{
//Other Stuff in here, irrelevant to current question
HtmlMeta view = new HtmlMeta();
view.Name = "viewport";
if (c.ViewChange = false)
{
view.Content = "width=device-width, initial-scale=1";
lbtnFull.Visible = true;
lbtnMobile.Visible = false;
}
else
{
view.Content = "width=1040px, initial-scale=1";
lbtnFull.Visible = false;
lbtnMobile.Visible = true;
}
MetaPlaceHolder.Controls.Add(view);
}
However, when I click on the "Switch to Full Site" linkbutton, the page will postback but nothing will have changed. Does the postback get triggered too early somehow?

The page load event will happen BEFORE your click event. Reference this here.
This means your check for the ViewChange will happen before you set it in the OnClick handler.

You should change
if (c.ViewChange = false)
to
if (c.ViewChange == false)
for something to happen. But I think it won't be what you expect. Because page_load is executed before click event. You may move some code from page_load to click event handlers.

When ever you postback the Page_Load always get called. So, the code mentioned inside Page_Load would always get executed.
protected void Page_Load(object sender, System.EventArgs e)
{
... All your mentioned code will be executed.
}
Therefore, you won't find any change in your HTML page currently viewed in a browser because at postback initial content also got executed. You need to wrap your content inside !IsPostBack to make it work properly.
Thus, modify you code in following way.
protected void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostback)
{
... All your mentioned code will be executed during normal load.
}
}
Also, you need to add some extra code in LinkButton click event i.e. what to show and what to hide.

Firstly your implementation in the Page_Load isn't very clear.
Nevertheless this is what I recommend, from what I've understod:
As the page load will get executed before the post-back event like the buton or link click, you need persist the value of the class object
Make a protected property of type of your class (where you store/manage the ViewChange atribute)
The property should internally (in the get & set), hold/persist the value in session/viewstate (similar to what you've written)
The setting and reading should only be by referring the property directly (and not how you've done the click-event)
On clicking of the button and post setting the new value, you will have to redirect to the same page, as only then the Page_Load event will get the new boolean value that you've just changed in the click-event; (Page_Load occurs befoer the any other post-back event)
An alternative to the fresh redirection is that, you could make a function that has the view changing logic (as depicted in your Page_Load code), and this function should be called on your button/link click event (post boolean value change) and also in the Page_Load event, but within the "!IsPostBack" block
Hope this helps you.

Button click event error

Having just added a new button in my web application, I get an error when clicking on it, and I'm wondering if this is related to misplaced code. I will describe what/where I did, briefly. Thanks very much.
In ascx file:
<asp:Button ID="btn_rezerv" runat="server" Text="Reserve film" OnClick="btn_rezerv_Click"/>
In the ascx.cs file:
namespace CinProj.UserControls
{
public partial class FilmsList : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
PopulateControls();
}
private void PopulateControls()
{
string categId = Request.QueryString["CategID"];
string filmId = Request.QueryString["FilmID"];
....
if (categId != null)
{
.....
}
if (filmId != null)
{
......
Button btn_rezerv = (Button)item.FindControl("btn_rezerv");
}
}
protected void btn_rezerv_Click(object sender, EventArgs e)
{
string fid = Request.QueryString["FilmID"];
ShoppingCartAccess.AddItem(fid);
}
}
}
"Server Error in '/' Application.
Invalid postback or callback argument. Event validation is enabled using in configuration or <%# Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation. "

Another problem could be because your PopulateControls method should probably only be called when during the Page Load when it's not a PostBack. I can't tell from above, but to me it looks like it only needs done on Load. Try wrapping that call with this:
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
PopulateControls();
}
}

It's likely the result of making some sort of client change that the server doesn't know about. Many times this is the result of changing values in a dropdown in JavaScript, for example.
To fix, you could:
Do away with using JavaScript for said modification
Use an UpdatePanel and add your control to it. If the client needs to make a change, trigger the UpdatePanel's update in order for the control's viewstate to update.

Calling page event when ASP.NET user control event is invoked

Suppose there is a user control in a page called Paging.ascx that is embedded in PageWithResults.aspx. This control has the necessary properties to keep track of various details about what page you're on (ie: CurrentPage, TotalRecordsInResults, RecordsPerPage, etc..). It also contains events that fire off when you click on a hyperlink ("next page" or "previous page"). Example below. I need to tell PageWithResults.aspx that one of these LinkButton web controls was clicked. I think I need to assign a delegate in the page, so that when this user control event is called (hyperlink is clicked), it also calls some other method/event in the page class. That way I can quickly check what the new value of CurrentPage is (based on what was called in the event below) and get a new result set for the new page (based on the CurrentPage property). But I'm not sure of the best approach. I'm thinking this will require a delegate, but I'm not sure how to wire it up. If you need more details, please ask.
protected void btnNext_Click(object sender, EventArgs e)
{
this.CurrentPage = this.CurrentPage + 1;
if (OnPageChanged != null) OnPageChanged(this.CurrentPage);
}
I'm thinking I have to put my delegate here somewhere. ??
protected void btnNext_Click(object sender, EventArgs e)
{
this.CurrentPage = this.CurrentPage + 1;
if (OnPageChanged != null) OnPageChanged(this.CurrentPage);
//delegate to call object.method or something
}

Using an event would work fine.
You would create the event within your UserControl like so:
public event EventHandler ButtonClicked;
Then invoke the event when required:
protected void Button1_Click(object sender, EventArgs e)
{
if (ButtonClicked != null)
ButtonClicked(this, new EventArgs());
}
In your page you would need to assign an event handler:
protected void Page_Load(object sender, EventArgs e)
{
UserControl1.ButtonClicked += new EventHandler(UserControl1_ButtonClicked);
}
void UserControl1_ButtonClicked(object sender, EventArgs e)
{
}
As well as using the above approach you can also cast the Page reference in the UserControl and call a public method directly:
MyPage page = (MyPage)Page;
page.AMethod();
Hope this helps.

Button.OnClientClick question

I'm gonna post some more code to show exactly what I'm trying to do,
I'm adding the button using programming code and not markup but the OnClick won't work (giving the following error:
System.Web.UI.WebControls.Button.OnClick(System.EventArgs)' is inaccessible due to its protection level.
Button btnopslaan = new Button();
btnopslaan.Text = "Opslaan";
btnopslaan.ID = "btnOpslaan";
btnopslaan.CssClass = ".opslaan";
btnopslaan.Click += new EventHandler(btnopslaanClick);
btnopslaan_arr[btn_count] = btnopslaan;
add_button(btnopslaan);
protected void btnopslaanClick(object sender, EventArgs e)
{
Debug.WriteLine("success");
}
I just can't find out why this isn't working.
Anyone who can help me out?

You need to use OnClick for server side clicks rather than OnClientClick
Either you can use it inline >
<asp:Button id="btnopslaan" runat="server' OnClick="btnopslaanClick" />
Or in Code behind >
btnopslaan.Click+=new EventHandler(btnopslaanClick);

or you make it a postback call to the server. in your
aspx write:
<asp:Button runat="server" ID="buttonOpslaan" Text="opslaan" ></asp:Button>
codebehind write this:
protected void Page_Init(object sender, EventArgs e)
{
buttonOpslaan.Click += new EventHandler(buttonOpslaan_Click);
}
// mind: this method can be private
void buttonOpslaan_Click(object sender, EventArgs e)
{
//do something
}
or handle it with the AutoEventWireUp (recommended) like:
<asp:Button runat="server"
ID="buttonOpslaan"
OnClick="buttonOpslaan_Click"
Text="opslaan" ></asp:Button>
// mind: this method cannot be private, but has to be protected at least.
protected void buttonOpslaan_Click(object sender, EventArgs e)
{
//do something
}
or do it completely from code behind:
// note: buttonOpslaan must have an (autoassigned) ID.
protected void Page_Init(object sender, EventArgs e)
{
Button buttonOpslaan = new Button();
buttonOpslaan.Text = "opslaan!";
buttonOpslaan.Click += new EventHandler(buttonOpslaan_Click);
form1.Controls.Add(buttonOpslaan);
}
protected void buttonOpslaan_Click(object sender, EventArgs e)
{
//do something
}
or handle it clientside with javascript in your ASPX (it will not reach the server)
<script type="text/javascript">
function buttonOpslaan_Click(){
alert("test");
return false;
}
</script>
<asp:Button runat="server"
ID="buttonOpslaan"
OnClientClick="buttonOpslaan_Click()"
Text="opslaan" ></asp:Button>
Update: (by comments)
if you add the control via an eventhandler (like the onchange event of a dropdownlist), the control is 'lost' on next postback, or even as soon as the Page is send to the client (due to the stateless (there is no mechanism to maintain the state of application) behaviour and lifecycle of .Net).
So simply adding a control once is never going to work.
That means you have to rebuild the control every time a postback occurs. My preferred way to do this is store a list/document somewhere that descrbes what controls must be created each time. Possible locations are, from worse to good (IMHO):
Session
Viewstate
Cache
XML/IO
Database
After all, you are posting "data" to the server (that represents a control) and you want to save that for further use.
If the controls to be created aren't that complex you could implement a Factory Pattern like a WebControlFactory that stores only a few properties in a List or Dictionary, which is read every time to recreate the controls again (and again, and again, and again)

btnopslaanClick should be client side, in the .aspx itself have:
<script type="text/javascript">
function btnopslaanClick() {
alert("success");
}
</script>

btnopslaan.Click+=new EventHandler(btnopslaanClick);
protected void btnopslaanClick(object sender, EventArgs e)
{
Debug.WriteLine("succes");
}

using sessions variable

In my master page, I'm loading a variable in the session like this:
public partial class TheMasterPage : System.Web.UI.MasterPage
{
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
ViewUserPreferences SessionUserPreferences = new ViewUserPreferences();
SessionUserPreferences = UserPreferences.GetUserPreferencesFromDB(6);
}
}
}
Then, in the code behind of a file, I have this:
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
var test = Session["SessionUserPreferences"];
}
}
But when I debug, test is null. What's causing the problem?
Also, if I put a break point in the master page, it doesn't trigger when I run the aspx page; is this normal?
Thanks.

First thing you are missing the assignment part for UserPreferences.GetUserPreferencesFromDB(6) to the Session object. (I read the comments for #Greg's answer and you mentioned that even after that it is not working.)
Second, Master Page's Page_Load Event is triggered after the Current Page's Page_Load Event, hence the value of Session["SessionUserPreferences"] is null in Current Page's Page Load event since it is not set yet.
Check this link for further information on Page Events:
http://msdn.microsoft.com/en-us/library/dct97kc3.aspx

You have to do Session["SessionUserPreferences"] = something; somewhere before you attempt to retrieve that. Are you setting it somewhere else that you didn't show?