Develop Reference

ASP.NET: add postback to anchor

In my javascript file, I got an ajax to get all list and iterate these data and append <a id='userID' class='btn'>Assign ID<> to my list.
So, how do a add postback to these anchor and redirect it inside my method in the server. Below is my code but didn't work. When I click the achor button, it just redirect/refresh to the same page without doing any changes and didn't show the text.
<a id='uniqueID' class='btn assignID' href='javascript:void(0);' onclick='javascript:__doPostBack('uniqueID','')'>Assign ID</a>
protected void Action_assignID(object sender, EventArgs e)
{
// assign ID action
Response.Write("Pass");
}

You should be changed your button to:
<a id='uniqueID' class='btn assignID' href='javascript:void(0);' onclick="javascript:__doPostBack('uniqueID','Assign ID')">Assign ID</a>
And it's a good idea to implement the IPostBackEventHandler interface in your codebehind as below:
public partial class WebForm : Page, IPostBackEventHandler
{
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
}
}
public void RaisePostBackEvent(string eventArgument)
{
// do somethings at here
}
}
Hope this help!

The __doPostBack method really doesn't do anything special except, well... perform a POST operation back to the same page with two specific form arguments.
The first parameter is the __EVENTTARGET and the second parameter is the __EVENTARGUMENT.
The magic all happens in ASP.Net where it automagically wires up your controls to event handlers, but since you are creating these entirely in JavaScript the server doesn't know that those controls exist.
However, you can manually grab these values and do something with them.
//Client Side JavaScript:
__doPostBack('my-event', '42');
//Code Behind
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
var target = Request.Params["__EVENTTARGET"];
var args = Request.Params["__EVENTARGUMENT"];
Target.Text = target; // 'my-event'
Argument.Text = args; // '42'
}
}

How to use ViewState after Request.Form?

Hi I'm trying to save the values from the request.form after post back. I've tried to use viewstate on the input string but the page_load keeps regenerating the request.form
string TID = null;
Protected void Page_Load(object sender, EventArgs e)
{
if (TID == null)
{
TID= Request.Form ["totalID"];
}
Label1.Text = TID;
}
protected void Button2_Click (object sender, EventArgs e)
{
Label1.Text = TID;
}

Most asp.net controls have a text property, so if yours is a TextBox and you named it textBoxTotalID, then you can just get the value entered using this.textBoxTotalID.Text.
Instead of totalID, use the name of the element not the Id. The name is used for posting information to the server. And also make sure you have specified a name in your view for the element whose value you need on post.
In addition to that, ask yourself this question: Do you need to do that even when the user requests the page or only when the form is submitted? I am sure your answer is only when form is submitted. In that case, do it only when IsPostBack is true.

Try adding a check to the IsPostBack property.
if (IsPostBack)
{
//Set Values here
}
This is set to true when the page is responding to a post back from a form submit or perhaps a control event being fired.

Why can't I get the value from textbox?

I've just started learning ASP.NET and I'm facing a problem with getting textbox values. I want to do a simple calculator with only 4 basic operations but what happens is that after I click the + sign and click Go, I see that I didn't store the first number at all. Second number is fine though. Here is a sample of my code.
public partial class deafult : System.Web.UI.Page
{
public TextBox output = new TextBox();
public double temp,tempAdd, calc;
protected void Page_Load(object sender, EventArgs e)
{
}
protected void btnAdd_Click(object sender, EventArgs e)
{
tempAdd = Convert.ToDouble(output.Text);
output.Text = String.Empty;
}
//User enters another number after clicking Add button then clicks Proc
protected void proc_Click(object sender, EventArgs e)
{
temp = Convert.ToDouble(output.Text);
calc = tempAdd + temp;
output.Text = calc.ToString();
}
}
I debugged and tempAdd is always 0 but I get the number in temp. temp variables and calc is defined public.

You essentially have the problem with all of your variables being re-initialized on load of the page. Unlike winforms, web is stateless.
There are ways of persisting state between refreshes, however. The most obvious choice for your application would be to only go to the server once with the both values and what you want to do with them. ie One button click.
However, for personal edification, it may be worth looking up ViewState. This allows you to store values in an array of sorts and retrieve them even after a refresh.
There are also Session and Application level arrays in ASP.NET that work in similar ways.

Every time you call the page (by events) all your properties is initialized.
Try to do all your logic in one event or store your properties in manager / service / db.

In web (Asp.Net) on every postback properties will get cleared, try to use ViewState or Session variables to hold these values. Refer Asp.Net State Management concepts from MS.
Hope this may help you.

Web controls are State less so you should user session sate to hold the first value then do your stuff...
Ex:-
protected void btnAdd_Click(object sender, EventArgs e)
{
Session["tempAdd"] = output.Text;
output.Text = String.Empty;
}
protected void proc_Click(object sender, EventArgs e)
{
temp = Convert.ToDouble(output.Text);
string oldval=Session["tempAdd"] != null ?Session["tempAdd"].ToString() :"";
if(oldval!="")
tempadd=Convert.ToDouble(oldval);
calc = tempAdd + temp;
output.Text = calc.ToString();
}

Passing session variable from page to page

I'm wondering what is my issue on passing a variable from page to page using asp.net session.
I've stripped the code down to just one text box to see whats going on. I'm just trying to take the value of a text box and display it on a confirmation page. When the button is clicked it transfers me to the second page but there label is blank. Yes my post back url is pointing to the second page.
Here is the button click:
protected void submit_Click(object sender, EventArgs e)
{
string name = txtFirstName.Text.Trim();
Session["name"] = name;
}
Here is the page load of the second page:
protected void Page_Load(object sender, EventArgs e)
{
lblName.Text = (string)(Session["name"]);
}
Unless I've been looking at this to long and missed something. I've already read "How to: Read Values from Session State" from MSDN.

You say that you've set the PostBackUrl to your second page. If you're going to do it that way, you need to use Page.PreviousPage to get access to your textbox. But this is the easiest way:
Firstly, leave the PostBackUrl alone. Setting the PostBackUrl to your second page means that you're telling the SECOND PAGE to handle your button click, not the first page. Hence, your session variable never gets set, and is null when you try to pull it.
This should work for ya.
And yes, you can also do this with a QueryString, but if its something that you don't want the user to see/edit, then a Session variable is better.
protected void submit_Click(object sender, EventArgs e)
{
string name = txtFirstName.Text.Trim();
Session["name"] = name;
Response.Redirect("PageTwo.aspx");
}
Then in the second page (You don't REALLY need the ToString()):
protected void Page_Load(object sender, EventArgs e)
{
if (Session["name"] != null)
{
lblName.Text = Session["name"].ToString();
}
}
EDIT -- Make sure that your button click actually gets fired. Someone can correct me wrong on this, as I do most of my work in VB.NET, not C#. But if you don't specify the OnClick value, your function won't get called.
<asp:Button ID="Button1" runat="server" Text="Click Me!" OnClick="submit_Click" />

The code you have posted looks fine, so your problem is probably with setup.
Check this link ASP.NET Session State Overview and pay particular attention to the sections on Cookieless SessionIDs and Configuring Session State.

I don't think you added the session. This is how I have done mine.
First Page
protected void btnView_Click(object sender, EventArgs e)
{
foreach (ListItem li in lbxCheckDates.Items)
{
if (li.Selected == true)
{
lblMessage.Text = "";
string checkDate = lbxCheckDates.SelectedItem.Text;
Session.Add("CheckDates", checkDate);
Page.ClientScript.RegisterStartupScript(
this.GetType(), "OpenWindow", "window.open('Paystub.aspx','_newtab');", true);
}
}
}
Second Page
protected void Page_Load(object sender, EventArgs e)
{
string checkDate = (string)(Session["CheckDates"]);
//I use checkDate in sql to populate a report viewer
}
So with yours, I think you need..
protected void submit_Click(object sender, EventArgs e)
{
string name = txtFirstName.Text.Trim();
Session.Add("Name", name);
}
I think what you have in the second page should work, but if it doesn't, add ToString() to it like..
lblName.Text = (string)(Session["name"]).ToString();
Let me know if this helps!

Are you doing a redirect after setting the session variable on the first page, if so you it will not work correctly (unless you know the trick). Checkout this article on making it work. Basically, the way to make this work is to the overload redirect method.
Response.Redirect("~/newpage.aspx", false);
The false parameter prevents .net from terminate processing on the existing page (that actually writes out the session state)

For Second Page
protected void Page_Load(object sender, EventArgs e)
{
if (Session["value"] != null)
{
Label1.Text = Session["value"].ToString();
}
else
{
Label1.Text = "Sorry,Please enter the value ";
}
}

You can use Server.Transfer() instead of Response.Redirect()

For first page, use this:
protected void Button1_Click(object sender, EventArgs e)
{
string value = TextBox1.Text;
Session["value"] = value;
Response.Redirect("~/Sessionpage.aspx");
}

Redirect as a fresh request after using Response.Redirect

I am working on an aspx page in VS 2005. I have code like this,
int RepID = 0;
protected void Page_Load(object sender, Eventargs e)
{
if(!Page.Ispostback)
{
get value from database and display it in textbox;
}
else
{
}
}
protected void Save_OnClick(object sender, Eventargs e)
{
Update Database with modified textbox Text ;
Response.Redirect(//To the same page);
}
After the Response.Redirect, i was looking for the page to refresh and get the modified value from database. Instead, it uses the else loop in Page_load and displays the old value because it doesn't go into the if loop as it is the Postback. How can i display from database after the response.redirect is used. I know i am missing a logic but i am not sure what? Thanks alott guys..

Delete
Response.Redirect(//to same page);
Your Save button click should post back to the same page it is on.