Showing posts with label Cookies. Show all posts
Showing posts with label Cookies. Show all posts

Thursday, June 21, 2012

ViewState in asp.net : basic concept of asp.net,use of ViewState,how to use ViewState,need of Cookies in asp.net application...



Another approach to saving data for the user, is the ViewState.

As described elsewhere in this tutorial, the ViewState allows ASP.NET to repopulate form fields on each postback to the server, making sure that a form is not automatically cleared when the user hits the submit button.

All this happens automatically, unless you turn it off, but you can actually use the ViewState for your own purposes as well. Please keep in mind though, that while cookies and sessions can be accessed from all your pages on your website, ViewState values are not carried between pages.

Here is a simple example of using the ViewState to carry values between postbacks:


<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!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>ViewState</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:TextBox runat="server" id="NameField" />
        <asp:Button runat="server" id="SubmitForm" onclick="SubmitForm_Click" text="Submit & set name" />
        <asp:Button runat="server" id="RefreshPage" text="Just submit" />
        <br /><br />
        Name retrieved from ViewState: <asp:Label runat="server" id="NameLabel" />
    </form> 
</body>
</html>

And the CodeBehind:

using System;
using System.Data;
using System.Web;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if(ViewState["NameOfUser"] != null)
            NameLabel.Text = ViewState["NameOfUser"].ToString();
        else
            NameLabel.Text = "Not set yet...";
    }

    protected void SubmitForm_Click(object sender, EventArgs e)
    {
        ViewState["NameOfUser"] = NameField.Text;
        NameLabel.Text = NameField.Text;
    }
}

Try running the project, enter your name in the textbox and press the first button.

The name will be saved in the ViewState and set to the Label as well.

No magic here at all. Now press the second button.

This one does nothing at all actually, it just posts back to the server. As you will notice, the NameLabel still contains the name, but so does the textbox. The first thing is because of us, while the textbox is maintained by ASP.NET it self.

Try deleting the value and pressing the second button again. You will see that the textbox is now cleared, but our name label keeps the name, because the value we saved to the ViewState is still there!

ViewState is pretty good for storing simple values for use in the form, but if you wish to save more complex data, and keep them from page to page, you should look into using cookies or sessions, as described in the previous chapters.

from...

http://asp.net-tutorials.com/state/viewstate/

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Cookies in asp.net : basic concept of Sessions,use of Sessions,how to use Sessions,need of Sessions in asp.net application...



Sessions can be used to store even complex data for the user just like cookies. Actually,

sessions will use cookies to store the data, unless you explicitly tell it not to. Sessions can be used easily in ASP.NET with the Session object.

We will re-use the cookie example, and use sessions instead.

Keep in mind though, that sessions will expire after a certain amount of minutes, as configured in the web.config file. Markup code:

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!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>Sessions</title>
</head>
<body runat="server" id="BodyTag">
    <form id="form1" runat="server">
    <asp:DropDownList runat="server" id="ColorSelector" autopostback="true" onselectedindexchanged="ColorSelector_IndexChanged">
        <asp:ListItem value="White" selected="True">Select color...</asp:ListItem>
        <asp:ListItem value="Red">Red</asp:ListItem>
        <asp:ListItem value="Green">Green</asp:ListItem>
        <asp:ListItem value="Blue">Blue</asp:ListItem>
    </asp:DropDownList>
    </form>
</body>
</html>


And here is the CodeBehind: 

using System;
using System.Data;
using System.Web;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if(Session["BackgroundColor"] != null)
        {
            ColorSelector.SelectedValue = Session["BackgroundColor"].ToString();
            BodyTag.Style["background-color"] = ColorSelector.SelectedValue;
        }
    }

    protected void ColorSelector_IndexChanged(object sender, EventArgs e)
    {
        BodyTag.Style["background-color"] = ColorSelector.SelectedValue;
        Session["BackgroundColor"] = ColorSelector.SelectedValue;
    }
}


As you can see, the example doesn't need a lot of changes to use sessions instead of cookies.

Please notice that session values are tied to an instance of your browser. If you close down the browser, the saved value(s) will usually be "lost".

Also, if the webserver recycles the aspnet_wp.exe process, sessions are lost, since they are saved in memory as well.

This can be avoided by saving session states on a separate StateServer or by saving to a SQL server, but that's beyond the scope of this article.

source..

http://asp.net-tutorials.com/state/sessions/

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Cookies in asp.net : basic concept of Cookies,use of Cookies,how to use Cookies,need of Cookies in asp.net application...



Cookies are small pieces of text,

stored on the client's computer to be used only by

the website setting the cookies.

This allows webapplications to save information for the user, and then re-use it on each page if needed. Here is an example where we save a users choice of background
color: 


<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!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>Cookies</title>
</head>
<body runat="server" id="BodyTag">
    <form id="form1" runat="server">
    <asp:DropDownList runat="server" id="ColorSelector" autopostback="true" onselectedindexchanged="ColorSelector_IndexChanged">
        <asp:ListItem value="White" selected="True">Select color...</asp:ListItem>
        <asp:ListItem value="Red">Red</asp:ListItem>
        <asp:ListItem value="Green">Green</asp:ListItem>
        <asp:ListItem value="Blue">Blue</asp:ListItem>
    </asp:DropDownList>
    </form>
</body>
</html>






The page simply contains a DropDownList control, which automatically posts back each time a new item is selected.

It has 3 different colors, besides the default one, which is simply white. Once a new item is selected, the ColorSelector_IndexChanged method is fired, from our CodeBehind file:

using System;
using System.Data;
using System.Web;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if(Request.Cookies["BackgroundColor"] != null)
        {
            ColorSelector.SelectedValue = Request.Cookies["BackgroundColor"].Value;
            BodyTag.Style["background-color"] = ColorSelector.SelectedValue;
        }
    }

    protected void ColorSelector_IndexChanged(object sender, EventArgs e)
    {
        BodyTag.Style["background-color"] = ColorSelector.SelectedValue;
        HttpCookie cookie = new HttpCookie("BackgroundColor");
        cookie.Value = ColorSelector.SelectedValue;
        cookie.Expires = DateTime.Now.AddHours(1);
        Response.SetCookie(cookie);
    }
}


Okay, two different parts to be explained here.

First, the Page_Load method, which is called on each page request. Here we check for a cookie to tell us which background color should be used.

If we find it, we set the value of our dropdown list to reflect this, as well as the background color of the page, simply by accessing the style attribute of the body tag.

Then we have the ColorSelector_IndexChanged method, which is called each time the user selects a new color.

Here we set the background color of the page, and then we create a cookie, to hold the value for us.

We allow it to expire after one hour, and then we set it by calling the SetCookie method on the Response object.

Try running the example, and set a color. Now close the browser, and start it up again. You will see that the choice of color is saved, and it will remain saved for an hour. However, nothing prevents you from saving the choice for much longer. Simply add a bigger value to the expiry date, or set an absolute value for it.





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